Proteopedia - User contributions [en]

Receiver domain of sensor histidine kinase CKI1

2012-06-08T15:06:14Z

Tomas Klumpler: /* CKI1RD structure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium-free and magnesium-bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD structure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='Magnesium-bound form of CKI1RD, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Structure and sequence conservation among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains (CKI1RD numbering)]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3dgf]] - response regulatory signalling protein from ''Thermotoga maritina'' 

== References ==
<references />

[[Category:Topic Page]]
[[Category:Phosphotransferase]]

Receiver domain of sensor histidine kinase CKI1

2012-06-08T15:04:51Z

Tomas Klumpler: /* CKI1RD structure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium-free and magnesium-bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD structure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='Magnesium-bound form of CKI1RD, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Structure and sequence conservation among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3dgf]] - response regulatory signalling protein from ''Thermotoga maritina'' 

== References ==
<references />

[[Category:Topic Page]]
[[Category:Phosphotransferase]]

Receiver domain of sensor histidine kinase CKI1

2012-06-08T15:02:13Z

Tomas Klumpler: /* CKI1RD structure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium-free and magnesium-bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD structure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='Magnesium-bound form of CKI1RD, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3dgf]] - response regulatory signalling protein from ''Thermotoga maritina'' 

== References ==
<references />

[[Category:Topic Page]]
[[Category:Phosphotransferase]]

Receiver domain of sensor histidine kinase CKI1

2012-06-08T14:57:26Z

Tomas Klumpler:

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium-free and magnesium-bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD structure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3dgf]] - response regulatory signalling protein from ''Thermotoga maritina'' 

== References ==
<references />

[[Category:Topic Page]]
[[Category:Phosphotransferase]]

Receiver domain of sensor histidine kinase CKI1

2012-06-08T14:50:18Z

Tomas Klumpler:

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD structure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3dgf]] - response regulatory signalling protein from ''Thermotoga maritina'' 

== References ==
<references />

[[Category:Topic Page]]
[[Category:Phosphotransferase]]

Receiver domain of sensor histidine kinase CKI1

2012-06-08T14:48:02Z

Tomas Klumpler:

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD structure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3dgf]] - response regulatory signalling protein from ''Thermotoga maritina'' 

== References ==
<references />

[[Category:Topic Page]]

Category:Receiver

2012-06-08T14:41:59Z

Tomas Klumpler:

List of pages with the keyword Receiver
* [[Receiver domain of sensor histidine kinase CKI1]]

Category:Two component receiver domain

2012-06-08T14:41:37Z

Tomas Klumpler:

List of pages with the keyword Two component receiver domain
* [[Receiver domain of sensor histidine kinase CKI1]]

Category:Receiver domain

2012-06-08T14:41:04Z

Tomas Klumpler:

List of pages with the keyword Receiver domain
* [[Receiver domain of sensor histidine kinase CKI1]]

Category:Signal regulator receiver domain

2012-06-08T14:40:45Z

Tomas Klumpler:

List of pages with the keyword Signal regulator receiver domain
* [[Receiver domain of sensor histidine kinase CKI1]]

Category:Signal receiver domain

2012-06-08T14:39:17Z

Tomas Klumpler:

List of pages with the keyword Signal receiver domain
* [[Receiver domain of sensor histidine kinase CKI1]]

Proteopedia:Table of Contents

2012-06-08T14:37:54Z

Tomas Klumpler:

This guide to the contents of Proteopedia is maintained manually (not automatically generated) and so is inevitably incomplete. Please be sure to use the [[Help:Searching|search slots at the left]] if you don't find what you are looking for below. Updated: {{REVISIONDAY2}}-{{REVISIONMONTH}}-{{REVISIONYEAR}} (DD-MM-YYYY)

'''When you create a new page in Proteopedia, please add it to corresponding topic subpages.'''

==Topics Pages Organized by Category==
{{#tree:id=OrganizedByTopic|openlevels=0|

* Diseases & Related Topics
** [[Alzheimer's Disease]]
** [[Antibody]]
** [[Bacterial Infections]]
** [[Cancer]]
** [[Diabetes & Hypoglycemia]]
** [[Hemophilia]]
** [[HIV]]
** [[Hypertension & Congestive Heart Failure]]
** [[Immune Response]]
** [[Inflammation & Rheumatoid Arthritis]]
** [[Influenza]]
** [[Metabolic Disorders]]
** [[Neurodevelopmental Disorders]]
** [[Oncogenes]]
** [[Pharmaceutical Drugs]]
** [[Pharmaceutical Drug Targets]]
** [[Toxins]]
** [[Viral Infections]]

* Enzymes
** [[Hydrolases]]
** [[Isomerases]]
** [[Ligases]]
** [[Lyases]]
** [[Oxidoreductases]]
** [[Transferases]]

* Gene Expression & Replication
** [[DNA Replication]]
** [[Nucleic Acids]]
** [[Regulation of Gene Expression]]
** [[RNAi]]
** [[Transcription & RNA Processing]]
** [[Translation]]

* Metabolism
** [[Amino Acid Synthesis & Metabolism]]
** [[Carbohydrate Metabolism]]
** [[Photosynthesis]]
** [[Regulation of Gene Expression]]

* Signaling & Transport
** [[Hormone]]
** [[Membrane Channels & Pumps]]

* Miscellaneous
** [[Colored & Bioluminescent Proteins]]

* Structural Biology
** [[Carbohydrates]] [[Image:New yellow1.gif]]
** [[Intro. to Protein Structure]] [[Image:New yellow1.gif]]
** [[About_Macromolecular_Structure|Macromolecular Structure]]
** [[Structural Biology]]
}}
__NOTOC__
__NOEDITSECTION__

Proteopedia:Table of Contents

2012-06-08T14:36:08Z

Tomas Klumpler:

This guide to the contents of Proteopedia is maintained manually (not automatically generated) and so is inevitably incomplete. Please be sure to use the [[Help:Searching|search slots at the left]] if you don't find what you are looking for below. Updated: {{REVISIONDAY2}}-{{REVISIONMONTH}}-{{REVISIONYEAR}} (DD-MM-YYYY)

'''When you create a new page in Proteopedia, please add it to corresponding topic subpages.'''

==Topics Pages Organized by Category==
{{#tree:id=OrganizedByTopic|openlevels=0|

* Diseases & Related Topics
** [[Alzheimer's Disease]]
** [[Antibody]]
** [[Bacterial Infections]]
** [[Cancer]]
** [[Diabetes & Hypoglycemia]]
** [[Hemophilia]]
** [[HIV]]
** [[Hypertension & Congestive Heart Failure]]
** [[Immune Response]]
** [[Inflammation & Rheumatoid Arthritis]]
** [[Influenza]]
** [[Metabolic Disorders]]
** [[Neurodevelopmental Disorders]]
** [[Oncogenes]]
** [[Pharmaceutical Drugs]]
** [[Pharmaceutical Drug Targets]]
** [[Toxins]]
** [[Viral Infections]]

* Enzymes
** [[Hydrolases]]
** [[Isomerases]]
** [[Ligases]]
** [[Lyases]]
** [[Oxidoreductases]]
** [[Transferases]]

* Gene Expression & Replication
** [[DNA Replication]]
** [[Nucleic Acids]]
** [[Regulation of Gene Expression]]
** [[RNAi]]
** [[Transcription & RNA Processing]]
** [[Translation]]

* Metabolism
** [[Amino Acid Synthesis & Metabolism]]
** [[Carbohydrate Metabolism]]
** [[Photosynthesis]]
** [[Regulation of Gene Expression]]

* Signaling & Transport
** [[Hormone]]
** [[Membrane Channels & Pumps]]
** [[Plant hormone signaling proteins]]

* Miscellaneous
** [[Colored & Bioluminescent Proteins]]

* Structural Biology
** [[Carbohydrates]] [[Image:New yellow1.gif]]
** [[Intro. to Protein Structure]] [[Image:New yellow1.gif]]
** [[About_Macromolecular_Structure|Macromolecular Structure]]
** [[Structural Biology]]
}}
__NOTOC__
__NOEDITSECTION__

Hormone

2012-06-08T14:32:48Z

Tomas Klumpler: /* Guide to Proteopedia Pages Concerning Hormones and their Receptors */

[[Image:1xwd polyview3d.png|right|390px]]
In the field of modern endocrinology, a [[Hormone|hormone]] is any substance, generated either externally or internally, that operates via a receptor at the cellular level, which conveys to to the cell a message to stop, start, or modulate a cellular process.
{{TOC limit|limit=2}}
==Guide to Proteopedia Pages Concerning Hormones and their Receptors==
{{Structure
|PDB=
|SIZE=380|SCENE=Human_Follicle-Stimulating_Hormone_Complexed_with_its_Receptor/1fl7to1xwdmorph/4|CAPTION= FSH binding to the leucine-rich domain of Follicle Stimulating Hormone Receptor ([[1fl7]] morphing to [[1xwd]], [[resolution]] 2.92Å)
|SITE=
|LIGAND=
|ACTIVITY=
|GENE=
|DOMAIN=
|RELATEDENTRY=
|RESOURCES=
|COORDINATES=
}}
{{#tree:id=HormoneTopic|openlevels=0|
Articles in Proteopedia concerning [[Hormone]] include:
* [[Human Follicle-Stimulating Hormone Complexed with its Receptor]]
* [[Leucine-rich repeat|Leucine-rich repeat proteins]]
* [[Vascular Endothelial Growth Factor]]
* [[Vascular Endothelial Growth Factor Receptor]]
* [[Receiver domain of sensor histidine kinase CKI1]]

}}
 

To view automatically seeded indices concerning [[Hormone]], see:
*[[:Category:Hormone|Hormone]]
*[[:Category:Hormone receptor|Hormone Receptor]]
*[[:Category:Steroid receptor|Steroid receptor]]
*[[:Category:Steroid hormone receptor|Steroid hormone receptor]]
 

==Additional 3D Structures of Hormones and Hormone Receptors and Related Molecules==
===Angiotensinogen===
[[2wxw]], [[2wxx]], [[2wxy]], [[2wxz]], [[2wy0]], [[2wy1]], [[2x0b]] - Angiotensinogen – human, rat, mouse 

===Chorionic Gonadotropin===
[[1hrp]] - Chorionic Gonadotropin – human 
[[1hcn]] - Chorionic Gonadotropin – human 
[[1hd4]] - Alpha-subunit of Chorionic Gonadotropin – human 

===Follicle-Stimulating Hormone===
[[1fl7]] - Follicle-Stimulating Hormone – human 
[[1xwd]] - Human Follicle Stimulating Hormone complexed with its Receptor – human 

===Glucocorticoid===
[[3mne]], [[3mno]], [[3mnp]] - Glucocorticoid Receptor Ligand-binding Domain – human 

===Growth Hormone===
[[3hhr]] - Growth Hormone complexed with the extracellular portion of its receptor - human 
[[1hwh]] - Growth Hormone Mutant G120R complexed with the extracellular portion of its receptor - human 
[[1bp3]] - Growth Hormone complexed with the prolactin receptor - human 
[[3mjg]], [[3mjk]] - Platelet-derived Growth Factor/Propeptide Complex and a Platelet-Derived Growth Factor/Receptor Complex – human 
Vascular Endothelial Growth Factor – human and others, see [[VEGF#Additional_3D_Structures_of_VEGF|Vascular Endothelial Growth Factor Structures]] 
Vascular Endothelial Growth Factor Receptor – human, see [[VEGFR#Additional_3D_Structures_of_VEGFR|Vascular Endothelial Growth Factor Receptor Structures]] 
[[2xdg]] - Extracellular Domain of Human Growth Hormone Releasing Hormone Receptor – human 

===Insulin===
[[3ir0]] , [[1mso]] , [[1trz]] , [[2qiu]] , [[2r34]], [[2r35]] , [[2r36]], [[3ilg]], [[2kjj]] , [[2kju]] - Insulin – human 
[[3nw5]], [[3nw6]], [[3nw7]] - insulin-like growth factor 1 receptor – human 
[[3loh]], [[2dtg]] - insulin receptor ectodomain – human 

===Progesterone===
[[3hq5]],[[3g8n]], [[3g8o]], [[3hq5]] - Progesterone – human 

===Thyroid-Stimulating hormone===
[[3g04]] - TSH receptor in complex with a thyroid-stimulating autoantibody – human 

===Thyroid hormone===
[[2nll]] - DNA-Binding domain in complex with an inverted repeat class of thyroid response element– rat 
[[1xzx]]

===Thyroxine===
[[2xn3]], [[2xn5]], [[2xn6]], [[2xn7]] - Thyroxine-binding Globulin – human 

===Farnesoid X Receptor ===
[[3olf]], [[3omk]], [[3omm]], [[3oof]], [[3ook]], [[3okh]], [[3oki]] - Farnesoid X Receptor – human 

===PACAP/glucagon family of peptide hormones===
[[3n94]] - PAC1R, receptor of pituitary adenylate cyclase activating polypeptide, is a case of a crystal structure disagreeing with the NMR structure [[2jod]] and vice versa 
[[2jod]] - Pituitary adenylate cyclase-activating polypeptide (residues 6'-38') complexed to the extracellular domain of the human splice variant hPAC1-RS determined by NMR - human 

ADD [[3dzu]]

==See Also==
* [[Cancer]]
* [[Membrane proteins]]
* [[G protein-coupled receptor|G protein-coupled receptors]]

==External Resources==
* [http://www.ssfa-gphr.de/index.php Sequence-Structure-Function-Analysis of Glycoprotein Hormone Receptors]
* [http://www.ssfa-7tmr.de/ssfe/ The GPCR-SSFE Database: A Homology Model Resource for G-Protein Coupled Receptors]
* The [http://www.rcsb.org/pdb/101/motm.do?momID=52 feature on Growth Hormone] by Shuchismita Dutta and David S. Goodsell for the April 2004 RCSB PDB [http://pdb.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/index.html Molecule of the Month].
* [http://proteomics.ucsd.edu/Software/NeuroPedia.html NeuroPedia, a neuropeptide database and spectral library]

[[Category:Topic Page]]
[[Category:Hormone]]
[[Category:Hormones]]
[[Category:Endocrine]]
[[Category:Endocrinology]]
[[Category:Signaling]]
[[Category:Cystine-knot growth factor|Cystine-knot growth factor]]
[[Category:Cyclic cystine knot|Cyclic cystine knot]]
[[Category:Cystine knot superfamily|Cystine knot superfamily]]
[[Category:Cystine knot motif|Cystine knot motif]]

File:CKI1RDmorph.pdb

2012-06-08T14:08:02Z

Tomas Klumpler:

Receiver domain of sensor histidine kinase CKI1

2012-06-08T13:15:07Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD structure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3dgf]] - response regulatory signalling protein from ''Thermotoga maritina'' 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T13:13:38Z

Tomas Klumpler: /* 3D Structures of CKI1RD and most similar receiver domains */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3dgf]] - response regulatory signalling protein from ''Thermotoga maritina'' 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T13:07:03Z

Tomas Klumpler: /* 3D Structures of CKI1RD and most similar receiver domains */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and most similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis'' 
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica'' 
[[3c97]] - response regulator receiver domain of a histidine kinase from ''Aspergillus oryzae'' 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T13:06:41Z

Tomas Klumpler: /* 3D Structures of CKI1RD */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD and most similar receiver domains ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

[[3dcf]] - ETR1RD, receiver domain of plant hormone ethylene receptor from ''Arabidopsis''
[[2chy]] - CheY, chemotaxis response regulatory protein from ''Salmonella enterica''
[[3c97]] - response regulator receiver domain of a histidine kinase from ''Aspergillus oryzae''

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T12:26:03Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T12:25:07Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD magnesium-bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Ribbon diagram of magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T12:21:20Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|350px|right|thumb| (a) Ribbon diagram of magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T12:20:29Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. 
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.
[[Image:CKI1RD_active_site.png|250px|right|thumb| (a) Ribbon diagram of magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T12:19:38Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. [[Image:CKI1RD_active_site.png|250px|right|thumb| (a) Ribbon diagram of magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T12:18:57Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. 
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. [[Image:CKI1RD_active_site.png|250px|right|thumb| (a) Ribbon diagram of magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T12:16:54Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. [[Image:CKI1RD_active_site.png|250px|right|thumb| (a) Ribbon diagram of magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T12:15:25Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992. [[Image:CKI1RD_active_site.png|250px|left|thumb| (a) Ribbon diagram of magnesium-free and (b)magnesium-bound forms of the CKI1RD active site. Magnesium ion (magenta) is approximately octahedrally coordinated. (c) ''2Fo-Fc'' omit map of CKI1RD magnesium bound contoured at 1σ. Conservation of the structure and sequence among known receiver domains. The magnesium ion and all atoms in radius of 5Å were omitted from phasing.]]
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

File:CKI1RD active site.png

2012-06-08T12:07:56Z

Tomas Klumpler:

File:3mmn 3mm4.pdb

2012-06-08T11:44:41Z

Tomas Klumpler:

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:38:32Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene> 
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:37:21Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
<scene name='Receiver_domain/Initial_1/2'>-restore original scene-</scene>
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:34:45Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
(<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium ion</scene> is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:33:29Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
(<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
The octahedral coordination geometry of magnesium ion in this crystal is not complete. <scene name='Receiver_domain/Initial_1/9'> Magnesium</scene>Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:29:33Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
(<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:28:09Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. (<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:27:00Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/7'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. (<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:16:10Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. (<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:13:59Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/5'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. (<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:06:48Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/5'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. (<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. <qt>file=Cki1rd.morph.mov|width=320|height=298|autoplay=true|controller=true|loop=true</qt>
Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:01:23Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/5'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. (<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:00:50Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/5'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>), formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. (<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T11:00:10Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with (<scene name='Receiver_domain/Initial_1/5'> phosphoacceptor D1050</scene>) is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>), formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. (<scene name='Receiver_domain/Initial_1/2'> restore original scene</scene>)
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T10:58:34Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with (<scene name='Receiver_domain/Initial_1/5'> phosphoacceptor D1050 </scene>)is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens </scene>), formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T10:56:58Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with (<scene name='Receiver_domain/Initial_1/5'> phosphoacceptor D1050 </scene>)
is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens </scene>), formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T10:52:23Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with phosphoacceptor D1050 is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens </scene>), formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T10:52:06Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'> The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with phosphoacceptor D1050 is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens </scene>), formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T10:50:37Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>

The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with phosphoacceptor D1050 is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens </scene>), formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T10:47:00Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>

The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (a/ß)5 manner with central ß-sheet formed from parallel beta-strands (ß2-ß1-ß3-ß4-ß5) surrounded on both sides by two (a1 and a5) and three (a2, a3, a4) a-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with phosphoacceptor D1050 is located at the C-termini of the central ß3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens </scene>), formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T10:46:18Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>

The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (a/ß)5 manner with central ß-sheet formed from parallel beta-strands (ß2-ß1-ß3-ß4-ß5) surrounded on both sides by two (a1 and a5) and three (a2, a3, a4) a-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with phosphoacceptor D1050 is located at the C-termini of the central ß3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved (<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens </scene>),

formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />

Receiver domain of sensor histidine kinase CKI1

2012-06-08T10:45:34Z

Tomas Klumpler: /* CKI1RD tructure and effects of magnesium binding in the active site */

[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]]

{{STRUCTURE_3mmn| right| PDB=3mmn |
[[3mmn]] }}

'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium free and magnesium bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy.

== Biological Function ==
[[Image:Cki1signalizace.png|250px|left|thumb| CKI1 acts as constitutively active histidine-kinaze in MSP signaling in ''Arabidopsis''.]]

'''CKI1 as member of Multistep phosphorelay signaling in ''Arabidopsis''''' 
The sensor histidine kinase CKI1 was identified as an activator of a cytokinin-like response when overexpressed in hypocotyl explants <ref>PMID:8875940</ref> and it was shown to be essential for the female gametophyte development<ref>PMID:12426401</ref><ref>PMID:12774227</ref>. Cytokinin response in ''Arabidopsis'' involves shoot and root growth regulation, leaf senesce, circadian rhythms and more<ref>PMID:22639635</ref>. No cytokinin binding to CKI1 has been detected, and in contrast to the genuine cytokinin receptors of ''Arabidopsis'', CKI1 was found to be constitutively active in bacteria and yeast or ''Arabidopsis'' protoplasts<ref>PMID:11577198</ref><ref>PMID:11574878</ref>.
Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs.
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>.

==CKI1RD tructure and effects of magnesium binding in the active site==
<StructureSection load='3mmn' size='400' side='right' caption='CKI1RD bound in magnesium bound form, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'>

The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (a/ß)5 manner with central ß-sheet formed from parallel beta-strands (ß2-ß1-ß3-ß4-ß5) surrounded on both sides by two (a1 and a5) and three (a2, a3, a4) a-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with phosphoacceptor D1050 is located at the C-termini of the central ß3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved '''triad of carboxyl oxygens'''
(<scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens </scene>),

formed by D1050 together with D992 and D993 and carbonyl oxygen of Q1052 give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains.
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Conservation of the structure and sequence among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains.]]
The octahedral coordination geometry of magnesium ion in this crystal is not complete. Magnesium ion is four-coordinated with carboxyl oxygens of D993 and D1050, carbonyl oxygen of Q1052 and with one water molecule that forms a hydrogen bridge to the carboxyl oxygen of D992.
Magnesium binding mediates slight structural changes of the active site. Upon magnesium binding, the side chain of the D1050 rotates by 90° toward the divalent cation. The connection via salt bridge between D1050 and K1105 induces the rotation of K1105, whereas the salt bridge remains established.
More, the NMR analysis shows magnesium binding to stabilize conformational flexibility of the loop L3 in the solution<ref>PMID:21569135</ref>.</StructureSection>

== 3D Structures of CKI1RD ==

[[3mm4]] - CKI1RD in metal free form 
[[3mmn]] - CKI1RD in magnesium bound form 

== References ==
<references />