Sandbox Reserved 709: Difference between revisions

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===Cytoplasm to nucleus===

[[Image:Nuclear_import_protein.png | ~~600px~~ | right |thumb]]

[[Image:Nuclear_import_protein.png | 550px | right |thumb|Nuclear import of proteins through importins α and β]]

To initiate the transport to the nucleus, most of the NLS-containing proteins (or cargos) have to be recognized by a '''Nuclear Import Receptor'''. These are soluble cytosolic proteins such as '''importin α''' and '''[[Importin β|importin β]]'''.

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===Cargo release and protein recycling===

Once the import complex enters the nucleus, it must be dissociated to release the cargo protein. Then, importin α must be recycled to the cytoplasm.

Once the import complex enters the nucleus, it must be '''dissociated''' to release the cargo protein. Then, importin α must be '''recycled''' to the cytoplasm.

* '''Step 4 :''' Cargo release is driven by '''[[Ran|Ran]]''', a '''[[G-protein|G-protein]]''' that is found in Ran-GTP form in the nucleus due to a higher rate of RanGEF than RanGAP in chromatin. It binds to importin β, causing an important change in shape and reducing importin β affinity for importin α IBB.

* '''Step 4 :''' Cargo release is driven by '''[[Ran|Ran]]''', a '''[[G-protein|G-protein]]''' that is found in '''Ran-GTP''' form in the nucleus due to a higher rate of RanGEF than RanGAP in chromatin. It binds to importin β, causing an important change in shape and reducing importin β affinity for '''importin α IBB'''.

* '''Step 5 :''' Importin β can pass through the NPC thanks to Ran-GTP. A '''Ran-BP''' (''Ran-Binding Protein'') is a major component of the NPC’s cytoplasmic filaments. Thus, Ran-GTP is not released in the cytoplasm, but is still bound with importin β to the NPC. Ran-BP is also able to bind to a RanGAP. Finally, RanGAP locally promotes hydrolysis of Ran-GTP into Ran-GDP, leading to its own release, and importin β release by the same.

* '''Step 5 :''' Importin β can pass through the NPC thanks to Ran-GTP. A '''Ran-BP''' (''Ran-Binding Protein'') is a major component of the NPC’s cytoplasmic filaments. Thus, Ran-GTP is not released in the cytoplasm, but is still bound with importin β to the NPC. Ran-BP is also able to bind to a '''RanGAP'''. Finally, RanGAP locally promotes hydrolysis of '''Ran-GTP''' into '''Ran-GDP''', leading to its own release, and importin β release by the same.

* '''Step 6 :''' '''[[Nup50|Nup50]]''' (also called '''[[Nup50|Npap60]]'''), a nucleoplasmin, weakens the link between importin α and the NLS of the cargo. Thus the cargo protein is now free in the nucleoplasm.

* '''Step 6 :''' '''[[Nup50|Nup50]]''' (also called '''[[Nup50|Npap60]]'''), a nucleoplasmin, weakens the link between '''importin α''' and the '''NLS''' of the cargo. Thus the cargo protein is now free in the nucleoplasm.

* '''Step 7 :''' Importin α can’t leave the nucleus only with the help of Ran-GTP. It needs also interaction with '''[[CAS|CAS]]''' (''Cellular Apoptosis Susceptibility'' protein), an '''exportin''' which is similar in shape to importin β. Binding between CAS and importin α is favoured by interactions with Nup50.

* '''Step 8 :'''The newly formed '''importin α:CAS:Ran-GTP''' complex is able to interact with nucleoplasmins of NPC, and once in the cytoplasm, Ran-GTP is hydrolysed into Ran-GDP (''see '''Step 5''' for details''). The complex splits, and importin α is now ready for a new import cycle.<ref>PMID:16222336</ref>

* '''Step 8 :'''The newly formed '''importin α:CAS:Ran-GTP''' complex is able to interact with nucleoplasmins of NPC, and once in the cytoplasm, Ran-GTP is hydrolysed into Ran-GDP (''see '''Step 5''' for details''). The complex splits, and importin α is now ready for a '''new import cycle'''.<ref name ="NUP50">PMID:16222336</ref>

==Importin α structure==

''(<scene name='Sandbox_Reserved_709/Importin_default/1'>Back to the default scene</scene>)''

'''Importin α''' is a soluble adaptor protein also known as '''karyopherin α'''. Its function is to bind a protein containing a cNLS (''classical Nuclear Localization Signal'') and then to bind an importin β in order to help the import of this protein in the nucleus.

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* '''A CAS-binding site.'''

~~<scene name='Sandbox_Reserved_709/Importin_default/1'>Back to the default scene</scene>~~

==Importin α : Nup50 complex==

''(<scene name='Sandbox_Reserved_709/Impnup_default/2'>Back to Default scene </scene>)''

'''Nup50''' (''Nucleoporin 50 kDa'', about 450 aminoacids) is a part of the '''NPCs''', in the '''nucleoplasmic side'''. It is able to bind to <scene name='Sandbox_Reserved_709/Importin/2'>importin importin α</scene> thanks to <scene name='Sandbox_Reserved_709/Nup50/3'>two binding segments</scene> on its N-terminus (''only 46 first aminoacids represented on the structure'').

~~Nup50~~ (''~~Nucleoporin 50 kDa~~''~~, about 450 aminoacids~~) ~~is a part~~ of ~~the NPCs, in the nucleoplasmic side~~. It is ~~able to bind to~~ <scene name='Sandbox_Reserved_709/~~Importin~~/2'> ~~importin α~~ </scene>~~thanks to <scene name='Sandbox_Reserved_709/~~Nup50~~/3'>two~~ binding ~~segments</scene> on its N~~-~~terminus (~~''~~only 40 first aminoacids represented on the structure~~'').

* The first one (''1-15'') binds to the '''minor NLS binding site''' of importin α. This binding is allowed by the '''two basic aminoacids''' <scene name='Sandbox_Reserved_709/Nup_bindingnls/1'>Lys3 and Arg4</scene> of Nup50. In fact, the positive charge will establish bonds with acidic aminoacids of the NLS binding site, just as an NLS-containing cargo would do. In presence of Nup50, the complex importin α:NLS dissociation rate is higher than the one of spontaneous dissociation : there is a '''competition''' between Nup50 and NLS, whose affinities for the NLS minor binding site are in the same order of magnitude. <ref name ="NUP50"/>

* The first one (''1-15'') binds to the '''minor NLS binding site''' of importin α. This binding is allowed by the '''two basic aminoacids'''<scene name='Sandbox_Reserved_709/Nup_bindingnls/1'>Lys3 and Arg4</scene> of Nup50. In fact, the positive charge will establish bonds with acidic aminoacids of the NLS binding site, just as an NLS-containing cargo would do. In presence of Nup50, the complex importin α:NLS dissociation rate is higher than the one of spontaneous dissociation : there is a '''competition''' between Nup50 and NLS, whose affinities for the NLS minor binding site are in the same order of magnitude.

* The second one (''24-46'') binds to the '''C-terminus''' of importin α. Nup50 basic residues 41-46 ('''KKAKRR''') are directed by the formation of '''two turns of an α helix''' (''31-36'' SEEVMK) towards an <scene name='Sandbox_Reserved_709/Nup50_bindingcas/1'>acidic surface</scene> on ARM10. Those electrostatic interactions are essential for the binding of Nup50. Indeed, replacing residues 41-46 by Ala makes the binding undetectable. Furthermore, this binding overlaps the '''CAS''' and the '''Ran binding sites''', explaining why interaction between Nup50 and importin is crucial for building the '''export complex'''.<ref name ="NUP50"/>

* The second one (''24-46'') binds to the '''C-terminus''' of importin α. Nup50 basic residues 41-46 ('''KKAKRR''') are directed by the formation of two turns of an α helix (''31-36'' SEEVMK) towards an <scene name='Sandbox_Reserved_709/Nup50_bindingcas/1'>acidic surface</scene> on ARM10. Those electrostatic interactions are essential for the binding of Nup50. Indeed, replacing residues 41-46 by Ala makes the binding undetectable. Furthermore, this binding overlaps the CAS and the Ran binding sites, explaining why interaction between Nup50 and importin is crucial for building the export complex.

The chain between the two binding segments is rich in acidic residues, and seems to work as a flexible linker between those two sites.

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[[Category: Mus musculus]]

~~[[Category: Matsuura, Y.]]~~

~~[[Category: Stewart, M.]]~~

[[Category: Importin-alpha]]

[[Category: Nuclear protein]]

~~[[Category: Nuclear transport-complex]]~~

~~[[Category: Nuclear transport-complex nup50]]~~

[[Category: Nucleoporin nup50]]

[[Category: Protein transport]]

[[Category: Protein transport-membrane protein complex]]

[[Category: Protein transport/membrane protein]]

[[Category: Importin aplpha/karyopherin alpha]]

[[Category: Protein binding]]

[[Category: Nucleoplasmin]]

Sandbox Reserved 709: Difference between revisions

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@@ Line 24: / Line 24: @@
 ===Cytoplasm to nucleus===
-[[Image:Nuclear_import_protein.png | 600px | right |thumb]]
+[[Image:Nuclear_import_protein.png | 550px | right |thumb|Nuclear import of proteins through importins α and β]]
 To initiate the transport to the nucleus, most of the NLS-containing proteins (or cargos) have to be recognized by a '''Nuclear Import Receptor'''. These are soluble cytosolic proteins such as '''importin α''' and '''[[Importin β|importin β]]'''.
@@ Line 34: / Line 34: @@
 ===Cargo release and protein recycling===
-Once the import complex enters the nucleus, it must be dissociated to release the cargo protein. Then, importin α must be recycled to the cytoplasm.
+Once the import complex enters the nucleus, it must be '''dissociated''' to release the cargo protein. Then, importin α must be '''recycled''' to the cytoplasm.
-* '''Step 4 :''' Cargo release is driven by '''[[Ran|Ran]]''', a '''[[G-protein|G-protein]]''' that is found in Ran-GTP form in the nucleus due to a higher rate of RanGEF than RanGAP in chromatin. It binds to importin β, causing an important change in shape and reducing importin β affinity for importin α IBB.
+* '''Step 4 :''' Cargo release is driven by '''[[Ran|Ran]]''', a '''[[G-protein|G-protein]]''' that is found in '''Ran-GTP''' form in the nucleus due to a higher rate of RanGEF than RanGAP in chromatin. It binds to importin β, causing an important change in shape and reducing importin β affinity for '''importin α IBB'''.
-* '''Step 5 :''' Importin β can pass through the NPC thanks to Ran-GTP. A '''Ran-BP''' (''Ran-Binding Protein'') is a major component of the NPC’s cytoplasmic filaments. Thus, Ran-GTP is not released in the cytoplasm, but is still bound with importin β to the NPC. Ran-BP is also able to bind to a RanGAP. Finally, RanGAP locally promotes hydrolysis of Ran-GTP into Ran-GDP, leading to its own release, and importin β release by the same.
+* '''Step 5 :''' Importin β can pass through the NPC thanks to Ran-GTP. A '''Ran-BP''' (''Ran-Binding Protein'') is a major component of the NPC’s cytoplasmic filaments. Thus, Ran-GTP is not released in the cytoplasm, but is still bound with importin β to the NPC. Ran-BP is also able to bind to a '''RanGAP'''. Finally, RanGAP locally promotes hydrolysis of '''Ran-GTP''' into '''Ran-GDP''', leading to its own release, and importin β release by the same.
-* '''Step 6 :''' '''[[Nup50|Nup50]]''' (also called '''[[Nup50|Npap60]]'''), a nucleoplasmin, weakens the link between importin α and the NLS of the cargo. Thus the cargo protein is now free in the nucleoplasm.
+* '''Step 6 :''' '''[[Nup50|Nup50]]''' (also called '''[[Nup50|Npap60]]'''), a nucleoplasmin, weakens the link between '''importin α''' and the '''NLS''' of the cargo. Thus the cargo protein is now free in the nucleoplasm.
 * '''Step 7 :''' Importin α can’t leave the nucleus only with the help of Ran-GTP. It needs also interaction with '''[[CAS|CAS]]''' (''Cellular Apoptosis Susceptibility'' protein), an '''exportin''' which is similar in shape to importin β. Binding between CAS and importin α is favoured by interactions with Nup50.
-* '''Step 8 :'''The newly formed '''importin α:CAS:Ran-GTP''' complex is able to interact with nucleoplasmins of NPC, and once in the cytoplasm, Ran-GTP is hydrolysed into Ran-GDP (''see '''Step 5''' for details''). The complex splits, and importin α is now ready for a new import cycle.<ref>PMID:16222336</ref>
+* '''Step 8 :'''The newly formed '''importin α:CAS:Ran-GTP''' complex is able to interact with nucleoplasmins of NPC, and once in the cytoplasm, Ran-GTP is hydrolysed into Ran-GDP (''see '''Step 5''' for details''). The complex splits, and importin α is now ready for a '''new import cycle'''.<ref name ="NUP50">PMID:16222336</ref>
 ==Importin α structure==
+''(<scene name='Sandbox_Reserved_709/Importin_default/1'>Back to the default scene</scene>)''
-<Structure load='1ejy' size='300' color='white' frame='true' align='right' caption='Mouse importin α bound to a NLS of a peptide' scene='Sandbox_Reserved_709/Importin_default/1' />
+<Structure load='1ejy' size='350' color='white' frame='true' align='right' caption='Mouse importin α bound to a NLS of a peptide (PDB 1ejy)' scene='Sandbox_Reserved_709/Importin_default/1' />
 '''Importin α''' is a soluble adaptor protein also known as '''karyopherin α'''. Its function is to bind a protein containing a cNLS (''classical Nuclear Localization Signal'') and then to bind an importin β in order to help the import of this protein in the nucleus.
@@ Line 61: / Line 62: @@
 * '''A CAS-binding site.'''
-<scene name='Sandbox_Reserved_709/Importin_default/1'>Back to the default scene</scene>
 ==Importin α : Nup50 complex==
-<Structure load='2c1m' size='300' color='white' frame='true' align='right' scene='Sandbox_Reserved_709/Impnup_default/2' caption='Complex between mouse importin α(70-529) and Nup50(N-ter) />
+<Structure load='2c1m' size='350' color='white' frame='true' align='right' scene='Sandbox_Reserved_709/Impnup_default/2' caption='Mouse importin α:Nup50 complex (PDB 2c1m) />
 ''(<scene name='Sandbox_Reserved_709/Impnup_default/2'>Back to Default scene </scene>)''
+'''Nup50''' (''Nucleoporin 50 kDa'', about 450 aminoacids) is a part of the '''NPCs''', in the '''nucleoplasmic side'''. It is able to bind to <scene name='Sandbox_Reserved_709/Importin/2'>importin importin α</scene> thanks to <scene name='Sandbox_Reserved_709/Nup50/3'>two binding segments</scene> on its N-terminus (''only 46 first aminoacids represented on the structure'').
-Nup50 (''Nucleoporin 50 kDa'', about 450 aminoacids) is a part of the NPCs, in the nucleoplasmic side. It is able to bind to <scene name='Sandbox_Reserved_709/Importin/2'> importin α </scene>thanks to <scene name='Sandbox_Reserved_709/Nup50/3'>two binding segments</scene> on its N-terminus (''only 40 first aminoacids represented on the structure'').
+* The first one (''1-15'') binds to the '''minor NLS binding site''' of importin α. This binding is allowed by the '''two basic aminoacids''' <scene name='Sandbox_Reserved_709/Nup_bindingnls/1'>Lys3 and Arg4</scene> of Nup50. In fact, the positive charge will establish bonds with acidic aminoacids of the NLS binding site, just as an NLS-containing cargo would do. In presence of Nup50, the complex importin α:NLS dissociation rate is higher than the one of spontaneous dissociation : there is a '''competition''' between Nup50 and NLS, whose affinities for the NLS minor binding site are in the same order of magnitude. <ref name ="NUP50"/>
-* The first one (''1-15'') binds to the '''minor NLS binding site''' of importin α. This binding is allowed by the '''two basic aminoacids'''<scene name='Sandbox_Reserved_709/Nup_bindingnls/1'>Lys3 and Arg4</scene> of Nup50. In fact, the positive charge will establish bonds with acidic aminoacids of the NLS binding site, just as an NLS-containing cargo would do. In presence of Nup50, the complex importin α:NLS dissociation rate is higher than the one of spontaneous dissociation : there is a '''competition''' between Nup50 and NLS, whose affinities for the NLS minor binding site are in the same order of magnitude.
+* The second one (''24-46'') binds to the '''C-terminus''' of importin α. Nup50 basic residues 41-46 ('''KKAKRR''') are directed by the formation of '''two turns of an α helix''' (''31-36'' SEEVMK) towards an <scene name='Sandbox_Reserved_709/Nup50_bindingcas/1'>acidic surface</scene> on ARM10. Those electrostatic interactions are essential for the binding of Nup50. Indeed, replacing residues 41-46 by Ala makes the binding undetectable. Furthermore, this binding overlaps the '''CAS''' and the '''Ran binding sites''', explaining why interaction between Nup50 and importin is crucial for building the '''export complex'''.<ref name ="NUP50"/>
-* The second one (''24-46'') binds to the '''C-terminus''' of importin α. Nup50 basic residues 41-46 ('''KKAKRR''') are directed by the formation of two turns of an α helix (''31-36'' SEEVMK) towards an <scene name='Sandbox_Reserved_709/Nup50_bindingcas/1'>acidic surface</scene> on ARM10. Those electrostatic interactions are essential for the binding of Nup50. Indeed, replacing residues 41-46 by Ala makes the binding undetectable. Furthermore, this binding overlaps the CAS and the Ran binding sites, explaining why interaction between Nup50 and importin is crucial for building the export complex.
 The chain between the two binding segments is rich in acidic residues, and seems to work as a flexible linker between those two sites.
@@ Line 95: / Line 93: @@
 [[Category: Mus musculus]]
-[[Category: Matsuura, Y.]]
-[[Category: Stewart, M.]]
 [[Category: Importin-alpha]]
 [[Category: Nuclear protein]]
-[[Category: Nuclear transport-complex]]
-[[Category: Nuclear transport-complex nup50]]
 [[Category: Nucleoporin nup50]]
 [[Category: Protein transport]]
 [[Category: Protein transport-membrane protein complex]]
 [[Category: Protein transport/membrane protein]]
+[[Category: Importin aplpha/karyopherin alpha]]
+[[Category: Protein binding]]
+[[Category: Nucleoplasmin]]
 <ref group="xtra">PMID:22847741</ref><references group="xtra"/>
 <ref group="xtra">PMID:22510057</ref><references group="xtra"/>