Sandbox Reserved 709: Difference between revisions

(10 intermediate revisions by the same user not shown)

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:

===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.

Line 52:

Line 53:

Here, as the structure begins at the amino acid number 70, we cannot see the IBB which is located in the 2-60 region.

* '''A 50kDa C-terminal''' <scene name='Sandbox_Reserved_709/Importin_nlsbs/1'>NLS binding sites</scene> contained in <scene name='Sandbox_Reserved_709/Importin_arm/3'>10 tandem armadillo (Arm) repeats</scene>. These arm repeat domains have an elongated superhelical structure and each of them contains 3 α-helices (H1, H2, H3). Together, H3 helices define the inner concave surface of the protein and the NLS-binding site. The main chain of the cNLs runs antiparallel to the direction of the importin α superhelix, with the cNLS backbone interacting with an array of conserved asparagine residues in consecutive Arm repeats on the importin α surface.In fact there are two NLS-binding sites : a major one and a minor one. Thus, monopartite cNLSs are able to bind at two distinct sites on importin α (with a preference for the major site). Bipartite cNLSs simultaneously interact with both binding sites, with the larger C-terminal basic cluster binding to the major site (located in Arm repeats 2-4) and the smaller upstream cluster binding to the minor site (located in Arm repeats 6-8).<ref>PMID:22248489</ref>

* '''A 50kDa C-terminal''' <scene name='Sandbox_Reserved_709/Importin_nlsbs/2'>NLS binding sites</scene> contained in <scene name='Sandbox_Reserved_709/Importin_arm/5'>10 tandem armadillo (Arm) repeats</scene>. These arm repeat domains have an elongated superhelical structure and each of them contains 3 α-helices (H1, H2, H3). Together, H3 helices define the inner concave surface of the protein and the NLS-binding site. The main chain of the cNLs runs antiparallel to the direction of the importin α superhelix, with the cNLS backbone interacting with an array of conserved asparagine residues in consecutive Arm repeats on the importin α surface.In fact there are two NLS-binding sites : a major one and a minor one. Thus, monopartite cNLSs are able to bind at two distinct sites on importin α (with a preference for the major site). Bipartite cNLSs simultaneously interact with both binding sites, with the larger C-terminal basic cluster binding to the major site (located in Arm repeats 2-4) and the smaller upstream cluster binding to the minor site (located in Arm repeats 6-8).<ref>PMID:22248489</ref>

Here you can see a <scene name='Sandbox_Reserved_709/Nls_basic/1'>NLS </scene>bound to the NLS-binding site of importin α.

Here you can see a <scene name='Sandbox_Reserved_709/Nls_basic/2'>NLS </scene>bound to the NLS-binding site of importin α.

* '''A NLS'''. Thus, importin α belongs to the group of proteins containing both a ligand (NLS) and a cognate receptor (NLS-binding site). That’s why it could have a possibility of autologous ligand-receptor interactions. Nevertheless, it has been shown that NLS of importin α overlaps with the IBB. Thereby, binding of importin β to importin α covers the NLS of importin α preventing autologous ligand receptor interactions. <ref>PMID:8692858</ref>

Line 62:

Line 63:

* '''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'').

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

~~==Importin α : Nup50 complex==~~

~~<Structure load='2c1m' size='300' color='white' frame='true' align='right' caption='Complex between mouse importin α(residues 70-529) and Nup50(or Npap60)' />~~

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/1'> importin α</scene>thanks to its <scene name='Sandbox_Reserved_709/Nup50/1'>N-terminal domain</scene> (''only represented on the structure''). There are two binding sites for Nup50 on importin α :

* The first one overlaps with the minor NLS binding site. The affinity of Nup50 for this site is... <scene name='Sandbox_Reserved_709/Nup_bindingnls/1'>Lys3 and Arg4</scene>

==See Also==

Line 85:

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]]

Sandbox Reserved 709: Difference between revisions

Navigation menu

Page actions

Page actions

Personal tools

Navigation

Search

Tools

@@ 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 52: / Line 53: @@
 Here, as the structure begins at the amino acid number 70, we cannot see the IBB which is located in the 2-60 region.
-* '''A 50kDa C-terminal''' <scene name='Sandbox_Reserved_709/Importin_nlsbs/1'>NLS binding sites</scene> contained in <scene name='Sandbox_Reserved_709/Importin_arm/3'>10 tandem armadillo (Arm) repeats</scene>. These arm repeat domains have an elongated superhelical structure and each of them contains 3 α-helices (H1, H2, H3). Together, H3 helices define the inner concave surface of the protein and the NLS-binding site.  The main chain of the cNLs runs antiparallel to the direction of the importin α superhelix, with the cNLS backbone interacting with an array of conserved asparagine residues in consecutive Arm repeats on the importin α surface.In fact there are two NLS-binding sites : a major one and a minor one. Thus, monopartite cNLSs are able to bind at two distinct sites on importin α (with a preference for the major site). Bipartite cNLSs simultaneously interact with both binding sites, with the larger C-terminal basic cluster binding to the major site (located in Arm repeats 2-4) and the smaller upstream cluster binding to the minor site (located in Arm repeats 6-8).<ref>PMID:22248489</ref>
+* '''A 50kDa C-terminal''' <scene name='Sandbox_Reserved_709/Importin_nlsbs/2'>NLS binding sites</scene> contained in <scene name='Sandbox_Reserved_709/Importin_arm/5'>10 tandem armadillo (Arm) repeats</scene>. These arm repeat domains have an elongated superhelical structure and each of them contains 3 α-helices (H1, H2, H3). Together, H3 helices define the inner concave surface of the protein and the NLS-binding site.  The main chain of the cNLs runs antiparallel to the direction of the importin α superhelix, with the cNLS backbone interacting with an array of conserved asparagine residues in consecutive Arm repeats on the importin α surface.In fact there are two NLS-binding sites : a major one and a minor one. Thus, monopartite cNLSs are able to bind at two distinct sites on importin α (with a preference for the major site). Bipartite cNLSs simultaneously interact with both binding sites, with the larger C-terminal basic cluster binding to the major site (located in Arm repeats 2-4) and the smaller upstream cluster binding to the minor site (located in Arm repeats 6-8).<ref>PMID:22248489</ref>
-Here you can see a <scene name='Sandbox_Reserved_709/Nls_basic/1'>NLS </scene>bound to the NLS-binding site of importin α.
+Here you can see a <scene name='Sandbox_Reserved_709/Nls_basic/2'>NLS </scene>bound to the NLS-binding site of importin α.
 * '''A NLS'''. Thus, importin α belongs to the group of proteins containing both a ligand (NLS) and a cognate receptor (NLS-binding site). That’s why it could have a possibility of autologous ligand-receptor interactions. Nevertheless, it has been shown that NLS of importin α overlaps with the IBB. Thereby, binding of importin β to importin α covers the NLS of importin α preventing autologous ligand receptor interactions. <ref>PMID:8692858</ref>
@@ Line 62: / Line 63: @@
 * '''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='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'').
+* 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 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 chain between the two binding segments is rich in acidic residues, and seems to work as a flexible linker between those two sites.
-==Importin α : Nup50 complex==
-<Structure load='2c1m' size='300' color='white' frame='true' align='right' caption='Complex between mouse importin α(residues 70-529) and Nup50(or Npap60)' />
-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/1'> importin α</scene>thanks to its <scene name='Sandbox_Reserved_709/Nup50/1'>N-terminal domain</scene> (''only represented on the structure''). There are two binding sites for Nup50 on importin α :
-* The first one overlaps with the minor NLS binding site. The affinity of Nup50 for this site is... <scene name='Sandbox_Reserved_709/Nup_bindingnls/1'>Lys3 and Arg4</scene>
 ==See Also==
@@ Line 85: / 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"/>