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Structural basis of protein phosphatase 2A stable latency.

Jiang L, Stanevich V, Satyshur KA, Kong M, Watkins GR, Wadzinski BE, Sengupta R, Xing Y - Nat Commun (2013)

Bottom Line: This structure suggests that α4 binding to the full-length PP2Ac requires local unfolding near the active site, which perturbs the scaffold subunit binding site at the opposite surface via allosteric relay.These changes stabilize an inactive conformation of PP2Ac and convert oligomeric PP2A complexes to the α4 complex upon perturbation of the active site.Our results show that α4 is a scavenger chaperone that binds to and stabilizes partially folded PP2Ac for stable latency, and reveal a mechanism by which α4 regulates cell survival, and biogenesis and surveillance of PP2A holoenzymes.

View Article: PubMed Central - PubMed

Affiliation: McArdle Laboratory, Department of Oncology, University of Wisconsin-Madison, School of Medicine and Public Health, Madison, Wisconsin 53706, USA.

ABSTRACT
The catalytic subunit of protein phosphatase 2A (PP2Ac) is stabilized in a latent form by α4, a regulatory protein essential for cell survival and biogenesis of all PP2A complexes. Here we report the structure of α4 bound to the N-terminal fragment of PP2Ac. This structure suggests that α4 binding to the full-length PP2Ac requires local unfolding near the active site, which perturbs the scaffold subunit binding site at the opposite surface via allosteric relay. These changes stabilize an inactive conformation of PP2Ac and convert oligomeric PP2A complexes to the α4 complex upon perturbation of the active site. The PP2Ac-α4 interface is essential for cell survival and sterically hinders a PP2A ubiquitination site, important for the stability of cellular PP2Ac. Our results show that α4 is a scavenger chaperone that binds to and stabilizes partially folded PP2Ac for stable latency, and reveal a mechanism by which α4 regulates cell survival, and biogenesis and surveillance of PP2A holoenzymes.

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Characterization of the PP2Ac–α4 interface and displacement of PP2A internal packing.(a) Illustration of the displacement of the loop switch and helix switch between active PP2Ac and the α4 complex. Structural presentations and the colour scheme are the same as in Fig. 2b, except that the loop switch in the partially folded PP2Ac is coloured coral. (b) A close-up view of PP2A internal packing displaced by α4 binding clustered at two arginine centres. Structure presentations and the colour scheme are the same as in a, except that active PP2Ac is shown in ribbon. Residues from active PP2Ac are in ball-and-stick and coloured grey. (c) A close-up view of the PP2Ac–α4 interface involving regions of PP2A internal packing and direct contacts with PP2A surface residues at two periphery interfaces (inlets). The structural orientation is the same as in b. The nPP2Ac and α4 are in ribbon and worm, respectively. Residues of α4 and nPP2Ac are in ball-and-stick and cylinder and coloured green and yellow, respectively.
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f4: Characterization of the PP2Ac–α4 interface and displacement of PP2A internal packing.(a) Illustration of the displacement of the loop switch and helix switch between active PP2Ac and the α4 complex. Structural presentations and the colour scheme are the same as in Fig. 2b, except that the loop switch in the partially folded PP2Ac is coloured coral. (b) A close-up view of PP2A internal packing displaced by α4 binding clustered at two arginine centres. Structure presentations and the colour scheme are the same as in a, except that active PP2Ac is shown in ribbon. Residues from active PP2Ac are in ball-and-stick and coloured grey. (c) A close-up view of the PP2Ac–α4 interface involving regions of PP2A internal packing and direct contacts with PP2A surface residues at two periphery interfaces (inlets). The structural orientation is the same as in b. The nPP2Ac and α4 are in ribbon and worm, respectively. Residues of α4 and nPP2Ac are in ball-and-stick and cylinder and coloured green and yellow, respectively.

Mentions: The helix and loop switch directly contact each other and fold against the N-terminal helix motif in active PP2Ac (PDB accession code: 2IE3)22 (Fig. 4a). The underlying internal packing required for α4 binding is clustered at two arginine centres (Fig. 4b). At the first arginine centre of active PP2Ac, Arg185 in loop switch makes extensive intramolecular H-bond interactions to the backbone carbonyl groups of residues 40, 42 and 152 and the sidechain of Asn44, buttressed by hydrophobic contacts made by Leu186 in loop switch to Thr40 and Tyr152. In the nPP2Ac–α4 complex, Arg155 of α4 occupies the same position as Arg185 in PP2A loop switch, making similar intermolecular contacts, and Ile159 of α4 replaces internal hydrophobic contacts of Leu186 in PP2A loop switch and forms intermolecular contacts to the same PP2Ac residues (Fig. 4b). At the second arginine centre of active PP2Ac, Arg121 in helix switch makes extensive intramolecular H-bond and salt-bridge interactions to three acidic residues, Asp148, Asp151, and Glu188, buttressed by an H-bond formed by Thr122 and Trp143 (Fig. 4b). Arg121 also interacts with Glu188, contributing to internal packing between helix (Arg121) and loop switch (Glu188) (Fig. 4b). Relaxation of helix switch disrupts the internal packing of Arg121 and allows similar intermolecular H-bond and salt-bridge network to be formed between Lys158 of α4 and Asp148/151 of PP2Ac (Fig. 4c). It also allows van der Waals contacts between Trp143 of PP2Ac and at least four residues in α4 (Fig. 4c).


Structural basis of protein phosphatase 2A stable latency.

Jiang L, Stanevich V, Satyshur KA, Kong M, Watkins GR, Wadzinski BE, Sengupta R, Xing Y - Nat Commun (2013)

Characterization of the PP2Ac–α4 interface and displacement of PP2A internal packing.(a) Illustration of the displacement of the loop switch and helix switch between active PP2Ac and the α4 complex. Structural presentations and the colour scheme are the same as in Fig. 2b, except that the loop switch in the partially folded PP2Ac is coloured coral. (b) A close-up view of PP2A internal packing displaced by α4 binding clustered at two arginine centres. Structure presentations and the colour scheme are the same as in a, except that active PP2Ac is shown in ribbon. Residues from active PP2Ac are in ball-and-stick and coloured grey. (c) A close-up view of the PP2Ac–α4 interface involving regions of PP2A internal packing and direct contacts with PP2A surface residues at two periphery interfaces (inlets). The structural orientation is the same as in b. The nPP2Ac and α4 are in ribbon and worm, respectively. Residues of α4 and nPP2Ac are in ball-and-stick and cylinder and coloured green and yellow, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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f4: Characterization of the PP2Ac–α4 interface and displacement of PP2A internal packing.(a) Illustration of the displacement of the loop switch and helix switch between active PP2Ac and the α4 complex. Structural presentations and the colour scheme are the same as in Fig. 2b, except that the loop switch in the partially folded PP2Ac is coloured coral. (b) A close-up view of PP2A internal packing displaced by α4 binding clustered at two arginine centres. Structure presentations and the colour scheme are the same as in a, except that active PP2Ac is shown in ribbon. Residues from active PP2Ac are in ball-and-stick and coloured grey. (c) A close-up view of the PP2Ac–α4 interface involving regions of PP2A internal packing and direct contacts with PP2A surface residues at two periphery interfaces (inlets). The structural orientation is the same as in b. The nPP2Ac and α4 are in ribbon and worm, respectively. Residues of α4 and nPP2Ac are in ball-and-stick and cylinder and coloured green and yellow, respectively.
Mentions: The helix and loop switch directly contact each other and fold against the N-terminal helix motif in active PP2Ac (PDB accession code: 2IE3)22 (Fig. 4a). The underlying internal packing required for α4 binding is clustered at two arginine centres (Fig. 4b). At the first arginine centre of active PP2Ac, Arg185 in loop switch makes extensive intramolecular H-bond interactions to the backbone carbonyl groups of residues 40, 42 and 152 and the sidechain of Asn44, buttressed by hydrophobic contacts made by Leu186 in loop switch to Thr40 and Tyr152. In the nPP2Ac–α4 complex, Arg155 of α4 occupies the same position as Arg185 in PP2A loop switch, making similar intermolecular contacts, and Ile159 of α4 replaces internal hydrophobic contacts of Leu186 in PP2A loop switch and forms intermolecular contacts to the same PP2Ac residues (Fig. 4b). At the second arginine centre of active PP2Ac, Arg121 in helix switch makes extensive intramolecular H-bond and salt-bridge interactions to three acidic residues, Asp148, Asp151, and Glu188, buttressed by an H-bond formed by Thr122 and Trp143 (Fig. 4b). Arg121 also interacts with Glu188, contributing to internal packing between helix (Arg121) and loop switch (Glu188) (Fig. 4b). Relaxation of helix switch disrupts the internal packing of Arg121 and allows similar intermolecular H-bond and salt-bridge network to be formed between Lys158 of α4 and Asp148/151 of PP2Ac (Fig. 4c). It also allows van der Waals contacts between Trp143 of PP2Ac and at least four residues in α4 (Fig. 4c).

Bottom Line: This structure suggests that α4 binding to the full-length PP2Ac requires local unfolding near the active site, which perturbs the scaffold subunit binding site at the opposite surface via allosteric relay.These changes stabilize an inactive conformation of PP2Ac and convert oligomeric PP2A complexes to the α4 complex upon perturbation of the active site.Our results show that α4 is a scavenger chaperone that binds to and stabilizes partially folded PP2Ac for stable latency, and reveal a mechanism by which α4 regulates cell survival, and biogenesis and surveillance of PP2A holoenzymes.

View Article: PubMed Central - PubMed

Affiliation: McArdle Laboratory, Department of Oncology, University of Wisconsin-Madison, School of Medicine and Public Health, Madison, Wisconsin 53706, USA.

ABSTRACT
The catalytic subunit of protein phosphatase 2A (PP2Ac) is stabilized in a latent form by α4, a regulatory protein essential for cell survival and biogenesis of all PP2A complexes. Here we report the structure of α4 bound to the N-terminal fragment of PP2Ac. This structure suggests that α4 binding to the full-length PP2Ac requires local unfolding near the active site, which perturbs the scaffold subunit binding site at the opposite surface via allosteric relay. These changes stabilize an inactive conformation of PP2Ac and convert oligomeric PP2A complexes to the α4 complex upon perturbation of the active site. The PP2Ac-α4 interface is essential for cell survival and sterically hinders a PP2A ubiquitination site, important for the stability of cellular PP2Ac. Our results show that α4 is a scavenger chaperone that binds to and stabilizes partially folded PP2Ac for stable latency, and reveal a mechanism by which α4 regulates cell survival, and biogenesis and surveillance of PP2A holoenzymes.

Show MeSH