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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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Overall structure of the nPP2Ac–α4 complex.(a) Overall structure of the nPP2Ac–α4 complex and the symmetry-related heterodimer in ribbon. The nPP2Ac, α4 and their symmetry-related counterparts are coloured blue, magenta, green, and orange, respectively. (b) Structural overlay of the nPP2Ac–α4 complex and the active PP2A catalytic subunit (PDB accession code: 2IE3) by the N-terminal helix motif. The colour scheme is the same as in a, except that active PP2Ac is coloured cyan and the helix and loop switches are coloured yellow. Helices and β-strands are shown in tube and ribbon, respectively. α4 is shown in semi-transparent surface. Only helix 5 and 6 of α4 are shown in tube. Red spheres represent catalytic metal ions in active PP2Ac.
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f2: Overall structure of the nPP2Ac–α4 complex.(a) Overall structure of the nPP2Ac–α4 complex and the symmetry-related heterodimer in ribbon. The nPP2Ac, α4 and their symmetry-related counterparts are coloured blue, magenta, green, and orange, respectively. (b) Structural overlay of the nPP2Ac–α4 complex and the active PP2A catalytic subunit (PDB accession code: 2IE3) by the N-terminal helix motif. The colour scheme is the same as in a, except that active PP2Ac is coloured cyan and the helix and loop switches are coloured yellow. Helices and β-strands are shown in tube and ribbon, respectively. α4 is shown in semi-transparent surface. Only helix 5 and 6 of α4 are shown in tube. Red spheres represent catalytic metal ions in active PP2Ac.

Mentions: The structure of the nPP2Ac–α4 complex showed that a pair of widely opened helix tweezers formed by helix 5 and 6 in α4, 45 Å and 55 Å in length, respectively, clamp onto the ends of the helix motif of nPP2Ac (Fig. 2a). The α4 helix tweezers are more open in the α4 apo-structure21, but adopt a relatively closed conformation by interaction with nPP2Ac. Little change is observed for the PP2Ac helix motif compared with active PP2Ac, suggesting that folding of this helix motif remains intact in the partially folded PP2Ac. One of the helices (C63–69) is relaxed into an extended strand, likely induced by crystal packing (Fig. 2a).


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)

Overall structure of the nPP2Ac–α4 complex.(a) Overall structure of the nPP2Ac–α4 complex and the symmetry-related heterodimer in ribbon. The nPP2Ac, α4 and their symmetry-related counterparts are coloured blue, magenta, green, and orange, respectively. (b) Structural overlay of the nPP2Ac–α4 complex and the active PP2A catalytic subunit (PDB accession code: 2IE3) by the N-terminal helix motif. The colour scheme is the same as in a, except that active PP2Ac is coloured cyan and the helix and loop switches are coloured yellow. Helices and β-strands are shown in tube and ribbon, respectively. α4 is shown in semi-transparent surface. Only helix 5 and 6 of α4 are shown in tube. Red spheres represent catalytic metal ions in active PP2Ac.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3644067&req=5

f2: Overall structure of the nPP2Ac–α4 complex.(a) Overall structure of the nPP2Ac–α4 complex and the symmetry-related heterodimer in ribbon. The nPP2Ac, α4 and their symmetry-related counterparts are coloured blue, magenta, green, and orange, respectively. (b) Structural overlay of the nPP2Ac–α4 complex and the active PP2A catalytic subunit (PDB accession code: 2IE3) by the N-terminal helix motif. The colour scheme is the same as in a, except that active PP2Ac is coloured cyan and the helix and loop switches are coloured yellow. Helices and β-strands are shown in tube and ribbon, respectively. α4 is shown in semi-transparent surface. Only helix 5 and 6 of α4 are shown in tube. Red spheres represent catalytic metal ions in active PP2Ac.
Mentions: The structure of the nPP2Ac–α4 complex showed that a pair of widely opened helix tweezers formed by helix 5 and 6 in α4, 45 Å and 55 Å in length, respectively, clamp onto the ends of the helix motif of nPP2Ac (Fig. 2a). The α4 helix tweezers are more open in the α4 apo-structure21, but adopt a relatively closed conformation by interaction with nPP2Ac. Little change is observed for the PP2Ac helix motif compared with active PP2Ac, suggesting that folding of this helix motif remains intact in the partially folded PP2Ac. One of the helices (C63–69) is relaxed into an extended strand, likely induced by crystal packing (Fig. 2a).

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