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Crystal structure of a protein phosphatase 2A heterotrimeric holoenzyme


Protein phosphatase 2A (PP2A) is a principal Ser/Thr phosphatase, the deregulation of which is associated with multiple human cancers, Alzheimer’s disease and increased susceptibility to pathogen infections. How PP2A is structurally organized and functionally regulated remains unclear. Here we report the crystal structure of an AB′C heterotrimeric PP2A holoenzyme. The structure reveals that the HEAT repeats of the scaffold A subunit form a horseshoe-shaped fold, holding the catalytic C and regulatory B′ subunits together on the same side. The regulatory B′ subunit forms pseudo-HEAT repeats and interacts with the C subunit near the active site, thereby defining substrate specificity. The methylated carboxy-terminal tail of the C subunit interacts with a highly negatively charged region at the interface between A and B′ subunits, suggesting that the C-terminal carboxyl methylation of the C subunit promotes B′ subunit recruitment by neutralizing charge repulsion. Together, our structural results establish a crucial foundation for understanding PP2A assembly, substrate recruitment and regulation.

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Figure 1: Overall structure of the Aα–B56γ1–Cα heterotrimeric PP2A holoenzyme.
Figure 2: Structures of the scaffold A subunit, the catalytic Cα subunit and the A–C interface.
Figure 3: Overall structure of the regulatory B56γ1 subunit and the A–B interface.
Figure 4: Interface of the catalytic Cα subunit with the regulatory B56γ1.
Figure 5: Interactions between the methylated C-terminal tail of the catalytic Cα subunit and the A–B interface.


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We thank S. Morrone, F. Gao and other laboratory members and rotation students for help with this work. We are grateful to J. Abendroth for advice on crystallographic computation, and the staff at ALS beamline 5.0.2 for assistance with data collection. We also thank D. Virshup and X. Liu for B56 cDNAs, and N. Zheng, D. Virshup and E. Ogris for critical comments on this manuscript. This work was supported in part by an Investigator’s Award from the Burroughs Welcome Fund to W.X. and by the Keck Center for Pathogenesis at the University of Washington.

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Correspondence to Wenqing Xu.

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Coordinates and structure factors are deposited in the Protein Data Bank under accession code 2IAE. Reprints and permissions information is available at The authors declare no competing financial interests.

Supplementary information

Supplementary Notes

This file contains the Supplementary Methods, Supplementary Figures 1–9 and additional references. The Supplementary Methods describes the detailed methods of protein purification, crystallization, and structural determination. (PDF 1006 kb)

Supplementary Table

This table contains the summary of crystallographic analysis. (PDF 345 kb)

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Cho, U., Xu, W. Crystal structure of a protein phosphatase 2A heterotrimeric holoenzyme. Nature 445, 53–57 (2007).

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