PP2A

Protein Phosphatase 2A (PP2A), a heterotrimeric protein phosphatase, is a ubiquitous and conserved Serine/Threonine phosphatase with broad substrate specificity and diverse cellular functions. PP2A comprises A and B subunits which are regulatory and a catalytic C subunit. When the PP2A catalytic C subunit associates with the regulatory A and B subunits several species of holoenzymes are produced with distinct functions and characteristics. The A subunit, a founding member of the HEAT repeat protein family (huntington-elongation-A subunit-TOR), is the scaffold required for the formation of the heterotrimeric complex. When the A subunit binds it alters the enzymatic activity of the catalytic subunit, even if the B subunit is absent. While C and A subunit sequences show remarkable sequence conservation throughout eukaryotes, regulatory B subunits are more heterogeneous and are believed to play key roles in controlling the localization and specific activity of different holoenzymes. Multicellular eukaryotes express four classes of variable regulatory subunits: B (PR55), Bˈ (B56 or PR61), Bˈˈ (PR72), and Bˈˈˈ (PR93/PR110), with at least 16 members in these subfamilies. In Addition, accessory proteins and posttranslational modifications (such as methylation) control PP2A subunit associations and activities.

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The two catalytic metal ions located at bottom of PP2A's active site have been recently identified as manganese, which had previously been suggested as potential candidates.

References

• Xu Y, Xing Y, Chen Y, et al (2006). "Structure of the protein phosphatase 2A holoenzyme". Cell 127 (6): 1239-51. doi:10.1016/j.cell.2006.11.033. PMID 17174897.

• Xing Y, Xu Y, Chen Y, et al (2006). "Structure of protein phosphatase 2A core enzyme bound to tumor-inducing toxins". Cell 127 (2): 341-53. doi:10.1016/j.cell.2006.09.025. PMID 17055435.