Protein phosphatase 2

[4] Its serine/threonine phosphatase activity has a broad substrate specificity and diverse cellular functions.

Among the targets of PP2A are proteins of oncogenic signaling cascades, such as Raf, MEK, and AKT, where PP2A may act as a tumor suppressor.

The A subunit, a founding member of the HEAT repeat protein family (huntingtin, EF3, PP2A, TOR1), is the scaffold required for the formation of the heterotrimeric complex.

Multicellular eukaryotes express four classes of variable regulatory subunits: B (PR55), B′ (B56 or PR61), B″ (PR72), and B‴ (PR93/PR110), with at least 16 members in these subfamilies.

In addition, accessory proteins and post-translational modifications (such as methylation) control PP2A subunit associations and activities.

The assembled heterotrimer of protein phosphatase 2A. The structural subunit A, consisting of 15 HEAT repeats , is shown in rainbow color with the N-terminus in blue at bottom and the C-terminus in red at top. The regulatory subunit B (B' gamma), consisting of irregular pseudo-HEAT repeats, is shown in light blue. The catalytic subunit C is shown in tan. (All from PDB : 2IAE ​.) Superposed is the unbound form of the regulatory subunit A in gray (from PDB : 1B3U ​), illustrating the flexibility of this alpha solenoid protein. Conformational changes in HEAT repeat 11 result in flexing the C-terminal end of the protein to accommodate binding of the catalytic subunit. [ 1 ] [ 5 ]