Protein phosphatase 2A (PP2A) removes the serine- or threonine-bound phosphate group from a wide range of phosphoproteins. The enzyme is very versatile owing to a large number of regulatory subunits and its ability to interact with numerous other proteins. The PP2A holoenzyme is a dimeric or trimeric protein built up from a catalytic subunit (PP2AC) (catalytic subunit of PP2A), a second constant regulatory subunit, and a third variable subunit. Three major classes of third subunits are currently described. Each of the three subunits of PP2A exists in at least two isoforms, thereby leading to a great variety of possible holoenzyme conformations, all with potential different substrate affinities and catalytic activities.
The common heterodimeric core of the human enzyme consists of PPP2CA, a 36 kDa catalytic subunit, and PPP2R1A, a 65 kDa constant regulatory subunit. The regulatory subunit exists as two closely related isoforms designated Aα and Aβ [Zhou03b]. The dimer can associate with a variety of additional regulatory subunits.
Zhou03b: Zhou J, Pham HT, Ruediger R, Walter G (2003). "Characterization of the Aalpha and Abeta subunit isoforms of protein phosphatase 2A: differences in expression, subunit interaction, and evolution." Biochem J 369(Pt 2);387-98. PMID: 12370081
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