Protein phosphatase that regulates many processes such as microtubule organization at centrosomes. The probable PP4 complex Pp4-19C-PPP4R2r-flfl (PPP4C-PPP4R2-PPP4R3) is required to prevent caspase-induced cell death (in vitro). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 manganese ions per subunit. Serine/threonine-protein phosphatase 4 (PP4) occurs in different assemblies of the catalytic and one or more regulatory subunits (By similarity). Probably part of a PP4 PPP4C-PPP4R2-PPP4R3 complex containing Pp4-19C, PPP4R2r and flfl. Reversibly methyl esterified on Leu-307 by leucine carboxyl methyltransferase 1 (LCMT1) and protein phosphatase methylesterase 1 (PPME1). Carboxyl methylation influences the affinity of the catalytic subunit for the different regulatory subunits, thereby modulating the PP2A holoenzyme's substrate specificity, enzyme activity and cellular localization (By similarity). Belongs to the PPP phosphatase family. PP-4 (PP-X) subfamily.