Plays a role in activating the myosin contractile function. Dephosphorylates threonine at 'Thr-1823', 'Thr-1833' and 'Thr-2029' in the C-terminal tail region of myosin II heavy chain (mhcA). Drives the assembly of dephosphorylated myosin II filaments to allow myosin recruitment into the cytoskeleton. 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. PP2A consists of a trimeric holoenzyme, composed of a 37 kDa catalytic subunit (C subunit) and a 65 kDa constant regulatory subunit (A subunit), that associates with a variety of regulatory subunits (B subunit) such as phr2AB (B55) and psrA (B56 homolog). The trimer may partially dissociates into a core 'AC' dimer equally active compared to the trimer. Reversibly methyl esterified on Leu-306 by leucine carboxyl methyltransferase 1 (LCMT) 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-2A subfamily.