Carboxyl methylation regulates phosphoprotein phosphatase 2A by controlling the association of regulatory B subunits

Phosphoprotein phosphatase 2a (PP2a) is a major phosphoserine/threonine protein phosphatase in all eukaryotes. It has been isolated as a heterotrimeric holoenzyme composed of a 65 kDa A subunit, which serves as a scaffold for the association of the 36 kDa catalytic C subunit, and a variety of B subunits that control phosphatase specificity. The C subunit is reversibly methyl esterified by specific methyltransferase and methylesterase enzymes at a completely conserved C-terminal leucine residue. Here we show that methylation plays an essential role in promoting PP2a holoenzyme assembly and that demethylation has an opposing effect. Changes in methylation indirectly regulate PP2a phosphatase activity by controlling the binding of regulatory B subunits to AC dimers.