Phosphatase Families Dephosphorylating Serine and Threonine Residues in Proteins

Publisher Summary Protein serine/threonine phosphatases are enzymes that reverse the actions of protein kinases by cleaving phosphate from serine and threonine residues in proteins. They are structurally distinct from the superfamily of protein phosphatases, and also functionally distinct from the acid and alkaline phosphatases that cleave phosphate from other molecules. The current classification of protein serine/threonine phosphatases is based upon the amino acid sequences of the catalytic subunits, which fall into three families. The two major families have been termed the phosphoprotein phosphatase (PPP) family, of which the prototypic member is Ppp1c/PP1, and the protein phosphatase, Mg 2+ /Mn 2+ -dependent (PPM) family, of which the prototypic member is Ppm1c/PP2C. The three-dimensional structures of the catalytic subunits and mechanism of catalysis of these families show some similarities, suggesting that the two families may have undergone convergent evolution. Members of the PPP family of protein phosphatases are widely distributed in all eukaryotic phyla. The regulatory subunits or interactors of Ppp1c include regulatory proteins, phosphatase inhibitor proteins, and proteins originally identified by their own intrinsic properties or functions, such as the retinomablastoma protein (Rb). Ppp1 complexes in mammals regulate functions as disparate as glycogen metabolism, muscle contraction, protein synthesis (transcription, mRNA processing, and translation), signal transduction via receptors and ion channels, cell cycle progression, and apoptosis. Identifying all their functions may uncover promising drug targets among the largely pharmacologically untapped protein serine/threonine phosphatases.