PP1, PPKL (PP1 and kelch-like) enzymes, and related proteins, metallophosphatase domain
PP1 (protein phosphatase type 1) is a serine/threonine phosphatase that regulates many cellular processes including: cell-cycle progression, protein synthesis, muscle contraction, carbohydrate metabolism, transcription and neuronal signaling, through its interaction with at least 180 known targeting proteins. PP1 occurs in all tissues and regulates many pathways, ranging from cell-cycle progression to carbohydrate metabolism. Also included here are the PPKL (PP1 and kelch-like) enzymes including the PPQ, PPZ1, and PPZ2 fungal phosphatases. These PPKLs have a large N-terminal kelch repeat in addition to a C-terminal phosphoesterase domain. The PPP (phosphoprotein phosphatase) family, to which PP1 belongs, is one of two known protein phosphatase families specific for serine and threonine. The PPP family also includes: PP2A, PP2B (calcineurin), PP4, PP5, PP6, PP7, Bsu1, RdgC, PrpE, PrpA/PrpB, and ApA4 hydrolase. The PPP catalytic domain is defined by three conserved motifs (-GDXHG-, -GDXVDRG- and -GNHE-). The PPP enzyme family is ancient with members found in all eukaryotes, and in most bacterial and archeal genomes. Dephosphorylation of phosphoserines and phosphothreonines on target proteins plays a central role in the regulation of many cellular processes. PPPs belong to the metallophosphatase (MPP) superfamily. MPPs are functionally diverse, but all share a conserved domain with an active site consisting of two metal ions (usually manganese, iron, or zinc) coordinated with octahedral geometry by a cage of histidine, aspartate, and asparagine residues. The MPP superfamily includes: Mre11/SbcD-like exonucleases, Dbr1-like RNA lariat debranching enzymes, YfcE-like phosphodiesterases, purple acid phosphatases (PAPs), YbbF-like UDP-2,3-diacylglucosamine hydrolases, and acid sphingomyelinases (ASMases). The conserved domain is a double beta-sheet sandwich with a di-metal active site made up of residues located at the C-terminal side of the sheets. This domain is thought to allow for productive metal coordination.
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