Bacillus subtilis PrpE and related proteins, metallophosphatase domain
PrpE (protein phosphatase E) is a bacterial member of the PPP (phosphoprotein phosphatase) family of serine/threonine phosphatases and a key signal transduction pathway component controlling the expression of spore germination receptors GerA and GerK in Bacillus subtilis. PrpE is closely related to ApaH (also known symmetrical Ap(4)A hydrolase and bis(5'nucleosyl)-tetraphosphatase). PrpE has specificity for phosphotyrosine only, unlike the serine/threonine phosphatases to which it is related. The Bacilli members of this family are single domain proteins while the other members have N- and C-terminal domains in addition to this phosphatase domain. Pnkp is the end-healing and end-sealing component of an RNA repair system present in bacteria. It is composed of three catalytic modules: an N-terminal polynucleotide 5' kinase, a central 2',3' phosphatase, and a C-terminal ligase. Pnkp is a Mn(2+)-dependent phosphodiesterase-monoesterase that dephosphorylates 2',3'-cyclic phosphate RNA ends. An RNA binding site is suggested by a continuous tract of positive surface potential flanking the active site. The PPP (phosphoprotein phosphatase) family, to which PrpE belongs, is one of two known protein phosphatase families specific for serine and threonine. The PPP family also includes: PP1, PP2A, PP2B (calcineurin), PP4, PP5, PP6, PP7, Bsu1, RdgC, 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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