PP7, metallophosphatase domainPP7 is a plant phosphoprotein phosphatase that is highly expressed in a subset of stomata and thought to play an important role in sensory signaling. PP7 acts as a positive regulator of signaling downstream of cryptochrome blue light photoreceptors. PP7 also controls amplification of phytochrome signaling, and interacts with nucleotidediphosphate kinase 2 (NDPK2), a positive regulator of phytochrome signalling. In addition, PP7 interacts with heat shock transcription factor HSF and up-regulates protective heat shock proteins. PP7 may also play a role in salicylic acid-dependent defense signaling. The PPP (phosphoprotein phosphatase) family, to which PP7 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, 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.