?
 
Escherichia coli ApaH and related proteins, metallophosphatase domain ApaH (also known as symmetrically cleaving Ap4A hydrolase and bis(5'nucleosyl)-tetraphosphatase) is a bacterial member of the PPP (phosphoprotein phosphatase) family of serine/threonine phosphatases that hydrolyzes the nucleotide-signaling molecule diadenosine tetraphosphate (Ap(4)A) into two ADP and also hydrolyzes Ap(5)A, Gp(4)G, and other extending compounds. Null mutations in apaH result in high intracellular levels of Ap(4)A which correlate with multiple phenotypes, including a decreased expression of catabolite-repressible genes, a reduction in the expression of flagellar operons, and an increased sensitivity to UV and heat. Ap4A hydrolase is important in responding to heat shock and oxidative stress via regulating the concentration of Ap4A in bacteria. Ap4A hydrolase is also thought to play a role in siderophore production, but the mechanism by which ApaH interacts with siderophore pathways in unknown. The PPP (phosphoprotein phosphatase) family, to which ApaH 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, PrpE, and PrpA/PrpB. 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. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",