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polynucleotide 3'-phosphatase domain similar to the phosphatase domain of the bifunctional enzyme polynucleotide 5'-kinase/3'-phosphatase Polynucleotide 3'-phosphatase (PNP) domain. This domain dephosphorylates single-stranded as well as double-stranded 3'-phospho termini. It is found in bifunctional enzyme polynucleotide kinase/phosphatase (PNKP) which contain both kinase and phosphatase domains. PNKP plays a key role in both base excision repair and non-homologous end-joining DNA repair pathway. DNA strand breaks can result from DNA damage by ionizing radiation and chemical agents, such as alkylating agents or anticancer agents. Such DNA damage often results in DNA strands with 5'-hydroxyl and 3'-phosphate termini. However, the repair of DNA damage by DNA polymerases and ligases requires 5'-phosphate and 3'-hydroxyl termini. PNKP acts as a 5'-kinase/3'-phosphatase to create 5'-phosphate/3'-hydroxyl termini, which are a necessary prerequisite for ligation during repair. This family belongs to the haloacid dehalogenase-like (HAD) hydrolases, a large superfamily of diverse enzymes that catalyze carbon or phosphoryl group transfer reactions on a range of substrates, using an active site aspartate in nucleophilic catalysis. Members of this superfamily include 2-L-haloalkanoic acid dehalogenase, azetidine hydrolase, phosphonoacetaldehyde hydrolase, phosphoserine phosphatase, phosphomannomutase, P-type ATPases and many others. HAD hydrolases are found in all three kingdoms of life, and most genomes are predicted to contain multiple HAD-like proteins. Members possess a highly conserved alpha/beta core domain, and many also possess a small cap domain, the fold and function of which is variable. HAD hydrolases are sometimes referred to as belonging to the DDDD superfamily of phosphohydrolases. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",