haloacid dehalogenase (HAD)-like 5'-nucleotidases similar to human cytosolic IIIA and IIIB
5'-nucleotidases dephosphorylate nucleoside 5prime-monophosphates. This family includes human 5'-nucleotidase, cytosolic IIIA (cN-IIIA, previously called cN-III; NT5C3A) the main pyrimidine 5'-nucleotidase in erythrocytes which dephosphorylates the pyrimidine nucleotides CMP, UMP, TMP, and the purine 7-methylguanosine monophosphate (m7GM), and possesses phosphotransferase activity. It also includes human 5'-nucleotidase, cytosolic IIIB (cN-IIIB; NT5C3B) which has a strong preference for m7GMP, dephosphorylates CMP and UMP and, with significantly lower efficiency, GMP and AMP, and can also act as a phosphotransferase. 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.