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molecular class C acid phosphatases, similar to Haemophilus influenzae e (P4) acid phosphatase; belongs to the haloacid dehalogenase-like hydrolase superfamily Molecular class C acid phosphatases (CAPs) are nonspecific acid phosphatases with generally broad substrate specificity and optimum activity at neutral to acidic pH. Members include Haemophilus influenzae lipoprotein e (P4), Elizabethkingia meningosepticum OlpA, Helicobacter pylori HppA, Enterobacter sp. 4 acid phosphatase PhoI, and Streptococcus pyogenes M1 GAS LppC. Lipoprotein e (P4) exhibits phosphomonoesterase activity with aryl phosphate substrates including nicotinamide mononucleotide (NMN), tyrosine phosphate, phenyl phosphate, p-nitrophenyl phosphate, and 4-methylumbelliferyl phosphate. The role of P4 in NAD+ uptake appears to be the dephosphorylation of NMN to nicotinamide riboside, which is then taken up by the organism. Elizabethkingia meningosepticum OlpA is a broad-spectrum nucleotidase with preference for 5'-nucleotides, it efficiently hydrolyzes nucleotide monophosphates, with a strong preference for 5'-nucleotides and for 3'-AMP; OlpA can also hydrolyze sugar phosphates and beta-glycerol phosphate, although with a lower efficiency. Helicobacter pylori HppA is also a 5' nucleotidase. Members of this family belong 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. |
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