phosphomannomutase, similar to human PMM1 and PMM2, Saccharomyces Sec53p, and Arabidopsis thaliana PMM
PMM catalyzes the interconversion of mannose-6-phosphate (M6P) to mannose-1-phosphate (M1P); the conversion of M6P to M1P is an essential step in mannose activation and the biosynthesis of glycoconjugates in all eukaryotes. M1P is the substrate for the synthesis of GDP-mannose, which is an intermediate for protein glycosylation, protein sorting and secretion, and maintaining a functional endomembrane system in eukaryotic cells. Proteins in this family contains a conserved phosphorylated motif DxDx(T/V) shared with some other phosphotransferases. This family contains two human homologs, PMM1 and PMM2; PMM2 deficiency causes congenital disorder of glycosylation type I-a, also known as Jaeken syndrome. PMM1 can also act as glucose-1,6-bisphosphatase in the brain after stimulation with inosine monophosphate; PMM2 on the other hand, is insensitive to IMP and demonstrates low glucose-1,6-bisphosphatase activity. Arabidopsis thaliana PMM converted M1P into M6P and glucose-1-phosphate into glucose-6-phosphate, with the latter reaction being less efficient. Arabidopsis thaliana and Nicotiana benthamian PPMs are involved in ascorbic acid biosynthesis. 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.