N-terminal catalytic domain of mammalian core-specific lysosomal alpha 1,6-mannosidase and similar proteins; glycoside hydrolase family 38 (GH38)
The subfamily is represented by a novel human core-specific lysosomal alpha 1,6-mannosidase (Epman, Man2B2) and similar proteins. Although it was previously named as epididymal alpha-mannosidase, Epman has a broadly distributed transcript expression profile. Different from the major broad specificity lysosomal alpha-mannosidases (LAM, MAN2B1), Epman is not associated with genetic alpha-mannosidosis that is caused by the absence of LAM. Furthermore, Epman has unique substrate specificity. It can efficiently cleave only the alpha 1,6-linked mannose residue from (Man)3GlcNAc, but not (Man)3(GlcNAc)2 or other larger high mannose oligosaccharides, in the core of N-linked glycans. In contrast, the major LAM can cleave all of the alpha-linked mannose residues from high mannose oligosaccharides except the core alpha 1,6-linked mannose residue. Moreover, it is suggested that the catalytic activity of Epman is dependent on prior action by di-N-acetyl-chitobiase (chitobiase), which indicates there is a functional cooperation between these two enzymes for the full and efficient catabolism of mammalian lysosomal N-glycan core structures. Epman has an acidic pH optimum. It is strongly stimulated by cobalt or zinc ions and strongly inhibited by furanose analogues swainsonine (SW) and 1,4-dideoxy-1,4-imino-d-mannitol (DIM).
Jiyao W et al.(2023). "The conserved domain database in 2023.",