N-terminal catalytic domain of mainly uncharacterized eukaryotic proteins similar to alpha-mannosidases; glycoside hydrolase family 38 (GH38). The subfamily of mainly uncharacterized eukaryotic proteins shows sequence homology with class II alpha-mannosidases (AlphaAMIIs). AlphaAMIIs possess a-1,3, a-1,6, and a-1,2 hydrolytic activity, and catalyze the degradation of N-linked oligosaccharides. The N-terminal catalytic domain of alphaMII adopts a structure consisting of parallel 7-stranded beta/alpha barrel. This subfamily belongs to the GH38 family of retaining glycosyl hydrolases, which employ a two-step mechanism involving the formation of a covalent glycosyl enzyme complex; two carboxylic acids positioned within the active site act in concert: one as a catalytic nucleophile and the other as a general acid/base catalyst.
N-terminal catalytic domain of class II alpha-mannosidases and similar proteins; glycoside hydrolase family 38 (GH38). Alpha-mannosidases (EC 3.2.1.24) are extensively found in eukaryotes and play important roles in the processing of newly formed N-glycans and in degradation of mature glycoproteins. A deficiency of this enzyme causes the lysosomal storage disease alpha-mannosidosis. Many bacterial and archaeal species also possess putative alpha-mannosidases, but their activity and specificity is largely unknown. Based on different functional characteristics and sequence homology, alpha-mannosidases have been organized into two classes (class I, belonging to glycoside hydrolase family 47, and class II, belonging to glycoside hydrolase family 38). Members of this family corresponds to class II alpha-mannosidases (alphaMII), which contain intermediate Golgi alpha-mannosidases II, acidic lysosomal alpha-mannosidases, animal sperm and epididymal alpha -mannosidases, neutral ER/cytosolic alpha-mannosidases, and some putative prokaryotic alpha-mannosidases. AlphaMII possess a-1,3, a-1,6, and a-1,2 hydrolytic activity, and catalyzes the degradation of N-linked oligosaccharides. The N-terminal catalytic domain of alphaMII adopts a structure consisting of parallel 7-stranded beta/alpha barrel. Members in this family are retaining glycosyl hydrolases of family GH38 that employs a two-step mechanism involving the formation of a covalent glycosyl enzyme complex. Two carboxylic acids positioned within the active site act in concert: one as a catalytic nucleophile and the other as a general acid/base catalyst.
N-terminal catalytic domain of eukaryotic class II alpha-mannosidases; glycoside hydrolase family 38 (GH38). The family corresponds to a group of eukaryotic class II alpha-mannosidases (AlphaMII), which contain Golgi alpha-mannosidases II (GMII), the major broad specificity lysosomal alpha-mannosidases (LAM, MAN2B1), the noval core-specific lysosomal alpha 1,6-mannosidases (Epman, MAN2B2), and similar proteins. GMII catalyzes the hydrolysis of the terminal both alpha-1,3-linked and alpha-1,6-linked mannoses from the high-mannose oligosaccharide GlcNAc(Man)5(GlcNAc)2 to yield GlcNAc(Man)3(GlcNAc)2 (GlcNAc, N-acetylglucosmine), which is the committed step of complex N-glycan synthesis. LAM is a broad specificity exoglycosidase hydrolyzing all known alpha 1,2-, alpha 1,3-, and alpha 1,6-mannosidic linkages from numerous high mannose type oligosaccharides. Different from LAM, Epman 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. Members in this family are retaining glycosyl hydrolases of family GH38 that employs a two-step mechanism involving the formation of a covalent glycosyl enzyme complex. Two carboxylic acids positioned within the active site act in concert: one as a catalytic nucleophile and the other as a general acid/base catalyst.