InterPro domain: IPR039794

Glucosidase II catalyses the sequential removal of two alpha-1,3-linked glucose residues in the second step of N-linked oligosaccharide processing. It is a heterodimer whose alpha subunit bears the glycosyl hydrolase active site, while its beta subunit role is controversial. The beta subunit has been reported to be involved in the solubility and stability of the heterodimeric enzyme, and in retaining the enzyme within the endoplasmic reticulum [ 1 ]. Other studies suggest that the beta subunit modulates N-Glycan trimming in both fission yeast and mammals [ 2 , 3 , 4 ].

N-acetylglucosamine-1-phosphotransferase subunit gamma (GNPTG) is a non-catalytic component of the N-acetylglucosamine-1-phosphotransferase complex. The complex is lysoosomal and a heterohexamer consisting of two alpha, two beta and two gamma subunits, and is required for the first step in the synthesis of the mannose 6-phosphate recognition marker on lysosomal acid hydrolases. The gamma subunit facilitates the addition of a second GlcNAc-P to the high mannose oligosaccharides of the substrates [ 5 ]. Mutations in the gene for the gamma subunit are associated with mucolipidosis type III complementation group C (MLIIIC), an autosomal recessive disease of lysosomal hydrolase trafficking [ 6 ].

This entry includes glucosidase II beta subunit from eukaryotes and N-acetylglucosamine-1-phosphotransferase subunit gamma from animals. They share a conserved N-terminal domain.

1. The heterodimeric structure of glucosidase II is required for its activity, solubility, and localization in vivo. Glycobiology 10, 815-27
2. Yeast GTB1 encodes a subunit of glucosidase II required for glycoprotein processing in the endoplasmic reticulum. J. Biol. Chem. 281, 6325-33
3. A novel role for Gtb1p in glucose trimming of N-linked glycans. Glycobiology 19, 1408-16
4. Glucosidase II beta subunit modulates N-glycan trimming in fission yeasts and mammals. Mol. Biol. Cell 20, 3974-84
5. Functions of the alpha, beta, and gamma subunits of UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. J. Biol. Chem. 285, 3360-70
6. Molecular basis of variant pseudo-hurler polydystrophy (mucolipidosis IIIC) J. Clin. Invest. 105, 673-81