Genetic analysis of glucosidase II β-subunit in trimming of high-mannose-type glycans

Abstract

Glucosidase II (G-II) is a glycoprotein-processing enzyme that successively cleaves two 1,3-linked glucose residues from N-linked oligosaccharides in the endoplasmic reticulum. G-II is a heterodimer whose -subunit contains a glycosidase active site, but the function(s) of the -subunit remain poorly defined. We report here an in vivo enzymatic analysis using gene disruptants lacking either the G-II or -subunit in the filamentous fungus Aspergillus oryzae. Using synthetic oligosaccharides as probes, G-II activity of the membranous fraction of the gene disruptants was investigated. The fraction lacking the -subunit retained hydrolytic activity toward pnitrophenyl -D-glucopyranoside but was inactive toward both Glc 2 Man 9 GlcNAc 2 and Glc 1 Man 9 GlcNAc 2 . When the fraction containing the -subunit was added to the one including the -subunit, the glucosidase activity was restored. These results suggested that the -subunit confers the substrate specificity toward di-and monoglucosylated glycans on the glucose-trimming activity of the -subunit.