Genetic analysis of glucosidase II beta-subunit in trimming of high-mannose-type glycans.
Glucosidase II (G-II) is a glycoprotein-processing enzyme that successively cleaves two alpha1,3-linked glucose residues from N-linked oligosaccharides in the endoplasmic reticulum. G-II is a heterodimer whose alpha-subunit contains a glycosidase active site, but the function(s) of the beta-subunit remain poorly defined. We report here an in vivo enzymatic analysis using gene disruptants lacking either the G-II alpha- or beta-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 beta-subunit retained hydrolytic activity toward p-nitrophenyl alpha-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 beta-subunit was added to the one including the alpha-subunit, the glucosidase activity was restored. These results suggested that the beta-subunit confers the substrate specificity toward di- and monoglucosylated glycans on the glucose-trimming activity of the alpha-subunit.
Watanabe
Taisuke
T
RIKEN Advanced Science Institute, Wako, Saitama, Japan. atwata@riken.jp
Totani
Kiichiro
K
Matsuo
Ichiro
I
Maruyama
Jun-ichi
J
Kitamoto
Katsuhiko
K
Ito
Yukishige
Y
D001236:Aspergillus oryzae / Q000201:enzymology*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005959:Glucosidases / Q000235:genetics / Q000378:metabolism*; D007425:Intracellular Membranes / Q000201:enzymology; D008358:Mannose / Q000378:metabolism; D009844:Oligosaccharides / Q000378:metabolism*; D011134:Polysaccharides / Q000378:metabolism*; D055503:Protein Multimerization; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
D005656:Fungal Proteins; D009844:Oligosaccharides; D011134:Polysaccharides; D021122:Protein Subunits; D005959:Glucosidases; D008358:Mannose