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Glycobiology Advance Access published online on April 24, 2009
Glycobiology, doi:10.1093/glycob/cwp061
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

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

Taisuke Watanabe1,*, Kiichiro Totani1,2, Ichiro Matsuo1,3, Jun-ichi Maruyama4, Katsuhiko Kitamoto4 and Yukishige Ito1,*

1 RIKEN (The Institute of Physical and Chemical Research) Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
4 Department of Biotechnology, The University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan

* Corresponding authors. Tel: +81 48 467 9430; Fax: +81 48 467 4680; E-mail: yukito{at}riken.jp (Y. Ito).

Received on September 29, 2008; accepted on April 18, 2009

Glucosidase II (G-II) is a glycoprotein-processing enzyme that successively cleaves two {alpha}1,3-linked glucose residues from N-linked oligosaccharides in the endoplasmic reticulum (ER). G-II is a heterodimer whose {alpha}-subunit contains a glycosidase active site, but the function(s) of the β-subunit remain poorly defined. We report here an in vivo enzymatic analysis using gene disruptants lacking either the G-II {alpha} or β-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 β-subunit retained hydrolytic activity toward p-nitrophenyl {alpha}-D-glucopyranoside, but was inactive toward both Glc2Man9GlcNAc2 and Glc1Man9GlcNAc2. When the faction containing the β-subunit was added to the one including the {alpha}-subunit, the glucosidase activity was restored. These results suggested that the β-subunit confers the substrate specificity towards di- and monoglucosylated glycans on the glucose-trimming activity of the {alpha}-subunit.

Key words: glucosidase II / glycoprotein / oligosaccharide / quality control / Aspergillus oryzae

2 Current address: Department of Materials and Life Science, Seikei University, Musahino, Tokyo 180-8633 Japan

3 Current address: Department of Chemistry and Chemical Biology, Gunma University, Kiryu 1376-8515 Japan


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