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Glycobiology Advance Access originally published online on June 19, 2009
Glycobiology 2009 19(12):1408-1416; doi:10.1093/glycob/cwp087
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

A novel role for Gtb1p in glucose trimming of N-linked glycans

Robert P Quinn, Sarah J Mahoney, Barrie M Wilkinson, David J Thornton and Colin J Stirling1

Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, UK

1 To whom correspondence should be addressed: Tel: +44-161-275-5104; Fax: +44-161-275-5082; e-mail: colin.stirling{at}manchester.ac.uk

Received on February 10, 2009; revised on June 12, 2009; accepted on June 13, 2009

Glucosidase II (GluII) is a glycan-trimming enzyme active on nascent glycoproteins in the endoplasmic reticulum (ER). It trims the middle and innermost glucose residues (Glc2 and Glc1) from N-linked glycans. The monoglucosylated glycan produced by the first GluII trimming reaction is recognized by calnexin/calreticulin and serves as the signal for entry into this folding pathway. GluII is a heterodimer of {alpha} and β subunits corresponding to yeast Gls2p and Gtb1p, respectively. While Gls2p contains the glucosyl hydrolase active site, the Gtb1p subunit has previously been shown to be essential for the Glc1 trimming event. Here we demonstrate that Gtb1p also determines the rate of Glc2 trimming. In order to further dissect these activities we mutagenized a number of conserved residues across the protein. Our data demonstrate that both the MRH and G2B domains of Gtb1p contribute to the Glc2 trimming event but that the MRH domain is essential for Glc1 trimming.

Key words: calnexin cycle / endoplasmic reticulum / ER quality control / glucosidase II / glycan processing


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