Enhanced Catalysis of Ribonuclease B Folding by the Interaction of Calnexin or Calreticulin with ERp57*
- André Zapun‡§¶,
- Nigel J. Darby‖,
- Daniel C. Tessier‡,
- Marek Michalak**,
- John J. M. Bergeron§ and
- David Y. Thomas‡§‡
- From the ‡Genetics Group, Biotechnology Research Institute, National Research Council of Canada, Montreal, Quebec H4P 2R2, Canada, the §Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 2B2, Canada, the‖European Molecular Biology Laboratory, D-69012 Heidelberg, Germany, the **Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S2, Canada, and the‡Department of Biology, McGill University, Montreal, Quebec H3A 2B2, Canada
Abstract
The endoplasmic reticulum is the site of folding, disulfide bond formation, and N-glycosylation of secretory proteins. Correctly folded proteins are exported from the endoplasmic reticulum, whereas incorrectly folded proteins are retained by a quality control system. The type I membrane-protein calnexin and its soluble homologue calreticulin are constituents of this system that recognize monoglucosylated N-linked glycans that are present on unfolded glycoproteins. Although several components of the quality control apparatus are well characterized, it is not known whether and how they interact with enzymes that catalyze protein folding. The endoplasmic reticulum protein ERp57 is homologous to protein-disulfide isomerase and can be cross-linked to the same monoglucosylated glycoproteins that bind to calnexin and calreticulin. The present study demonstrates that the disulfide isomerase activity of ERp57 on the refolding of monoglucosylated ribonuclease B is much greater when this glycoprotein is associated with calnexin or calreticulin. This result is in contrast to protein-disulfide isomerase, whose activity on monoglucosylated ribonuclease B is decreased in the presence of these lectins. No direct binding of monoglucosylated ribonuclease B or monoglucosylated glycans to ERp57 could be detected, but we show that ERp57 interacts directly with calnexin.
Footnotes
-
↵* This work was supported by grants from the Medical Research Council of Canada (to J. J. M. B. and D. Y. T.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵¶ Medical Research Council of Canada post-doctoral fellow. To whom correspondence should be addressed: Genetics Group, Biotechnology Research Institute NRC, 6100 Royalmount Ave., Montreal, PQ H4P 2R2, Canada. Tel.: 514-496-6156; Fax: 514-496-6213; E-mail: dave.thomas{at}bri.nrc.ca.
-
↵1 The abbreviations used are: ER, endoplasmic reticulum; PDI, protein-disulfide isomerase; RNase B, ribonuclease B; G1, monoglucosylated; UGGT, UDP-glucose:glycoprotein glucosyltransferase; ΔTMC, lumenal domain of canine calnexin; CB, Coomassie Blue; AR, autoradiography; PAGE, polyacrylamide gel electrophoresis; Endo H, endo-β-N-acetylglucosaminidase H.
-
↵2 D. C. Tessier, A. Zapun, N. J. Darby, M. Michalak, J. J. M. Bergeron, and D. Y. Thomas, unpublished data.
-
- Received November 26, 1997.
- Revision received January 8, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
