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J. Biol. Chem., Vol. 280, Issue 24, 22917-22924, June 17, 2005

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Subunits of the Translocon Interact with Components of the Oligosaccharyl Transferase Complex^*

Manasi Chavan, Aixin Yan, and William J. Lennarz

From the Department of Biochemistry and Cell Biology and Institute for Cell and Developmental Biology, Stony Brook University, Stony Brook, New York 11794

Following initiation of translocation across the membrane of the endoplasmic reticulum via the translocon, polypeptide chains are N-glycosylated by the oligosaccharyl transferase (OT) enzyme complex. Translocation and N-glycosylation are concurrent events and would be expected to require juxtaposition of the translocon and the OT complex. To determine whether any of the subunits of the OT complex and translocon mediate interactions between the two complexes, we initiated a systematic study in budding yeast using the split-ubiquitin approach. Interestingly, the OT subunit Stt3p was found to interact only with Sec61p, whereas another OT subunit, Ost4p, was found to interact with all three components of the translocon, Sec61p, Sbh1p, and Sss1p. The OT subunit Wbp1p was found to interact very strongly with Sec61p and Sbh1p and weakly with Sss1p. Other OT subunits, Ost1p, Ost2p, and Swp1p were found to interact with Sec61p and either Sbh1p or Sss1p. Ost3p exhibited a weak interaction with Sec61p and Sbh1p, whereas Ost5p and Ost6p interacted very weakly with Sec61p and failed to interact with Sbh1p or Sss1p. We were able to confirm these split-ubiquitin findings by a chemical cross-linking technique. Based on our findings using these two techniques, we conclude that the association of these two complexes is stabilized via multiple protein-protein contacts. Based on extrapolation of the structural parameters of the crystal structure of the prokaryotic Sec complex to the eukaryotic complex, we propose a working model to understand the organization of the translocon-OT supercomplex.

Received for publication, March 15, 2005 , and in revised form, April 14, 2005.

^* This work was supported by National Institutes of Health Grant GM33185 (to W. J. L.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Dept. of Biochemistry and Cell Biology and Institute for Cell and Developmental Biology, Stony Brook University, Stony Brook, NY 11794. Tel.: 631-632-8560; Fax: 631-632-8575; E-mail: wlennarz{at}notes.cc.sunysb.edu.

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