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J. Biol. Chem., Vol. 278, Issue 35, 33078-33087, August 29, 2003

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New Findings on Interactions among the Yeast Oligosaccharyl Transferase Subunits Using a Chemical Cross-linker^*

Aixin Yan, Eilaf Ahmed, Qi Yan  and William J. Lennarz 

From the Department of Biochemistry and Cell Biology and the Institute for Cell and Developmental Biology, State University of New York at Stony Brook, New York 11794-5215

At present, there is very limited knowledge about the structural organization of the yeast oligosaccharyl transferase (OT) complex and the function of each of its nine subunits. Because of the failure of the yeast two-hybrid system to reveal interactions between luminal domains of these subunits, we utilized a membrane permeable, thiocleavable cross-linking reagent dithiobis-succinimidyl propionate to biochemically study the interactions of various OT subunits. Four essential gene products, Ost1p, Wbp1p, Swp1p, and Stt3p were shown to be cross-linked to each other in a pairwise fashion. In addition, Ost1p was found to be cross-linked to all other eight OT subunits individually. This led us to propose that Ost1p may reside in the core of the OT complex and could play an important role in its assembly. Ost4p and Ost5p were found to only interact with specific components of the OT complex and may function as an additional anchor for optimal stability of Stt3p and Ost1p in the membrane, respectively. Interestingly, Ost3p and Ost6p subunits exhibited a surprisingly identical pattern of cross-linking to other subunits, which is consistent with their proposed redundant function. Based on these findings, we analyzed the distribution of the lysine residues that are likely to be involved in cross-linking of OT subunits and propose that the OT subunits interact with each other through either their transmembrane domains and/or a region proximal to it, rather than through their luminal or cytoplasmic domains.

Received for publication, May 21, 2003 , and in revised form, June 12, 2003.

^* This study 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.

Present address: Dept. of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037.

To whom correspondence should be addressed. Tel.: 631-632-8560; Fax: 631-632-8575; E-mail: wlennarz{at}notes.cc.sunysb.edu.

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