Glycobiology Advance Access originally published online on August 11, 2005
Glycobiology 2005 15(12):1407-1415; doi:10.1093/glycob/cwj026
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© Published by Oxford University Press 2005.
Two oligosaccharyl transferase complexes exist in yeast and associate with two different translocons
Department of Biochemistry and Cell Biology and the Institute for Cell and Developmental Biology, State University of New York, Stony Brook, NY 11794-5215
1 To whom correspondence should be addressed; e-mail: wlennarz{at}notes.cc.sunysb.edu
Received on July 5, 2005; revised on August 3, 2005; accepted on August 3, 2005
Oligosaccharyl transferase (OT) scans and selectively glycosylates Asn-X-Thr/Ser-motifs in nascent polypeptide chains in the endoplasmic reticulum (ER). Several groups have reported different results for the composition of this enzyme complex. In this study, using a membrane protein two-hybrid approach, the split-ubiquitin system, we show that except for Ost3p and Ost6p, all of the other subunits of OT exist as dimers or oligomers in the yeast, Saccharomyces cerevisiae. Ost3p and Ost6p behave strikingly similar in a series of genetic and biochemical assays, but clearly do not exist in the same OT complex. This observation, as well as the results in an accompanying study to analyze the composition of OT complex by blue native gel electrophoresis using a series of wild-type and mutant yeast strains strongly suggests that two isoforms of the OT complex exist in the ER, differing only in the presence of Ost3p or Ost6p. Each of these two isoforms of the OT complex specifically interacts with two structurally similar, but functionally different translocon complexes: the Sec61 and the Ssh1 translocon complexes.
Key words: oligosaccharyl transferase / Sec61 translocon / split-ubiquitin system / Ssh1 translocon
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