Yan Aixin, Lennarz William J
Department of Biochemistry and Cell Biology and the Institute for Cell and Developmental Biology, State University of New York, Stony Brook, NY 11794-5215, USA.
Glycobiology. 2005 Dec;15(12):1407-15. doi: 10.1093/glycob/cwj026. Epub 2005 Aug 11.
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.
寡糖基转移酶（OT）在内质网（ER）中扫描并选择性地将新生多肽链中的 -Asn-X-Thr/Ser- 基序进行糖基化。几个研究小组报道了该酶复合物组成的不同结果。在本研究中，我们使用膜蛋白双杂交方法——分裂泛素系统，发现在酿酒酵母中，除了Ost3p和Ost6p外，OT的所有其他亚基均以二聚体或寡聚体形式存在。在一系列遗传和生化分析中，Ost3p和Ost6p表现出惊人的相似性，但显然不存在于同一个OT复合物中。这一观察结果，以及在一项伴随研究中使用一系列野生型和突变酵母菌株通过蓝色非变性凝胶电泳分析OT复合物组成的结果，有力地表明ER中存在两种OT复合物同工型，仅在是否存在Ost3p或Ost6p方面有所不同。这两种OT复合物同工型各自特异性地与两种结构相似但功能不同的转运体复合物相互作用：Sec61和Ssh1转运体复合物。
