N-glycosylation is a ubiquitous modification of eukaryotic secretory and membrane-bound proteins; about 90% of glycoproteins are N-glycosylated. The reaction is catalysed by an eight-protein oligosaccharyltransferase (OST) complex that is embedded in the endoplasmic reticulum membrane. Our understanding of eukaryotic protein N-glycosylation has been limited owing to the lack of high-resolution structures. Here we report a 3.5 Å resolution cryo-electron microscopy structure of the Saccharomyces cerevisiae OST complex, revealing the structures of subunits Ost1–Ost5, Stt3, Wbp1 and Swp1. We found that seven phospholipids mediate many of the inter-subunit interactions, and an Stt3 N-glycan mediates interactions with Wbp1 and Swp1 in the lumen. Ost3 was found to mediate the OST–Sec61 translocon interface, funnelling the acceptor peptide towards the OST catalytic site as the nascent peptide emerges from the translocon. The structure provides insights into co-translational protein N-glycosylation, and may facilitate the development of small-molecule inhibitors that target this process.

中文翻译：

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真核寡糖基转移酶复合物的原子结构

N-糖基化是真核分泌蛋白和膜结合蛋白的普遍修饰；大约 90% 的糖蛋白是 N-糖基化的。该反应由嵌入内质网膜的八蛋白寡糖基转移酶 (OST) 复合物催化。由于缺乏高分辨率结构，我们对真核蛋白质 N-糖基化的理解受到限制。在这里，我们报告了酿酒酵母 OST 复合体的 3.5 Å 分辨率冷冻电子显微镜结构，揭示了亚基 Ost1–Ost5、Stt3、Wbp1 和 Swp1 的结构。我们发现七种磷脂介导了许多亚基间相互作用，并且 Stt3 N-聚糖介导了与腔中 Wbp1 和 Swp1 的相互作用。发现 Ost3 介导 OST-Sec61 易位接口，当新生肽从易位子中出现时，将受体肽汇集到 OST 催化位点。该结构提供了对共翻译蛋白 N-糖基化的见解，并可能促进针对该过程的小分子抑制剂的开发。