A close-up view of oligosaccharyltransferase Many secretory and membrane proteins are modified through the attachment of sugar chains by N-glycosylation. Such modification is required for correct protein folding, targeting, and functionality. In mammalian cells, N-glycosylation is catalyzed by the oligosaccharyltransferase (OST) complex via its STT3 subunit. OST forms a complex with the ribosome and the Sec61 protein translocation channel. Braunger et al. combined cryo–electron microscopy approaches to visualize mammalian ribosome-Sec61-OST complexes in order to build an initial molecular model for mammalian OST. Science, this issue p. 215 Cryo–electron microscopy reveals how cotranslational protein transport and N-glycosylation are coupled in mammals. Protein synthesis, transport, and N-glycosylation are coupled at the mammalian endoplasmic reticulum by complex formation of a ribosome, the Sec61 protein-conducting channel, and oligosaccharyltransferase (OST). Here we used different cryo–electron microscopy approaches to determine structures of native and solubilized ribosome-Sec61-OST complexes. A molecular model for the catalytic OST subunit STT3A (staurosporine and temperature sensitive 3A) revealed how it is integrated into the OST and how STT3-paralog specificity for translocon-associated OST is achieved. The OST subunit DC2 was placed at the interface between Sec61 and STT3A, where it acts as a versatile module for recruitment of STT3A-containing OST to the ribosome-Sec61 complex. This detailed structural view on the molecular architecture of the cotranslational machinery for N-glycosylation provides the basis for a mechanistic understanding of glycoprotein biogenesis at the endoplasmic reticulum.

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哺乳动物内质网偶联蛋白转运和 N-糖基化的结构基础

寡糖基转移酶的特写视图 许多分泌蛋白和膜蛋白通过 N-糖基化连接糖链进行修饰。这种修饰是正确的蛋白质折叠、靶向和功能所必需的。在哺乳动物细胞中，N-糖基化由寡糖基转移酶 (OST) 复合物通过其 STT3 亚基催化。OST 与核糖体和 Sec61 蛋白易位通道形成复合物。布朗格等人。结合冷冻电子显微镜方法来可视化哺乳动物核糖体-Sec61-OST 复合物，以建立哺乳动物 OST 的初始分子模型。科学，这个问题 p。215 冷冻电子显微镜揭示了共翻译蛋白转运和 N-糖基化在哺乳动物中是如何耦合的。蛋白质合成、运输、和 N-糖基化通过核糖体、Sec61 蛋白传导通道和寡糖基转移酶 (OST) 的复杂形成在哺乳动物内质网偶联。在这里，我们使用不同的冷冻电子显微镜方法来确定天然和溶解的核糖体-Sec61-OST 复合物的结构。催化 OST 亚基 STT3A（星形孢菌素和温度敏感 3A）的分子模型揭示了它是如何整合到 OST 中的，以及如何实现对易位子相关 OST 的 STT3 旁系同源特异性。OST 亚基 DC2 被放置在 Sec61 和 STT3A 之间的界面，在那里它作为一个多功能模块，用于将含有 STT3A 的 OST 募集到核糖体-Sec61 复合物。