Gene Center Munich and Center for Integrated Protein Science, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany.
Science. 2009 Dec 4;326(5958):1369-73. doi: 10.1126/science.1178535. Epub 2009 Oct 29.
The trimeric Sec61/SecY complex is a protein-conducting channel (PCC) for secretory and membrane proteins. Although Sec complexes can form oligomers, it has been suggested that a single copy may serve as an active PCC. We determined subnanometer-resolution cryo-electron microscopy structures of eukaryotic ribosome-Sec61 complexes. In combination with biochemical data, we found that in both idle and active states, the Sec complex is not oligomeric and interacts mainly via two cytoplasmic loops with the universal ribosomal adaptor site. In the active state, the ribosomal tunnel and a central pore of the monomeric PCC were occupied by the nascent chain, contacting loop 6 of the Sec complex. This provides a structural basis for the activity of a solitary Sec complex in cotranslational protein translocation.
三聚体 Sec61/SecY 复合物是一种用于分泌蛋白和膜蛋白的蛋白传导通道 (PCC)。尽管 Sec 复合物可以形成寡聚体，但有人提出单个拷贝可能作为活性 PCC。我们确定了真核核糖体-Sec61 复合物的亚纳米分辨率冷冻电子显微镜结构。结合生化数据，我们发现，在空闲和活跃状态下，Sec 复合物不是寡聚体，主要通过两个细胞质环与通用核糖体衔接子位点相互作用。在活跃状态下，核糖体隧道和单体 PCC 的中央孔被新生链占据，与 Sec 复合物的环 6 接触。这为翻译共转移中单个 Sec 复合物的活性提供了结构基础。
