Structures of the Sec61 complex engaged in nascent peptide translocation or membrane insertion
Structures of the Sec61 complex engaged in nascent peptide translocation or membrane insertion
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DOI：
10.1038/nature12950
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发表时间：
2014-02-06
期刊：
影响因子：
64.8
通讯作者：
Beckmann, Roland
中科院分区：
文献类型：
--
作者：
Gogala, Marko;Becker, Thomas;Beckmann, Roland
分泌蛋白以及跨膜蛋白的生物发生需要普遍保守的蛋白质传导通道（PCC）即Sec61复合物（细菌中的SecY复合物）的活性（1）。在真核细胞中，PCC位于内质网膜上，在那里它可与正在翻译的核糖体结合，以进行共翻译蛋白质转运。Sec复合物由三个亚基（Sec61α、β和γ）组成，为亲水肽的易位提供了一个水性环境，并且在Sec61α亚基中有一个侧向开口，该开口被认为是疏水域膜分配的一个门（2）。一个塞螺旋和一个所谓的孔环被认为可密封PCC以防止离子流动，并被认为会重新排列以容纳易位肽（2,3）。几个晶体结构和冷冻电镜结构揭示了封闭和部分开放的Sec61和SecY复合物的不同构象（2,4 - 8）。然而，在这些样本中，没有一个在生化上明确界定了易位状态。在此，我们展示了与核糖体结合的Sec61复合物在新生肽易位或膜插入过程中的冷冻电镜结构。我们的数据表明，一个亲水肽可以通过Sec复合物易位，其侧向门基本关闭，中央通道仅稍有重新排列。一个疏水域的膜插入似乎是在Sec复合物打开所提出的侧向门的同时发生的，同时重新排列塞以维持离子渗透屏障。总之，我们为Sec61复合物作为蛋白质传导通道的基本活性提供了一个结构模型。
The biogenesis of secretory as well as transmembrane proteins requires the activity of the universally conserved protein-conducting channel (PCC), the Sec61 complex (SecY complex in bacteria)(1). In eukaryotic cells the PCC is located in the membrane of the endoplasmic reticulum where it can bind to translating ribosomes for co-translational protein transport. The Sec complex consists of three subunits (Sec61 alpha, beta and gamma) and provides an aqueous environment for the translocation of hydrophilic peptides as well as a lateral opening in the Sec61a subunit that has been proposed to act as a gate for the membrane partitioning of hydrophobic domains(2). A plug helix and a so-called pore ring are believed to seal the PCC against ion flow and are proposed to rearrange for accommodation of translocating peptides(2,3). Several crystal and cryo-electron microscopy structures revealed different conformations of closed and partially open Sec61 and SecY complexes(2,4-8). However, in none of these samples has the translocation state been unambiguously defined biochemically. Here we present cryo-electron microscopy structures of ribosome-bound Sec61 complexes engaged in translocation or membrane insertion of nascent peptides. Our data show that a hydrophilic peptide can translocate through the Sec complex with an essentially closed lateral gate and an only slightly rearranged central channel. Membrane insertion of a hydrophobic domain seems to occur with the Sec complex opening the proposed lateral gate while rearranging the plug to maintain an ion permeability barrier. Taken together, we provide a structural model for the basic activities of the Sec61 complex as a protein-conducting channel.