Structure of the native Sec61 protein-conducting channel.
Structure of the native Sec61 protein-conducting channel.
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DOI：
10.1038/ncomms9403
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发表时间：
2015-09-28
影响因子：
16.6
通讯作者：
Förster F
中科院分区：
文献类型：
--
作者：
Pfeffer S;Burbaum L;Unverdorben P;Pech M;Chen Y;Zimmermann R;Beckmann R;Förster F
在哺乳动物细胞中，分泌蛋白和膜蛋白通过普遍保守的蛋白质传导通道Sec61转运穿过内质网（ER）膜或插入内质网膜。Sec61在分离的、洗涤剂溶解的状态下已进行了结构研究。在此，我们利用冷冻电子断层扫描和核糖体图谱技术，对粗面内质网囊泡上天然的、未溶解的核糖体 - Sec61复合物进行结构和功能表征。令人惊讶的是，9 Å分辨率的子断层平均图显示Sec61处于侧向开放构象，即使该通道并非处于将膜蛋白插入脂质双层的过程中。与近期关于多肽转运和插入的机制模型相反，我们的研究结果表明，Sec61的侧向开放构象是核糖体结合的易位子复合物中唯一存在的构象，与其功能状态无关。与早期的功能研究一致，我们的结构表明，即使没有新生链，仅核糖体在脂质环境中就足以使Sec61侧向开放。
蛋白质传导通道Sec61负责内质网的蛋白质转运和膜插入。在此，作者在天然环境中确定了核糖体结合的Sec61的结构，其中它无论其功能状态如何都采用侧向开放构象。
In mammalian cells, secretory and membrane proteins are translocated across or inserted into the endoplasmic reticulum (ER) membrane by the universally conserved protein-conducting channel Sec61, which has been structurally studied in isolated, detergent-solubilized states. Here we structurally and functionally characterize native, non-solubilized ribosome-Sec61 complexes on rough ER vesicles using cryo-electron tomography and ribosome profiling. Surprisingly, the 9-Å resolution subtomogram average reveals Sec61 in a laterally open conformation, even though the channel is not in the process of inserting membrane proteins into the lipid bilayer. In contrast to recent mechanistic models for polypeptide translocation and insertion, our results indicate that the laterally open conformation of Sec61 is the only conformation present in the ribosome-bound translocon complex, independent of its functional state. Consistent with earlier functional studies, our structure suggests that the ribosome alone, even without a nascent chain, is sufficient for lateral opening of Sec61 in a lipid environment. The protein-conducting channel Sec61 is responsible for protein transport and membrane insertion at the endoplasmic reticulum. Here, the authors determine the structure of ribosome-bound Sec61 in a native context, in which it adopts a laterally open conformation, irrespective of its functional state.