Structure and 3D Arrangement of Endoplasmic Reticulum Membrane-Associated Ribosomes
Structure and 3D Arrangement of Endoplasmic Reticulum Membrane-Associated Ribosomes
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DOI：
10.1016/j.str.2012.06.010
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发表时间：
2012-09-05
期刊：
影响因子：
5.7
通讯作者：
Foerster, Friedrich
中科院分区：
文献类型：
--
作者：
Pfeffer, Stefan;Brandt, Florian;Foerster, Friedrich
在真核细胞中，共翻译蛋白跨内质网（ER）膜转运需要一个复杂的大分子机制。虽然近年来已经阐明了与纯化和溶解的易位子成分结合的核糖体的结构细节，但在天然膜环境中与完整的ER蛋白易位机制结合的核糖体的结构知识很少。在这里，我们使用冷冻电子断层扫描提供了一个三维重建的80 S核糖体连接到功能犬胰腺ER微粒体原位。在平均分辨率为31埃的亚断层图像中，我们观察到核糖体扩展片段ES27 L和膜的直接接触，并区分了几种膜包埋和内腔复合物，包括Sec61，TRAP复合物和另一种突出90埃进入内腔的大复合物。膜相关核糖体采用优选的三维排列，这可能是ER相关多聚核糖体的特异性，并且可以解释ER相关核糖体与其胞质对应物相比的高翻译效率。
In eukaryotic cells, cotranslational protein translocation across the endoplasmic reticulum (ER) membrane requires an elaborate macromolecular machinery. While structural details of ribosomes bound to purified and solubilized constituents of the translocon have been elucidated in recent years, little structural knowledge of ribosomes bound to the complete ER protein translocation machinery in a native membrane environment exists. Here, we used cryoelectron tomography to provide a three-dimensional reconstruction of 80S ribosomes attached to functional canine pancreatic ER microsomes in situ. In the resulting subtomogram average at 31 angstrom resolution, we observe direct contact of ribosomal expansion segment ES27L and the membrane and distinguish several membrane-embedded and lumenal complexes, including Sec61, the TRAP complex and another large complex protruding 90 angstrom into the lumen. Membrane-associated ribosomes adopt a preferred three-dimensional arrangement that is likely specific for ER-associated polyribosomes and may explain the high translation efficiency of ER-associated ribosomes compared to their cytosolic counterparts.