Protein transport via the Sec translocon represents an evolutionary conserved mechanism for delivering cytosolically-synthesized proteins to extra-cytosolic compartments. The Sec translocon has a three-subunit core, termed Sec61 in Eukaryotes and SecYEG in Bacteria. It is located in the endoplasmic reticulum of Eukaryotes and in the cytoplasmic membrane of Bacteria where it constitutes a channel that can be activated by multiple partner proteins. These partner proteins determine the mechanism of polypeptide movement across the channel. During SRP-dependent co-translational targeting, the ribosome threads the nascent protein directly into the Sec channel. This pathway is in Bacteria mainly dedicated for membrane proteins but in Eukaryotes also employed by secretory proteins. The alternative pathway, leading to post-translational translocation across the Sec translocon engages an ATP-dependent pushing mechanism by the motor protein SecA in Bacteria and a ratcheting mechanism by the lumenal chaperone BiP in Eukaryotes. Protein transport and biogenesis is also assisted by additional proteins at the lateral gate of SecY/Sec61α and in the lumen of the endoplasmic reticulum or in the periplasm of bacterial cells. The modular assembly enables the Sec complex to transport a vast array of substrates. In this review we summarize recent biochemical and structural information on the prokaryotic and eukaryotic Sec translocons and we describe the remarkably complex interaction network of the Sec complexes.

经由Sec translocon的蛋白质转运代表了将细胞质合成的蛋白质递送至胞外区室的进化保守机制。Sec转运子具有三个亚基核心，在真核生物中称为Sec61，在细菌中称为SecYEG。它位于真核生物的内质网和细菌的细胞质膜中，在此处构成可以被多种伴侣蛋白激活的通道。这些伴侣蛋白决定了多肽跨通道运动的机制。在依赖SRP的共翻译靶向过程中，核糖体将新生蛋白直接穿入Sec通道。该途径在细菌中主要用于膜蛋白，但在真核生物中也被分泌蛋白利用。替代途径 导致跨Sec转录翻译后易位的过程与细菌中的运动蛋白SecA参与了ATP依赖的推动机制，而在真核生物中由腔内伴侣BiP参与了棘轮机制。SecY /Sec61α的侧门以及内质网腔或细菌细胞周质中的其他蛋白质也有助于蛋白质的运输和生物发生。模块化组件使Sec复合物能够运输大量基板。在这篇综述中，我们总结了有关原核和真核Sec易位子的最新生化和结构信息，并且我们描述了Sec配合物非常复杂的相互作用网络。