Komar Joanna, Alvira Sara, Schulze Ryan J, Martin Remy, Lycklama A Nijeholt Jelger A, Lee Sarah C, Dafforn Tim R, Deckers-Hebestreit Gabriele, Berger Imre, Schaffitzel Christiane, Collinson Ian
School of Biochemistry, University of Bristol, Bristol BS8 1TD, U.K.
European Molecular Biology Laboratory, Grenoble Outstation, 6 rue Jules Horowitz, Grenoble 38042, France.
Biochem J. 2016 Oct 1;473(19):3341-54. doi: 10.1042/BCJ20160545. Epub 2016 Jul 19.
Protein secretion and membrane insertion occur through the ubiquitous Sec machinery. In this system, insertion involves the targeting of translating ribosomes via the signal recognition particle and its cognate receptor to the SecY (bacteria and archaea)/Sec61 (eukaryotes) translocon. A common mechanism then guides nascent transmembrane helices (TMHs) through the Sec complex, mediated by associated membrane insertion factors. In bacteria, the membrane protein 'insertase' YidC ushers TMHs through a lateral gate of SecY to the bilayer. YidC is also thought to incorporate proteins into the membrane independently of SecYEG. Here, we show the bacterial holo-translocon (HTL) - a supercomplex of SecYEG-SecDF-YajC-YidC - is a bona fide resident of the Escherichia coli inner membrane. Moreover, when compared with SecYEG and YidC alone, the HTL is more effective at the insertion and assembly of a wide range of membrane protein substrates, including those hitherto thought to require only YidC.
蛋白质分泌和膜插入通过普遍存在的Sec机制发生。在这个系统中，插入涉及通过信号识别颗粒及其同源受体将正在翻译的核糖体靶向到SecY（细菌和古细菌）/Sec61（真核生物）转运体。然后，一种共同机制在相关膜插入因子的介导下，引导新生跨膜螺旋（TMH）穿过Sec复合物。在细菌中，膜蛋白“插入酶”YidC通过SecY的侧向门将TMH引导至双层膜。YidC也被认为可以独立于SecYEG将蛋白质整合到膜中。在这里，我们展示了细菌全转运体（HTL）——一种SecYEG-SecDF-YajC-YidC的超复合物——是大肠杆菌内膜的真正驻留物。此外，与单独的SecYEG和YidC相比，HTL在多种膜蛋白底物的插入和组装方面更有效，包括那些迄今被认为仅需要YidC的底物。
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