Eaglesfield Ross, Madsen Mary Ann, Sanyal Suparna, Reboud Julien, Amtmann Anna
Institute of Molecular, Cell and Systems Biology, University of Glasgow College of Medical, Veterinary and Life Sciences, Glasgow G12 8QQ, UK.
Division of Biomedical Engineering, University of Glasgow School of Engineering, Glasgow G12 8QQ, UK.
iScience. 2021 Apr 20;24(5):102429. doi: 10.1016/j.isci.2021.102429. eCollection 2021 May 21.
The emergence of lipid membranes and embedded proteins was essential for the evolution of cells. Translocon complexes mediate cotranslational recruitment and membrane insertion of nascent proteins, but they already contain membrane-integral proteins. Therefore, a simpler mechanism must exist, enabling spontaneous membrane integration while preventing aggregation of unchaperoned protein in the aqueous phase. Here, we used giant unilamellar vesicles encapsulating minimal translation components to systematically interrogate the requirements for insertion of the model protein proteorhodopsin (PR) - a structurally ubiquitous membrane protein. We show that the N-terminal hydrophobic domain of PR is both necessary and sufficient for cotranslational recruitment of ribosomes to the membrane and subsequent membrane insertion of PR. Insertion of N-terminally truncated PR was restored by artificially attaching ribosomes to the membrane. Our findings offer a self-sufficient protein-inherent mechanism as a possible explanation for effective membrane protein biogenesis in a "pretranslocon" era, and they offer new opportunities for generating artificial cells.
脂膜和嵌入蛋白的出现对细胞进化至关重要。转位子复合物介导新生蛋白的共翻译招募和膜插入，但它们已经包含膜整合蛋白。因此，必然存在一种更简单的机制，既能实现自发的膜整合，又能防止未受伴侣蛋白保护的蛋白在水相中聚集。在这里，我们使用包裹最小翻译组件的巨型单层囊泡，系统地探究了模型蛋白视紫质（PR）——一种结构上普遍存在的膜蛋白插入的要求。我们表明，PR的N端疏水结构域对于核糖体向膜的共翻译招募以及随后PR的膜插入既必要又充分。通过人工将核糖体附着于膜上，可恢复N端截短的PR的插入。我们的发现提供了一种自给自足的蛋白质固有机制，作为对“前转位子”时代有效膜蛋白生物合成的一种可能解释，并且为生成人工细胞提供了新机会。
