Serdiuk Tetiana, Balasubramaniam Dhandayuthapani, Sugihara Junichi, Mari Stefania A, Kaback H Ronald, Müller Daniel J
Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule (ETH) Zurich, Basel, Switzerland.
Department of Physiology, University of California-Los Angeles, Los Angeles, California, USA.
Nat Chem Biol. 2016 Nov;12(11):911-917. doi: 10.1038/nchembio.2169. Epub 2016 Sep 5.
How chaperones, insertases and translocases facilitate insertion and folding of complex cytoplasmic proteins into cellular membranes is not fully understood. Here we utilize single-molecule force spectroscopy to observe YidC, a transmembrane chaperone and insertase, sculpting the folding trajectory of the polytopic α-helical membrane protein lactose permease (LacY). In the absence of YidC, unfolded LacY inserts individual structural segments into the membrane; however, misfolding dominates the process so that folding cannot be completed. YidC prevents LacY from misfolding by stabilizing the unfolded state from which LacY inserts structural segments stepwise into the membrane until folding is completed. During stepwise insertion, YidC and the membrane together stabilize the transient folds. Remarkably, the order of insertion of structural segments is stochastic, indicating that LacY can fold along variable pathways toward the native structure. Since YidC is essential in membrane protein biogenesis and LacY is a model for the major facilitator superfamily, our observations have general relevance.
伴侣蛋白、插入酶和转位酶如何促进复杂的细胞质蛋白插入细胞膜并折叠，目前尚未完全了解。在这里，我们利用单分子力谱来观察YidC，一种跨膜伴侣蛋白和插入酶，塑造多跨膜α-螺旋膜蛋白乳糖通透酶（LacY）的折叠轨迹。在没有YidC的情况下，未折叠的LacY将单个结构片段插入膜中；然而，错误折叠在这个过程中占主导地位，以至于折叠无法完成。YidC通过稳定未折叠状态来防止LacY错误折叠，LacY从未折叠状态逐步将结构片段插入膜中，直到折叠完成。在逐步插入过程中，YidC和膜共同稳定瞬时折叠。值得注意的是，结构片段的插入顺序是随机的，这表明LacY可以沿着可变的途径折叠成天然结构。由于YidC在膜蛋白生物合成中至关重要，而LacY是主要促进剂超家族的一个模型，我们的观察结果具有普遍意义。
