Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, 020-8550 Iwate, Japan.
Proc Natl Acad Sci U S A. 2013 Jun 11;110(24):9734-9. doi: 10.1073/pnas.1303160110. Epub 2013 May 28.
Presecretory proteins are translocated across biological membranes through protein-conducting channels such as Sec61 (eukaryotes) and SecYEG (bacteria). SecA, a translocation ATPase, pushes preproteins out with dynamic structural changes through SecYEG. SecG, a subunit of the SecYEG channel possessing two transmembrane stretches (TMs), undergoes topology inversion coupled with SecA-dependent translocation. Recently, we characterized membrane protein integrase (MPIase), a glycolipozyme involved in not only protein integration into membranes but also preprotein translocation. We report here that SecG inversion occurs only when MPIase associates with SecYEG. We also found that MPIase modulates the dimer orientation of SecYEG. Cysteine-scanning mutagenesis mapped SecG TM 2 to a relatively hydrophilic environment. The dimer formation of SecG, crosslinked at TM 2, was not observed on SecG inversion, indicating that SecYEG undergoes a dynamic structural change during preprotein translocation.
前体蛋白通过蛋白传导通道（如 Sec61（真核生物）和 SecYEG（细菌））跨生物膜易位。SecA 是一种易位 ATP 酶，通过 SecYEG 以动态结构变化推动前体蛋白。SecG 是 SecYEG 通道的一个亚基，具有两个跨膜区（TMs），与 SecA 依赖性易位偶联进行拓扑倒置。最近，我们对参与蛋白质整合到膜中以及前体蛋白易位的糖脂酶膜蛋白整合酶（MPIase）进行了表征。我们在这里报告说，只有当 MPIase 与 SecYEG 结合时，SecG 才会发生倒置。我们还发现 MPIase 调节 SecYEG 的二聚体取向。半胱氨酸扫描突变将 SecG TM 2 映射到相对亲水的环境中。在 SecG 倒置时未观察到 SecG TM 2 交联的 SecG 二聚体形成，表明在前体蛋白易位过程中 SecYEG 发生动态结构变化。
