Fujii Satoshi, Matsuura Tomoaki, Yomo Tetsuya
†Japan Science and Technology (JST), ERATO, Yomo Dynamical Micro-scale Reaction Environment Project, 1-5 Yamadaoka, Suita, Osaka 565-0871, Japan.
‡Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
ACS Chem Biol. 2015 Jul 17;10(7):1694-701. doi: 10.1021/acschembio.5b00107. Epub 2015 Apr 22.
Membrane proteins perform their functions within or on the lipid membrane, and lipid compositions are known to affect membrane protein integration and activity. Recently, the geometric aspect of membrane curvature was shown to play an important role in membrane protein behavior. Certain membrane proteins are known to sense the curvature of the membrane and to preferentially bind to highly curved membranes. However, although numerous membrane proteins assemble to form homo- or heterocomplexes and perform their biological functions, the dependence of membrane protein assembly on membrane curvature remains elusive. In this study, we analyzed the effect of the membrane curvature on the nanopore formation of α-hemolysin (AH), which is a toxic membrane protein derived from Staphylococcus aureus. The AH protein binds to the membrane as a monomer, assembles to form a heptamer, and forms a nanopore. By simultaneously measuring the molecules bound to the membrane and the activities of the nanopore on the membrane, we determined the nanopore formation ratio of AH. We used various sizes of liposomes and analyzed the dependence on the membrane curvature by using flow cytometry. Combining the results for positive and negative curvature, we found that the nanopore formation ratio of AH was curvature sensitive and was higher in a flat membrane than in a curved membrane. Furthermore, the nanopore formation ratio was almost identical or relatively higher in membranes with negative curvature than those with positive curvature.
膜蛋白在脂质膜内或膜上发挥其功能，并且已知脂质组成会影响膜蛋白的整合和活性。最近，膜曲率的几何因素被证明在膜蛋白行为中起重要作用。某些膜蛋白已知能感知膜的曲率，并优先结合高度弯曲的膜。然而，尽管许多膜蛋白组装形成同型或异型复合物并执行其生物学功能，但膜蛋白组装对膜曲率的依赖性仍然不清楚。在本研究中，我们分析了膜曲率对α-溶血素（AH）纳米孔形成的影响，α-溶血素是一种源自金黄色葡萄球菌的有毒膜蛋白。AH蛋白以单体形式结合到膜上，组装形成七聚体，并形成纳米孔。通过同时测量结合到膜上的分子和膜上纳米孔的活性，我们确定了AH的纳米孔形成率。我们使用了各种大小的脂质体，并通过流式细胞术分析了对膜曲率的依赖性。综合正曲率和负曲率的结果，我们发现AH的纳米孔形成率对曲率敏感，在平膜中比在弯曲膜中更高。此外，在具有负曲率的膜中，纳米孔形成率几乎相同或相对高于具有正曲率的膜。
