Department of Biochemistry and Molecular Biology and the Center for Membrane Biology, University of Texas McGovern Medical School at Houston, Houston, TX, 77030, USA.
Sci Rep. 2019 Aug 5;9(1):11338. doi: 10.1038/s41598-019-47824-y.
Membrane proteins play key roles in cellular functions, their activity mainly depending on their topological arrangement in membranes. Structural studies of membrane proteins have long adopted a protein-centric view regarding the determinants of membrane protein topology and function. Several studies have shown that the orientation of transmembrane domains of polytopic membrane proteins with respect to the plane of the lipid bilayer can be largely determined by membrane lipid composition. However, the mechanism by which membrane proteins exhibit structural and functional duality in the same membrane or different membranes is still unknown. Here we show that lipid-dependent structural and functional assessment of a membrane protein can be conducted in detergent micelles, opening the possibility for the determination of lipid-dependent high-resolution crystal structures. We found that the lactose permease purified from Escherichia coli cells exhibiting varied phospholipid compositions exhibits the same topology and similar function as in its membrane of origin. Furthermore, we found several conditions, including protein mutations and micelle lipid composition, that lead to increased protein stability, correlating with a higher yield of two-dimensional crystal formation. Altogether, our results demonstrate how the membrane lipid environment influences membrane protein topology and arrangement, both in native membranes and in mixed detergent micelles.
膜蛋白在细胞功能中发挥着关键作用，其活性主要取决于它们在膜中的拓扑排列。长期以来，膜蛋白的结构研究一直采用以蛋白质为中心的观点来研究膜蛋白拓扑结构和功能的决定因素。有几项研究表明，具有多个跨膜结构域的多价膜蛋白的跨膜结构域相对于脂质双层平面的方向可以在很大程度上由膜脂组成决定。然而，膜蛋白在同一膜或不同膜中表现出结构和功能双重性的机制尚不清楚。在这里，我们表明可以在去污剂胶束中对膜蛋白进行依赖脂质的结构和功能评估，这为确定依赖脂质的高分辨率晶体结构开辟了可能性。我们发现，从具有不同磷脂组成的大肠杆菌细胞中纯化出的乳糖通透酶表现出与原始膜相同的拓扑结构和相似的功能。此外，我们发现了几种条件，包括蛋白质突变和胶束脂质组成，这些条件导致蛋白质稳定性增加，与二维晶体形成的更高产量相关。总之，我们的结果表明膜脂质环境如何影响天然膜和混合去污剂胶束中膜蛋白的拓扑结构和排列。
