Small K+ channels are model proteins for detecting basic interactions between membrane proteins and their surrounding bilayer with relevance for structure and function

膜蛋白的结构/功能相关性只能通过对蛋白质与其脂质环境之间复杂相互作用的深刻了解才能完全理解。在过去的十年里，许多工作致力于了解跨膜结构域（TMD）的基本结构及其嵌入脂质双层。在这方面，用简单合成的单跨膜蛋白的系统研究提供了α-螺旋TMD的氨基酸组成的许多基本规则。本项目的目标是扩展这种系统的方法，并通过进入更高层次的复杂性，其中包括一个可测量的功能，检查膜蛋白的结构/功能相关性。具有不同TMD的小病毒K+通道为这一奋进提供了理想的工具。这些功能性通道蛋白的亚基由两个TMD组成，它们的长度刚好足以跨越一个膜。通过大量的实验和结构工作，我们已经知道这些通道的TMDS的基本特性，这对于蛋白质在膜中的锚定非常重要。该项目的成功实现得到了实验进展的进一步支持，这使我们能够通过在所谓的纳米盘中进行体外翻译来生产通道蛋白。从那里，它们可以在各种类型的脂质双层中重构，并且它们的功能被记录为单通道波动。有了这个坚实的背景下，我们建议系统地研究模型通道蛋白的功能特性与不同的TMD在脂质双层不同的化学风味，如可变双层厚度，不同的头基团和有或没有胆固醇。这项工作将得到补充的结构工作，其中小和广角X-射线散射方法被用来确定的通道蛋白的脂质双层的几何形状的效果。将采用高分辨率显微镜检查不同膜中通道簇的潜在形成。这些互补的实验将为了解可变脂质环境中简单通道蛋白的结构和功能关系提供坚实的数据基础。我们将获得有关不同膜特性对K+通道功能影响的详细信息，包括门控和单位电导。数据将进一步显示两个伴侣，例如膜和蛋白质，如何补偿TMD长度相对于双层厚度的错配而不损害功能。病毒K+通道的一般结构类似于复杂通道的孔结构，这一事实打开了将本研究的数据外推到生理学相关K+通道的可能性。

Structure/function correlates of membrane proteins can only be fully understood with profound knowledge on the complex interplay between proteins with their lipid environment. In the last decade much work was devoted to understand the basic architecture of transmembrane domains (TMDs) and their embedding in lipid bilayers. A systematic research with simple synthetic one membrane spanning proteins has in this context provided many of the basic rules for the amino acid composition of a-helical TMDs. The goal of the present project is to extend this systematic approach and examine structure/function correlates of membrane proteins by entering a higher level of complexity, which includes a measurable function. Ideal tools for this endeavor are provided by small viral K+ channels with different TMDs. A subunit of these functional channel proteins is built from two TMDs, which are just long enough to span a membrane. From a bulk of experimental and structural work we already know essential properties of the TMDS of these channels, which are important for an anchoring of the proteins in the membrane. A successful realization of the project is further supported by experimental progress, which allows us to produce channel proteins by in vitro translation in so called nano-discs. From there they can be reconstituted in various types of lipid bilayers and their function recorded as single channel fluctuations. With this solid background we propose to systematically examine the functional properties of model channel proteins with different TMDs in lipid bilayers with distinct physic chemical flavors like variable bilayer thickness, different head groups and with or without cholesterol. This work will be complemented by structural work in which small and wide angle X-ray scattering methods are used to determine the effect of the channel proteins on the geometry of the lipid bilayer. High-resolution microscopy will be employed to examine the potential formation of channel clusters in different membranes. Taken together these complementary experiments will provide a solid data base for an understanding of structure and function relations of simple channel proteins in variable lipid environments. We will obtain detailed information on the influence of different membrane properties on K+ channel function including gating and unitary conductance. The data will further show how the two partners, e.g. the membrane and the protein, compensate mismatches in the length of TMDs with respect to bilayer thickness without compromising function. The fact that the general structure of the viral K+ channels is similar to the pore structure of complex channels opens the possibility to extrapolate data from this research to physiologically relevant K+ channels.