MEMBRANE MEDIATED PROTEIN INTERACTION

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 在水的存在下，取向的脂质膜在平坦和光滑的表面附近自组装，形成近晶-C液晶结构，其中水插在由脂质分子形成的双层之间。通过将水合脂质夹在两种基质之间，可以获得高度对齐的脂质膜的几平方毫米大的无缺陷单域。使用薄的氮化硅窗口作为对准衬底的传输SAXS实验对这样的样品是可能的。在Bealine 4-2处可用的小尺寸和高强度的光束与大的无缺陷域尺寸一起允许探测膜平面中的结构。在这个项目中，我们研究了膜嵌入肽之间的最近邻距离的变化依赖于脂质的厚度和肽浓度。我们发现，蛋白质之间的平均距离增加的双层厚度。这种效应归因于由于增加的疏水错配而增加的肽之间的膜介导的排斥相互作用。可以使用肽的已知形状因子和理论结构因子的乘积来拟合数据，所述理论结构因子假设嵌入的肽之间的硬核排斥而计算。硬核排斥被认为是一个适当的模型与最短的脂链的系统。脂质链长度的增加产生肽和脂质的疏水长度之间的错配，导致肽之间的较长范围的膜介导力的开始。为了将这些额外的力纳入核心结构因子，目前正在对当前模型进行扰动扩展。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In the presence of water aligned lipid membranes self-assemble in the vicinity of flat and smooth surfaces forming a smectic-C liquid crystal structure with water intercalated between the bilayers formed by the lipid molecules. By sandwiching hydrated lipids in between two substrates one can achieve several square-millimeter large defect-free monodomains of highly aligned lipid membranes. Using thin silicon-nitride windows as alignment substrate transmission SAXS experiments on such samples are possible. The small size and high intensity of the beam available at bealine 4-2 together with the large defect free domain size allows to probe the structure in the plane of the membrane. In this project we investigated the change in the nearest neighbor distance between membrane embedded peptides in dependence on the thickness of the lipid and the peptide concentration. We find that the average distance between the proteins increases with increasing thickness of the bilayer. This effect is attributed to the increased membrane mediated repulsive interaction between the peptides due to the increased hydrophobic mismatch. The data can be fitted using the product of the known formfactor of the peptide and a theoretical structure factor calculated assuming hard-core repulsion between the embedded peptides. The hard core repulsion was found to be an adequate model for the system with the shortest lipid chains. An increase in the lipid chain length producing a mismatch between the hydrophobic lengths of the peptide and the lipid causes the onset of longer ranged, membrane mediated forces between the peptides. In order to include these additional forces into the hard-core structure factor a perturbation extension of the current model is currently being pursued.