MICROSTRUCTURAL HETEROGENEITY IN MEMBRANES

本提案的目的是测试和应用一种新技术（荧光 寿命异质性分析），以确定是否存在 膜结构的微观异质性。 生命的力量 异质性分析是其检测的潜在灵敏度 短寿命的膜微区， 不同的阶段 这项技术的应用将首先 在简单模型膜系统中进行评估，其中结构 异质性是很好建立的。 然后，作为初始应用程序， 方法将被用来测试两个假设源于工作的 上一个资助期：1）一个跨膜蛋白质都命令和 紊乱其局部脂质环境，和2）胆固醇诱导 流体脂质双层中量热法检测不到的局部区域。 新的应用将使用寿命分析来检测微观结构 被认为与两个关键的细胞过程，膜融合， 和磷脂跨膜迁移。 除了荧光 寿命分析，适当的热力学技术（扫描 量热法，稳态探针荧光，化学标记， 冷冻断裂电子显微镜）将用于检查双层 与这些事件相关的结构特征， 系统. 在聚乙二醇诱导的膜融合的情况下，这些 测量将测试不同结构的假设， 这些特征与两个至关重要的、以前不可分割的 融合过程中的中间状态：双层紧密贴壁和 双层不稳定 在阳离子诱导的情况下， 磷脂酰甘油跨双层再分布，结果将测试两个 假设：1）跨双层再分布涉及两个组件 金属离子和脂质双层之间的相互作用和2）这种相互作用 诱导脂质双层中的反胶束样局部结构。

The aim of this proposal is to test and apply a new technique (fluorescence lifetime heterogeneity analysis) for identifying the existence of microheterogeneity in membrane structure. The power of lifetime heterogeneity analysis is its potential sensitivity for detecting short-lived membrane microdomains which do not appear as thermodynamically distinct phases. The applicability of this technique will first be evaluated in simple model membrane systems in which structural heterogeneity is well established. Then, as initial applications, this method will be used to test two hypotheses stemming from work of the previous grant period: 1) that a trans-membrane protein both orders and disorders its local lipid environment, and 2) that cholesterol induces calorimetrically undetectable local domains in fluid lipid bilayers. New applications will use lifetime analysis to detect microstructures thought to be associated with two key cellular processes, membrane fusion and phospholipid trans-membrane migration. In addition to fluorescence lifetime analysis, appropriate thermodynamic techniques (scanning calorimetry, steady-state probe fluorescence, chemical labeling, freeze-fracture electron microscopy) will be used to examine bilayer structural features associated with these events in well-defined, model systems. In the case of polyethyleneglycol-induced membrane fusion, these measurements will test the hypothesis that different structural characteristics are associated with two crucial and previously inseparable intermediate states in the fusion process: bilayer close apposition and bilayer destabilization. In the case of cation-induced phosphatidylglycerol transbilayer redistribution, results will test two hypotheses: 1) transbilayer redistribution involves a two-component interaction between a metal ion and a lipid bilayer and 2) this interaction induces inverted micelle-like local structures in the lipid bilayer.