Influence of Cholesterol on Phase Behavior and Nonrandom Mixing of Membrane Components

这个项目的目标是研究非随机混合的热力学基础的脂质双层模型生物膜。 该项目有四个主要的概念要素：（一）三组分双层脂质混合物作为哺乳动物质膜的外小叶和内小叶的模型。 这些3-组分混合物足够复杂以模拟真实的生物膜，但在化学上是明确定义的;（ii）使用几种独立的、互补的方法来彻底绘制和表征这些模型膜的组成相行为;（iii）真实的生物膜是不对称的：为了弥合化学简单模型和真实的生物膜之间的差距，将研究也是不对称的模型双层;（iv）活细胞（包括天然膜筏）的质膜行为将通过在模型系统中开发的方法进行研究，并根据模型系统获得的相图进行分析。 在实验上，这项工作涉及大量的数据集的荧光共振能量转移和？准分子/单体测量，找到脂质相边界和分配行为的荧光探针。 共聚焦荧光显微镜将用于可视化和识别共存相。 胆固醇是哺乳动物细胞膜中含量最多的一种脂质。 尽管如此，胆固醇与邻近膜分子相互作用的方式仍然不清楚。 已知胆固醇与其他膜脂质非随机混合，但在大多数情况下，对胆固醇的横向分布以及胆固醇影响其他膜组分横向分布的方式缺乏清晰的理解。 目前的非随机混合的生物膜，“筏模型”的胆固醇丰富的补丁浮动在胆固醇穷人双层，很可能会改善这项研究项目。 此外，为了促进科学教育和培训，一批本科生将接受脂质物理化学和荧光光谱学的讲座，然后进行脂质分析化学，脂质有机合成以及光谱和显微镜技术的系统培训，然后他们将在分配的独立研究中使用。

The goal of this project is to study the thermodynamic basis for nonrandom mixing in lipid bilayers that model biomembranes. The project has four main conceptual elements: (i) 3-component bilayer lipid mixtures serve as models for the outer and the inner leaflets of mammalian plasma membranes. These 3-component mixtures are sufficiently complex to model real biomembranes, yet are chemically well-defined; (ii) Several independent, complementary methods are used to thoroughly map and characterize the compositional phase behavior of these model membranes; (iii) Real biomembranes are asymmetric: model bilayers that are also asymmetric will be studied in order to bridge the gap between the chemically-simple models and real biomembranes; (iv) Behavior of the plasma membranes of living cells, including the nature membrane rafts, will be investigated by the methods developed in the model systems and analyzed in terms of the phase diagrams obtained for the model systems. Experimentally, this work involves large data sets of fluorescence resonance energy transfer and perylene excimer/monomer measurements to find the lipid phase boundaries and the partition behavior of fluorescent probes. Confocal fluorescence microscopy will be used to visualize and identify coexisting phases. New procedures will be developed in order to prepare asymmetric lipid bilayers.Cholesterol is the single most abundant lipid species in mammalian plasma membranes. Nonetheless, the way cholesterol interacts with neighboring membrane molecules has remained obscure. Cholesterol is known to mix nonrandomly with other membrane lipids, and yet in most cases a clear understanding is missing for the lateral distribution of cholesterol, and the way cholesterol influences the lateral distribution of other membrane components. A current picture of nonrandom mixing in biomembranes, the "raft model" of cholesterol-rich patches floating within a cholesterol-poor bilayer, is likely to be improved by this research project. In addition, in order to promote scientific education and training, a group of undergraduate students will receive lectures in lipid physical chemistry and fluorescence spectroscopy, followed by systematic training in lipid analytical chemistry, lipid organic synthesis, and spectroscopic and microscope techniques, which they will then use in their assigned independent research.