Towards a More Accurate Model of the Plasma Membrane: Influence of Cholesterol on Phase Behavior and Nonrandom mixing of Membrane Components

外膜是活细胞与外界接触的地方，是一个复杂的结构。 该项目将产生动物细胞外膜的新图像，这将增加对细胞如何响应小分子激素结合，与其他细胞或生物体友好或不友好接触，甚至病毒感染等事件的理解。 这种膜的复杂性包括大量不同的成分，脂质和蛋白质，以及膜的分层结构，双层的每一半都是不同的，但与另一半相通。 这些研究的一个目标是测量双层的每一半如何与另一半通信。 总的来说，这项研究将集中在两个行为的个别脂质和蛋白质，以及对行为的大集合的脂质和蛋白质，称为“相域”。 该项目旨在开发简化的细胞膜模型，使用定义明确的脂质和肽的双层混合物来模拟活细胞膜的行为。 这些研究的一个重要方面将是培养本科生、研究生和博士后在膜研究中非常有用的专业方法。这个项目将导致动物细胞质膜具有图案形态的新图片，可能下降到几十纳米的尺度。这种新的观点很可能取代目前定义不太明确的观点，即有序的木筏漂浮在无序的脂质海洋中。该项目的目标是：（i）开发具有与偶极排斥和曲率能竞争的界面线张力的竞争相互作用模型，使得能够预测数十纳米尺度的相模式;（ii）测量线张力并模拟线张力以使得能够预测纳米尺度的相模式;（iii）测量作为动物细胞质膜的良好模型的脂质混合物的纳米域尺寸;（iv）发现膜蛋白如何响应和改变脂质相模式;和（v）发现小叶如何在不对称脂质双层囊泡中相互影响。竞争相互作用模型将通过竞争场的蒙特卡罗模拟来实现。分子动力学模拟将使用GROMACS，包括United Atom或Coarse Grain。纳米畴图案特征的尺寸将通过小角中子散射的分析来测量。 宏观尺度下的相形态和线张力将通过巨单层囊泡（GUV）的荧光显微镜成像来确定。 这个项目的一个主要目标将是培养本科生，研究生和博士后在专门的计算和实验方法，是如此有用的膜研究。

The outer membrane, the place where a living cell is in contact with the outside world, is a complex structure. This project will result in a new picture of animal cell outer membranes, which will increase understanding of how a cell responds to events such as binding of small molecule hormones, contacts with other cells or organisms friendly or unfriendly, and even viral infection. The complexity of this membrane includes the large number of different components, both lipid and protein, as well as the membrane's layered structure, with each half of the bilayer being different, yet in communication with the other half. One goal of these studies is to measure how each half of the bilayer communicates with the other half. Overall, this research will focus on both the behavior of individual lipids and proteins, as well as on the behavior of large collections of lipids and proteins, termed "phase domains". This project aims to develop simplified models of the cell membrane, using well-defined bilayer mixtures of lipids and peptides to mimic the behaviors of live cell membranes. An important aspect of these studies will be to train undergraduates, graduate students, and postdocs in the specialized methods that are so useful in membrane research.This project will result in a new picture of animal cell plasma membranes as having patterned morphology, possibly down to the scale of tens of nanometers. This new view is likely to replace the current, less well-defined view of ordered rafts floating in a sea of disordered lipids. The project objectives are to: (i) develop a competing interactions model with interfacial line tension competing with dipolar repulsion and curvature energies, enabling prediction of phase patterns at the tens of nanometer scale; (ii) measure line tension and simulate line tension to enable predictions at the nanometer scale; (iii) measure nanodomain size for lipid mixtures that are good models of animal cell plasma membranes; (iv) discover how membrane proteins respond to and modify the lipid phase patterns; and (v) discover how leaflets influence each other in asymmetric lipid bilayer vesicles. The competing interactions model will be implemented by Monte Carlo simulations of competing fields. Molecular dynamics simulations will use GROMACS, both United Atom or Coarse Grain. Size of nanodomain pattern features will be measured by analysis of small angle neutron scattering. Phase morphology and line tension at the macro scale will be determined via fluorescence microscopy imaging of giant unilamellar vesicles (GUVs). A major objective of this project will be to train undergraduates, graduate students, and postdocs in the specialized computational and experimental methods that are so useful in membrane research.