Advancing the Measurement of Lipid Transbilayer Exchange

只有两个分子厚的膜包围着所有细胞，负责以选择性的方式控制物质进出细胞。我们目前对细胞膜结构和动力学的理解出现在20世纪70年代初。然而，对于这个看似简单的“外壳”，我们仍然有很多不了解的地方，它使我们所知道的生命成为可能。生物学的一个中心问题是分子在细胞膜上的运动。这种“易位”在活细胞被病毒感染、抗生素、防腐剂和药物的功能以及细胞的调节和生长中都很重要。有许多研究试图找出这是如何发生的。有很多理论，但没有结论。利用研究者实验室开发的方法，发明了一种新的分析方法来选择性地探测脂质双分子层（模型细胞膜）中的脂质易位和膜组成。提出的研究目标是使用这个新工具来解决一些关于膜中的分子运动的核心问题。促进对化学、生物、物理和数学的兴趣也是拟议研究的一个组成部分，正在努力在犹他大学创建一个创新的科学和数学教育设施，这将接触到高中生、大学新生和普通公众，扩大他们的科学意识和知识。通过这一奖项，化学部门的生命过程化学项目资助了犹他大学的John Conboy博士，以揭示脂质在细胞膜上的运动和脂质组成不对称之间复杂的相互作用。迄今为止，对细胞系统中膜不对称形成和维持的机制的充分理解尚未实现；主要是由于研究膜生物物理现象的困难，以一种非破坏性或非干扰的方式。有人认为，脂质膜的不对称性是由单向脂质转运蛋白维持的，同时，脂质转运的高能量屏障限制了脂质自发跨膜转运的速度。然而，这种假定的翻转酶尚未被确定，并且越来越多的出版物证明了磷脂快速自发易位的案例。利用PI开发的新应用和频率振动光谱（SFVS）来选择性地探测平面支撑脂质双分子层（PSLB）中的不对称性，将探索平面支撑脂质双分子层中脂质组成不对称与触发器之间的联系。这种新的表面分析方法允许直接检测脂质触发器，而不需要荧光或自旋标记的脂质探针，这可以改变测量的易位率。本研究的目的是利用这种表面分析工具来解决一些关于跨双分子层运动和双分子层系统中脂质不对称建立的核心问题。此外，脂质翻转能量学与脂质不对称建立的耦合也将被探讨。这些研究旨在为脂质组成不对称的机制提供物理见解。

A membrane, only two molecules thick, surrounds all cells and is responsible for controlling the passage of materials in and out of the cell in a selective manner. Our current understanding of the structure and dynamics of cellular membranes emerged in the early 1970?s. However, there is still much we do not know about this seemingly simple "shell" which makes life as we know it possible. A central issue in biology is the movement of molecules across the cellular membrane. This "translocation" is important in the infection of living cells by viruses, the functioning of antibiotics, antiseptics and drugs, and the regulation and growth of cells. There have been a number of studies attempting to find out just how this happens. There are many theories, but no conclusions. Using methods developed in the investigator's laboratory, a novel analytical approach was invented to selectively probe lipid translocation and membrane composition in a lipid bilayer (model cell membrane). The goal of the proposed research is to use this new tool to address some of the central issues concerning molecular motion in membranes. Facilitating an interest in chemistry, biology, physics and mathematics is also an integral part of the proposed studies, with efforts underway to create an innovative science and math education facility at the University of Utah, which will reach out to high school students, college freshmen and the general public, to expand their awareness and knowledge of science. With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. John Conboy from the University of Utah to unravel the complex interplay between the movement of lipid species across the cellular membrane and the establishment of lipid compositional asymmetry. A full understanding of the mechanism by which membrane asymmetry is achieved and maintained in cellular systems has not been realized to date; primarily due to the difficulty of studying membrane biophysical phenomena in a non-destructive or non-perturbing fashion. It has been suggested that lipid membrane asymmetry is maintained by unidirectional lipid transporters, in conjunction with a high energetic barrier to translocation which limits the rate at which lipids might spontaneously translocate across the membrane. However, such a putative flippase has yet to be identified, and a growing number of publications demonstrate cases of rapid spontaneous translocation of phospholipids. The connection between lipid compositional asymmetry and flip-flop in planar supported lipid bilayers will be explored using a novel application of sum-frequency vibrational spectroscopy (SFVS) developed by the PI to selectively probe the asymmetry in a planar-supported lipid bilayer (PSLB). This new surface analytical method allows for the direct detection of lipid flip-flop without the need for a fluorescent or spin-labeled lipid probe, which can alter the measured translocation rates. The goal of this research is to use this surface analytical tool to address some of the central issues concerning the transbilayer movement and establishment of lipid asymmetry in bilayer systems. In addition, the coupling of lipid flip-flop energetics to the establishment of lipid asymmetry will also be explored. These studies are aimed at providing physical insight into the mechanism of lipid compositional asymmetry.