Probing the Electrostatics of Lipid Bilayer Membranes

探讨脂质双层膜的静电

• 批准号: 0517937
• 负责人: Jason Hafner
• 金额: $ 30万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-08-01 至 2009-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0517937&HistoricalAwards=false
• 关键词: Probing; Electrostatics; Lipid; Bilayer; Membranes

Professor Jason Hafner of Rice University is supported by the Analytical and Surface Chemistry Program to investigate electrostatic potentials at membrane interfaces. The goal of the project is to understand charge distribution in lipid membranes and how that affects lipid aggregation and ultimately the structure of lipid membranes. The charge distribution and contributions from ion binding and dipoles from the lipids are being measured and mapped out using a novel charge-based nanoscale imaging technique developed by this group. The scanning probe instrument is called a Fluid Electric Force Microscope (FEFM), which is a version of an atomic force microscope (AFM) but uses the native electrostatic charge of the AFM tip to detect surface charge on the membrane. The AFM scans over the surface first to obtain topographic information from van der Waals interactions, then runs over the same trace again but now in a "lift-off" mode following the topography from the previous trace allowing the tip to now capture electrostatic information. The measurement technique has already been developed and has shown that it can distinguish between positively, negatively, and neutrally charged surfaces. In order to decipher and separate the multiple forces within the membrane (e.g., electrostatic, dipolar, hydrophobic, viscoelastic, and van der Waals interactions) that can influence both the topographic and charge mapping measurement, the team is characterizing the membrane's ion affinity using ion binding studies, dipole density through changes in the Debye length, and lipid phases in the membrane. They are achieving this by establishing the effective charge of the probe tip, controlling the solution ionic strength to ensure that the charge scan is run above the Debye length, measuring ion binding constants for different lipids with various ions, and determining the electrostatic contribution from lipid phases. Finally, the control of lipid bilayer dimensions by using the solution ionic strength is being examined. Electrostatic interactions are primary driving forces controlling molecular interactions at membrane interfaces. These play a critical role in determining the behavior and chemistry that takes place at the surfaces of all biological cells. Understanding the electrostatic charge distribution in the cell membrane is currently poor. Most of the attention is drawn towards specific interactions, such as protein-ligand recognition or raft formation through specific lipid combinations. Electrostatics are typically the domain of non-specific interactions. However, electrostatic interactions have astonishing effects on lipid phase transitions that could play a large role in raft formation in cell membranes, long range recognition properties that lead to specific host-guest complexation, cellular signaling for apoptosis, and facilitation of changes in membrane morphology during cell division or endo/exocytosis. Many studies have been performed to characterize the contribution of membrane charge with regard to these various phenomena, but they are mostly global or macroscopic measurements. To truly understand the contributions of electrostatic charge on cellular membranes, or even synthetic membrane systems, it is imperative to characterize the system at the nanoscopic level. It is highly likely that charge aggregation in nanoscale domains, such as in the partitioning of gangliosides in lipid rafts, is the activator for protein binding at specific sites in membranes. This project enables a first look into such phenomena with unprecedented resolution. The concepts that are being developed in this project would have a very broad impact on the biophysics community in their understanding of cellular membrane systems. Furthermore, research on lipid membrane materials is growing both at the scientific and technological fronts for drug delivery vehicles, sensor materials, biocompatible interfaces, detection array platforms, and as models for cell membranes. Understanding lipid organization is key to understanding how membrane materials function in each of these systems. Successful outcomes of this research may enable us to, for example, tune materials to selectively capture toxin molecules from solution for sensing and separations, or toggle ion channels for fuel cells or water purification.

莱斯大学的Jason Hafner教授得到了分析和表面化学计划的支持，该计划旨在研究膜界面的静电势。该项目的目标是了解脂膜中的电荷分布以及这如何影响脂膜聚集并最终影响脂膜的结构。利用该小组开发的一种新的基于电荷的纳米成像技术，正在测量和绘制电荷分布以及离子结合和脂类偶极的贡献。扫描探头仪器被称为流体电场显微镜(FEFM)，它是原子力显微镜(AFM)的一个版本，但使用AFM尖端的固有静电电荷来检测薄膜上的表面电荷。原子力显微镜首先在表面上扫描，从范德华相互作用中获得地形信息，然后再次运行相同的轨迹，但现在是在前一轨迹的地形之后以“起飞”模式运行，允许尖端现在捕获静电信息。这种测量技术已经开发出来，并表明它可以区分正电荷、负电荷和中性电荷的表面。为了破译和分离膜内会影响地形和电荷映射测量的多种作用力(例如静电、偶极、疏水、粘弹性和van der Waals相互作用)，该团队正在通过离子结合研究来表征膜的离子亲和力，通过改变德拜长度来表征膜的偶极密度，以及膜中的脂相。他们通过建立探针尖端的有效电荷，控制溶液离子强度以确保电荷扫描在德拜长度以上运行，测量不同脂类与各种离子的离子结合常数，以及确定脂相的静电贡献来实现这一点。最后，通过使用溶液离子强度来控制脂双分子层尺寸。静电相互作用是控制膜界面分子相互作用的主要驱动力。它们在决定所有生物细胞表面发生的行为和化学方面发挥着关键作用。目前对细胞膜中的静电电荷分布的了解很差。大部分的注意力被吸引到特定的相互作用上，例如蛋白质-配体识别或通过特定的脂类结合形成浮筏。静电学通常是非特定相互作用的领域。然而，静电相互作用对脂类相变具有惊人的影响，这可能在细胞膜上形成RAFT、导致特定主客体络合的远程识别特性、细胞凋亡信号以及促进细胞分裂或内吞/胞吞过程中膜形态的变化方面发挥重要作用。关于这些不同的现象，已经进行了许多研究来表征膜电荷的贡献，但它们大多是全局的或宏观的测量。为了真正了解静电对细胞膜，甚至合成膜系统的贡献，在纳米水平上表征该系统是非常必要的。纳米结构域中的电荷聚集，如在脂筏中神经节苷脂的分配，很可能是蛋白质结合在膜上特定位置的激活剂。这个项目使人们能够以前所未有的分辨率第一次看到这种现象。这个项目中正在发展的概念将对生物物理界理解细胞膜系统产生非常广泛的影响。此外，在药物输送载体、传感器材料、生物兼容接口、检测阵列平台以及作为细胞膜模型的科技前沿，对脂膜材料的研究都在不断增长。了解脂质组织是了解膜材料如何在这些系统中发挥作用的关键。例如，这项研究的成功结果可能使我们能够调整材料，从溶液中选择性地捕获毒素分子用于传感和分离，或者切换用于燃料电池或水净化的离子通道。