Determining the Structure of Biological Membranes through Adhesive Emulsions

细胞的膜将细胞内部的内容物与周围的液体隔开。半透膜由脂质双层和各种蛋白质组成，这些蛋白质能够使细胞间传递信号，并控制通过膜的物质交换。脂类和蛋白质之间的相互作用有助于蛋白质在膜上的空间组织。已经广泛地研究了双层的每个小叶之间的相互作用；本项目侧重于小叶之间的横向相互作用。该项目将开发一种新的实验方法，使用相互挤压的脂膜涂层液滴来形成合成脂类双层膜。测量相互作用的液滴和膜的某些特性将允许定量地确定横向脂类相互作用的能量学。这项研究的发现将显示双层的两个小叶的组成差异如何影响细胞功能，这可能会启发新的治疗方法来检测和抗击疾病。该项目将为来自几个工程学科的研究生提供参与高度跨学科研究的机会。该项目还将通过佐治亚大学现有的几个项目吸引高中生和本科生参与工程研究，这些项目加强了来自代表性不足群体的学生在工程研究中的参与。虽然很好地描述了由于横向脂质-脂质相互作用而形成的细胞膜中脂质亚域的形成，但随之而来的脂质亚域的跨膜耦合还没有得到充分的探索。该项目将利用液滴界面双层的流体性质，通过张力测量和电生理学相结合的方法来研究这些现象。覆盖有有序脂质单层的纳升水滴将被操纵接触，以形成每个小叶中不同组成的模型脂质双层膜。在膜上施加电场会同时产生电压缩和电润湿，导致膜同时变薄和膨胀。在此过程中，对膜面积和接触角的目测测量将提供膜厚度和表观双层张力的精确值，而无需额外的校准。电压过程中膜张力的变化将反映脂叶内和脂叶之间的脂类相互作用。将使用可光聚合的脂类创建模型筏或脂质亚域，并将跟踪电压缩过程中膜性质的变化，作为这些亚域在膜小叶之间的不对称分布的函数。这一方法将提供由小叶不对称产生的错配能量的实验测量，该不对称被假设为驱动类脂结构域的配置。该项目将为工程学研究生提供跨学科培训，重点是电生理学、张力测量、界面化学、建模和仪器。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The membrane of a cell separates the cell's interior contents from the surrounding fluid. The semi-permeable membrane is composed of a lipid bilayer and various proteins that enable cell-cell signaling and control exchange of material through the membrane. Interactions among lipids and proteins help organize the proteins spatially in the membrane. Interactions within each leaflet of the bilayer have been studied extensively; this project focuses on transverse interactions between the leaflets. The project will develop a new experimental approach that uses lipid-coated droplets pressed against each other to form synthetic lipid bilayer membranes. Measurements of certain characteristics of the interacting droplets and the membrane will allow the energetics of transverse lipid interactions to be determined quantitatively. Findings from this research will show how differences in the compositions of the two leaflets of a bilayer affect cell function, which could inspire new therapeutics to detect and combat disease. The project will provide opportunities for graduate students from several engineering disciplines to participate in highly interdisciplinary research. The project will also engage high school and undergraduate students through several existing programs at the University of Georgia that enhance participation of students from underrepresented groups in engineering research.While the formation of lipid subdomains in cellular membranes due to lateral lipid-lipid interactions is well characterized, the accompanying cross-membrane coupling of lipid subdomains is underexplored. This project will exploit the fluidic properties of droplet interface bilayers to study these phenomena through a combination of tensiometry and electrophysiology. Aqueous nanoliter droplets coated with ordered lipid monolayers will be manipulated into contact to form model lipid bilayer membranes with varying compositions in each leaflet. An imposed electric field across the membrane will produce both electrocompression and electrowetting, causing the membrane to simultaneously thin and expand. Visual measurements of the membrane area and the angle of contact during this process will provide accurate values of the membrane thickness and the apparent bilayer tension without additional calibration. Changes in the membrane tension during electrocompression will reflect lipid-lipid interactions within and between the lipid leaflets. Model rafts or lipid subdomains will be created using photopolymerizable lipids, and changes in the membrane properties during electrocompression will be tracked as a function of the asymmetric distribution of these subdomains between the membrane leaflets. This approach will provide experimental measurements of the mismatch energy generated by leaflet asymmetry, which has been hypothesized to drive collocation of the lipid domains. The project will provide interdisciplinary training for a graduate student in engineering, with emphasis on electrophysiology, tensiometry, interfacial chemistry, modeling, and instrumentation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.