Determining the Structure of Biological Membranes through Adhesive Emulsions

University Of Georgia Research Foundation Inc, Athens GA

Investigators

Abstract

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.