Interleaflet Coupling Effects in Supported Lipid Membranes

Cellular membranes contain amphiphilic lipid molecules that self-assemble into a bilayer structure. In biological membrane systems, there has been considerable interest in phase-separated domains termed lipid rafts. These domains play an important role in cellular functions as organized centers for signaling molecules such as membrane proteins and influence membrane fluidity. Fundamental knowledge of a lipid domainâ??s biophysical properties in model systems informs a greater understanding of their functions and properties in living systems. In this research project, we are investigating the properties of phospholipid bilayers by using substrate-supported lipid bilayers (SLBs) as model systems. In these model systems, domains are almost exclusively observed as being coupled across the bilayer (i.e. in phase-registry), suggesting that interleaflet interactions play a notable role in domain formation. To investigate the strength of interleaflet coupling in SLBs, we aim to develop an electrophoresis-based method to measure the coupling between the leaflets. Electrophoresis is conventionally used in biology to separate macromolecules based on size and electrostatic charge by application of an external electric field. In contrast, we attempt to use applied electric fields to induce directed, lateral diffusion of charged lipids and lipid domains. By monitoring the electrophoretic response of domains, we seek to characterize the relative strength of coupling interactions in different SLB systems. In the future, we plan to investigate the differences in characteristics of a membrane deposited on a fluid-phase and gel-phase monolayer in comparison to one deposited on a covalently grafted monolayer, comparing a dynamically responsive phospholipid system with a mimetic covalently grafted system. Additionally, we would like to explore the implications of depositing phase separated monolayers on inner leaflets that are not normally prone to domain formation. By observing microstructural changes in phase separated monolayers before and after deposition, we intend to gather information regarding the role of coupling in sustaining preexisting domains.