Effects of Lipid Polymerization on Membrane Mechanical Properties and Transmembrane Protein Activity

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Professor Scott Saavedra of the University of Arizona is supported by the Analytical and Surface Chemistry Program to investige the effects of photopolymerized, supported, planar lipid bilayers on the properties and activities of embedded transmembrane proteins (TMPs.) The hypothesis to be tested is that rather than fluidity, membrane elasticity is required to accommodate conformational changes in reconstituted TMPs. The PI plans to test this by studying the photo-initiated conformational change of a G protein coupled receptor (a type of TMP) in polymerized and non-polymerized planar supported lipid bilayers, and relating the extent of conformational change to the mechanical properties of the membrane. An instrument is being constructed to perform flash photolysis in an attenuated total reflection geometry on a planar integrated optical waveguide for monitoring formation and decay of the metarhodopsin II(MII)intermediate in planar supported lipid bilayers. The system to monitor MII will use a Nd:YAG laser for photolysis and an argon ion laser for probing MII. Second, a micropipette aspiration apparatus is being assembled to measure mechanical stretch properties of giant unilamellar vesicles. Finally, the effects on photoactivation of lipid monomer composition and degree of polymerization, as well as mechanical properties of the lipids, are being tested. Concentration ratios of different polymerizing components are being varied, as well as position of the cross linker along the lipid tails. Channels created in membranes by proteins amplify communication signals from cell to cell. The long-term goal of this research is to be able to harnass the sensitivity of these systems for drug discovery screening assays and as biosensors. In order to accomplish these goals, more fundamental research is needed about the role of the membrane in stabilizing proteins at surfaces.