Influence of Cholesterol on Phase Behavior and Nonrandom Mixing of Membrane Components

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Feigenson, Gerald W.MCB 0077630The overall goal of this project is to understand the role of cholesterol in biological membranes. This project has four main conceptual elements: (i) 3-component lipid mixtures, containing cholesterol, will serve as chemically simple experimental models of mammalian plasma membranes; (ii) Several independent, complementary methods will be used to thoroughly map and characterize the compositional phase behavior of these model membranes; (iii) Based on the observed phase behavior, Monte Carlo simulations will be used to find the dominant microscopic lipid-lipid interaction energies; and (iv) The lateral distributions of other membrane components will be studied in these well-characterized systems, shedding light on the nature of cholesterol-rich "detergent resistant membranes." Experimentally, this project involves x-ray diffraction to find phase boundaries; electron spin resonance to map order parameters of the phases; pyrene excimer/monomer ratios and fluorescence resonance energy transfer to find phase boundaries and to measure partitioning between phases; confocal fluorescence microscopy to visualize coexisting phases; and computer simulations to evaluate the thermodynamic implications of microscopic interaction models and to generate pictures of lateral distributions. Although cholesterol is the single most abundant lipid species in mammalian plasma membranes, the underlying nature of its interactions with neighboring membrane molecules has remained obscure. This research will provide an in-depth physical understanding of these underlying lipid-lipid interactions and could therefore have a very significant impact on the field of signal transduction.