Monolayers to Bilayers to Membranes

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9603092 McConnell This research seeks to study putative liquid-liquid phase separations in lipid bilayer membranes, and their possible role in the function of biological membranes. The approach to these problems relies heavily on the previous finding in this laboratory of liquid-liquid phase separations in lipid monolayer membranes. The interest in liquid-liquid phase separations (along with their critical point properties) stems from their possible role in biological membranes, including membrane fusion, shape, trans membrane asymmetries, as well as enzymatic regulation of lipid composition. A major challenge in this work is to demonstrate unequivocally a one liquid to two liquid phase transition in a lipid bilayer membrane. A second challenge is to investigate the possibility that such transitions play a role in the regulation of lipid composition of biological membranes in response to physical or chemical factors (e.g., temperature or hormones). The techniques to be used in these studies rely heavily on fluorescence microscopy. The membrane that surrounds a living cell is very much like a very thin, two dimensional liquid. This liquid is quite complex being composed of many sorts of lipid molecules that together form this two-dimensional membrane. There is much experimental evidence that the physical properties and chemical compositions of these membranes are carefully regulated in living cells, but the relationship between the physical and chemical properties is very poorly understood, as is the role of these properties in the function of cells. The goal is to find out if liquid-liquid phase separations exist in these membrane liquids, and if they serve important biological functions.