Lipid phase segregation leading to the formation of nanoscale lipid rafts is important in many cellular processes, including signaling and viral docking. Existing membrane model systems do not exhibit this nanoscale raft formation phenomenon: phase segregation in model membranes takes place on much larger scales. We are designing biomimetic systems that reproduce the nanoscale phase separation behavior observed in cells. These systems promise to be useful tools for studying the biophysics of lipid rafts and raft-protein interactions as well as platforms for screening potential raft-targeted drugs.
 We are studying lipid behavior in constructs consisting of large (~50 micrometers) spherical vesicles with hydrogel interiors. Connectivity between the lipid bilayer and the hydrogel mimics the connectivity of the cell membrane and the actin cytoskeleton, allowing us to study the effects of this connectivity on lipid structure formation.
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 Detection of lipid raft formation by fluorescence self-quenching. Labeled saturated lipids fluoresce at full intensity when distant from one another, but when they are concentrated in rafts, the labels self-quench and the detected fluorescence decreases.
 Fluorescence self-quenching as a function of cholesterol concentration. Raft formation is triggered by temperature transition from above to below the miscibility transition temperature. Since raft formation is dependant on the presence of cholesterol, self-quenching can only be seen in model membranes with cholesterol above a critical concentration. |