Cholesterol, a lipid biosynthesized within cells, is known to have a profound effect on cell membranes. An essential structural component, cholesterol not only increases bilayer stiffness and thickness, but plays a key role in facilitating membrane organization. There is growing evidence that lipids and proteins self-organize in order to bring about subcompartmentalization as a means of organizing the bioactivity of cell membranes. By laterally segregating membrane constituents, cholesterol is responsible for the creation of two co-existing phases: a thicker, liquid-ordered (Lo ) phase, in which cholesterol resides, and a thinner, liquid-disordered (LD) phase. The areas in the membrane containing higher concentrations of cholesterol and sphingolipids are known as lipid rafts, or microdomains.
In this research, different mole fractions of cholesterol in planar lipid bilayers were studied in order to discover the point at which membrane heterogeneity becomes present as a result of the formation of lipid rafts and to quantify changes in a functional protein in these varying lipid environments. The experiments applied electrophysiology to determine the impact of cholesterol on lipid bilayer physical properties through the incorporation of gramicidin A (gA), in which gA lifetimes were used as a readout. It is expected that two distinct gA lifetimes will be observed if lipid rafts are present in the model membranes and affect gA channels differently based on where the channels are localized. One gA lifetime duration would be representative of channels in cholesterol-enriched areas (lipid rafts), while the other lifetime duration would be in areas of low cholesterol concentration. The findings of this research have the potential to provide insight into the specific effects of cholesterol on protein activity and membrane organization that can be used to enhance the beneficial effects of prescription drugs.
Sydney Strunk, ’17
Sponsor: Jai Shanata