A membrane, only two molecules thick, surrounds all cells and is responsible for controlling the passage of materials in and out of the cell in a selective manner. Our current understanding of the structure and dynamics of cellular membranes emerged in the early 1970?s. However, there is still much we do not know about this seemingly simple "shell" which makes life as we know it possible. A central issue in biology is the movement of molecules across the cellular membrane. This "translocation" is important in the infection of living cells by viruses, the functioning of antibiotics, antiseptics and drugs, and the regulation and growth of cells. There have been a number of studies attempting to find out just how this happens. There are many theories, but no conclusions. Using methods developed in the investigator's laboratory, a novel analytical approach was invented to selectively probe lipid translocation and membrane composition in a lipid bilayer (model cell membrane). The goal of the proposed research is to use this new tool to address some of the central issues concerning molecular motion in membranes. Facilitating an interest in chemistry, biology, physics and mathematics is also an integral part of the proposed studies, with efforts underway to create an innovative science and math education facility at the University of Utah, which will reach out to high school students, college freshmen and the general public, to expand their awareness and knowledge of science.
With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. John Conboy from the University of Utah to unravel the complex interplay between the movement of lipid species across the cellular membrane and the establishment of lipid compositional asymmetry. A full understanding of the mechanism by which membrane asymmetry is achieved and maintained in cellular systems has not been realized to date; primarily due to the difficulty of studying membrane biophysical phenomena in a non-destructive or non-perturbing fashion. It has been suggested that lipid membrane asymmetry is maintained by unidirectional lipid transporters, in conjunction with a high energetic barrier to translocation which limits the rate at which lipids might spontaneously translocate across the membrane. However, such a putative flippase has yet to be identified, and a growing number of publications demonstrate cases of rapid spontaneous translocation of phospholipids. The connection between lipid compositional asymmetry and flip-flop in planar supported lipid bilayers will be explored using a novel application of sum-frequency vibrational spectroscopy (SFVS) developed by the PI to selectively probe the asymmetry in a planar-supported lipid bilayer (PSLB). This new surface analytical method allows for the direct detection of lipid flip-flop without the need for a fluorescent or spin-labeled lipid probe, which can alter the measured translocation rates. The goal of this research is to use this surface analytical tool to address some of the central issues concerning the transbilayer movement and establishment of lipid asymmetry in bilayer systems. In addition, the coupling of lipid flip-flop energetics to the establishment of lipid asymmetry will also be explored. These studies are aimed at providing physical insight into the mechanism of lipid compositional asymmetry.
