Sum-Frequency Vibrational Spectroscopy Study of Membrane Asymmetry and the Transbilayer Movement of Lipids

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Professor John Conboy of the University of Utah is supported by the Analytical and Surface Chemistry Program to probe the movement of lipid species across cellular membranes by performing non-linear surface specific sum-frequency vibrational spectroscopy measurements on model lipid bilayers. The transbilayer movement of lipid, also known as lipid flip-flop or translocation, is a fundamentally important issue in molecular biology and has attracted interest among biologists and chemists for decades. Typically, lipid flip-flop has been investigated by nuclear magnetic spectroscopy (NMR), electron spin resonance spectroscopy and fluorescence spectroscopic techniques with model membrane systems such as vesicles and planar-supported lipid bilayers. To perform NMR or fluorescence measurements, lipids must be either spin-labeled or fluorescence-labeled. The labeling process will modify lipid physical properties and therefore has been considered as the drawback of these techniques. In this work, the PI is using a novel methodology to investigate lipid transbilayer movement that does not require the labeling. In addition, real-time monitoring of transbilayer movement can be attained. The PI is studying various properties of the flip-flop of perdeuterated lipids in planar membranes such as its activation energy, its dependence on lateral pressure, the effect of lipid structure and of membrane composition. In particular, the influence of cholesterol and selected membrane-active peptides on phospholipid flip-flop is being addressed. New findings drawn from the research could have a significant impact in molecular and cellular biology. Further, taking into account the increasing relevance of supported bilayers in nanotechnology and other fields, the proposal provides a very powerful and original approach to study and to optimize those films for various applications.