Calendar Details

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Friday, April 12

Development and Uses of Asymmetric Lipid Vesicles for
Understanding Biomembrane Structure and Function

Erwin London, Stony Brook University, Stony Brook, NY
Biology and Soft Matter Division Seminar
2:00 PM — 3:00 PM, Joint Institute for Neutron Sciences (Building 8630), Room A-202
Contact: Frederick Heberle (heberlefa@ornl.gov), 865.576.8802

Abstract

The lipid bilayer in natural biomembranes is often highly asymmetric, with very different membrane lipids in the inner and outer monolayers (leaflets). However, almost all model membrane vesicle studies have made use of lipid vesicles with a symmetric lipid composition. We have developed a robust method to prepare asymmetric vesicles with a wide variety of lipid compositions and vesicle sizes. This method is based on use of cyclodextrins to exchange outer leaflet lipids between two populations of symmetric vesicles composed of different lipids, followed by separation of the desired vesicle population. A variety of spectroscopic methods to evaluate lipid asymmetry were developed. Experiments in which lipid acyl chain and polar headgroup structure was varied demonstrated that lipid structure can strongly influence whether asymmetry is unstable or highly stable (for days). Experiments with the membrane-inserting and pore forming protein perfringolysin O were carried out to investigate whether lipid asymmetry would affect membrane protein conformation. It was found that a natural degree of lipid asymmetry stabilizes the formation of a deeply-inserted intermediate conformation that does not form pores.