Resolving the Structure of Ordered Domains in Single Hydrated Lipid Bilayers by New X-Ray Diffraction Methodology

Abstract

Saturated lipids spontaneously form rigid domain in lipid membranes. X-ray scattering from these domains indicate that their sizes vary between 2-60nm and that the lipids within are well ordered. This research characterizes the lipid packing and phase behavior of such domains in bilayers composed of sphingomyelin, ceramide, DPPC, POPC and cholesterol.Over the past 30 years, X-ray studies were performed on either lipid monolayers, or multilayers. Several attempts have been made over the past 20 years, to perform experiments on single lipid bilayers, all of which have failed due to the strong scattering of the bilayer's surrounding water. In order to overcome this challenge we have developed a new system, which enables measurements of single hydrated lipid bilayers using synchrotron radiation.1This research provided, for the first time, knowledge on the interactions between the opposing lipids of each leaflet at the core of the bilayer. Comparisons with lipid monolayers made of the same lipid composition showed that the phase behavior of the ordered domains differs greatly, indicating strong correlation between the opposing leaflets of the bilayer.2Large quantities of cholesterol monohydrate crystals are found in atherosclerotic plaques. Studies have shown that these crystals are an early cause of inflammation. We managed to characterize the conditions under which cholesterol molecules nucleate at the lipid bilayer. Results demonstrate that cholesterol nucleation depends on the lipid composition.2,3The study was awarded the 2011 Barenholz Prize for basic research on sphingolipids.1. Ziblat, R.; Leiserowitz, L.; Addadi, L., Angewandte Chemie-International Edition 2011, Accepted for publication.2. Ziblat, R.; Leiserowitz, L.; Addadi, L., J Am Chem Soc 2010, 132, (28), 9920-9927.3. Ziblat, R.; Kjaer, K.; Leiserowitz, L.; Addadi, L., Angewandte Chemie-International Edition 2009, 48, (47), 8958-8961.