Differences in the Modulation of Collective Membrane Motions by Ergosterol, Lanosterol, and Cholesterol: A Dynamic Light Scattering Study

¹ Universitaet Wuerzburg, Physikalisches Institut EP-5
² Universitaet Wuerzburg

^* To whom correspondence should be addressed. E-mail: bayerl{at}physik.uni-wuerzburg.de.

Submitted on July 28, 2004
Revised on October 20, 2004
Accepted on 30 November 2004

	Abstract

A dynamic light scattering (DLS) setup was used to study the undulations of freely suspended planar lipid bilayers, the so-called black lipid membranes (BLM), over a previously inaccessible range of frequency and wave number. A pure synthetic lecithin bilayer (1,2-dielaidoyl-sn-3-glycero-phoshatidylcholine (DEPC)) and binary mixtures of DEPC with 40 mol % of either cholesterol, ergosterol or lanosterol were studied. By analyzing the DLS data (oscillation and damping curves) in terms of transverse shear motion, we extracted the lateral tension and surface viscosity of the composite bilayers for each sterol. Cholesterol gave the strongest increase in lateral tension (about 6-fold) with respect to the DEPC control, followed by lanosterol (about 2-fold), and ergosterol (1.7 fold). Most interestingly, only cholesterol simultaneously altered the surface viscosity of the bilayer by almost two orders of magnitude while the other two sterols did not affect this parameter. We interpret this unique behavior of cholesterol as a result of its previously established out-of-plane motion which allows the molecule to cross the bilayer midplane, thereby effectively coupling the bilayer leaflets to form a highly flexible but more stable composite membrane.

Key Words: collective motion, dynamic light scattering, lateral tension, membrane, sterol, surface viscosity

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