Eur. Phys. J. E 5, 485-497 (2001)
Simulation study of lateral diffusion in lipid-sterol bilayer mixtures
J.M. Polson1, I. Vattulainen2, H. Zhu1 and M.J. Zuckermann1, 31 Centre for the Physics of Materials, Department of Physics, McGill University, Rutherford Building, 3600 Rue Université, Montréal, PQ, Canada H3A 2T8
2 Department of Chemistry, Building 206, Technical University of Denmark, 2800 Lyngby, Denmark
3 School of Physics, University of New South Wales, Kensington Campus, Old Main Building, Kensington, Sydney 2052, Australia
Ilpo.Vattulainen@csc.fi
(Received 24 November 2000 and Received in final form 30 April 2001)
Abstract
We employ off-lattice Monte Carlo simulations to study lateral diffusion
in lipid-sterol bilayers using a two-dimensional model system which has
been designed to simulate the experimental phase diagrams of both
lipid-cholesterol and lipid-lanosterol systems. We focus on
the effects of varying sterol concentration and temperature on the
tracer diffusion coefficient, D, which characterizes the lateral
motion of single tagged lipids in a bilayer. Generally, we find that
increasing the cholesterol concentration suppresses D due to an
increased conformational ordering of lipid chains. We argue that this
effect competes with an increase in the average free area per lipid,
which favours an increase in D. At temperatures close to the main
transition temperature, the competition between the two effects leads
to intriguing behavior of D. Overall, the model results are in
excellent qualitative agreement with available experimental results
for lipid-cholesterol mixtures. Additional studies of a model
lipid-lanosterol system, for which experimental diffusion results
are not available, predict that the presence of lanosterol has a
smaller effect than cholesterol on reducing D relative to the
pure lipid system. We conclude that the molecular model employed
contains the essential features required to describe many of the
qualitative features of the lateral diffusion behavior in
lipid-sterol systems.
87.16.Dg - Membranes, bilayers, and vesicles.
87.16.Ac - Theory and modeling; computer simulation.
87.15.Vv - Diffusion.
87.14.Cc - Lipids.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
