INTERACTION OF FUSIDIC ACID WITH LIPID MEMBRANES: IMPLICATIONS TO THE MECHANISM OF ANTIBIOTIC ACTIVITY

¹ Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, U
² Laboratory of Analytical Chemistry, Department of Chemistry, University of Helsinki, Finland
³ Department of Applied Mathematics, The University of Western Ontario, London (ON), Canada
⁴ University of Helsinki Institute of Biomedicine
⁵ Biophysics and Statistical Mechanics Group, Laboratory for Computational Engineering, HUT, Finland
⁶ Department of Ophthalmology, University of Helsinki, Finland
⁷ Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology, Finland
⁸ Department of Ophthalmology, University of Helsinki

^* To whom correspondence should be addressed. E-mail: holopainen.juha{at}gmail.com.

Submitted on March 8, 2006
Revised on May 9, 2006
Accepted on 6 June 2006

	Abstract

We have studied the effects of cholesterol and steroid-based antibiotic fusidic acid (FA) on the behavior of lipid bilayers using a variety of experimental techniques together with atomic-scale molecular dynamics (MD) simulations. Capillary electrophoretic measurements showed that FA was incorporated into fluid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes. Differential scanning calorimetry in turn showed that FA only slightly altered the thermodynamic properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers whereas cholesterol abolished all endotherms when the mole fraction of cholesterol (X_chol) was >0.20. Fluorescence spectroscopy was then used to further characterize the influence of these two steroids on DPPC large unilamellar vesicles. In the case of FA, our result strongly suggested that FA was organized into lateral microdomains with increased water penetration into the membrane. For cholesterol/DPPC mixtures fluoresecence spectroscopy results were compatible with the formation of the liquid-ordered phase. A comparison of FA and cholesterol induced effects on DPPC bilayers through atomistic MD simulations showed that both FA and cholesterol tend to order neighboring lipid chains. However, the ordering effect of FA was slightly weaker than that of cholesterol, and especially for deprotonated FA the difference was significant. Summarizing, our results show that FA is readily incorporated into the lipid bilayer where it is likely to be enriched into lateral microdomains. These domains could facilitate the association of elongation factor -G into lipid rafts in living bacteria enhancing markedly the antibiotic efficacy of FA.

Key Words: capillary electrophoresis, computer simulations, differential scanning calorimetry, fluorescence spectroscopy, lipid-drug interactions

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