Alamethicin-lipid interaction studied by energy dispersive X-ray diffraction

A detailed knowledge of the interaction between bacterial membranes and antibiotics provides important information to prevent high levels of antibiotic resistance exhibited by pathogenic strains. We investigated by energy dispersive X-ray diffraction (EDXD) the structure ordering of dioleoyl-phosphatidylcholine (DOPC) lipid interacting with antimicrobial peptide alamethicin, varying the lipid/peptide (L/P) molar ratio under two different hydration levels.In conditions of full hydration (100%) we found that the bilayer thickness is constant between L/P = 20 and L/P = 80 indicating that in this range, the system has reached the threshold value for the channel formation, while at the relative hydration of 45% a linear decrease of the bilayer thickness as function of L/P was revealed. The kinetic Study of the complex alamethicin-DOPC at different L/P values, shows that the Bragg peak energy variation versus the hydration time has a biexponential behavior characterized by two different time constants. (C) 2008 Elsevier B.V. All rights reserved.