The Synergistic Effects of Lipids and Peptides on Membrane Dynamics

Abstract

There is a growing appreciation that the membrane physical properties are essential to cell and protein function. Simply altering the thickness of model membranes has been shown to influence the biological activity of several proteins, while incorporating peptides into lipid membranes also is known to affect the bilayer structural properties. Clearly there is a synergy in lipid-protein interactions in determining the membrane properties; however, the nature of these interactions are not well understood. Here we use a combination of small angle scattering techniques and neutron spin echo spectroscopy (NSE) to investigate the effects of incorporating a small peptide on both the structure and dynamics of model membrane systems. In particular, we investigated the effects of the antimicrobial peptides gramicidin and alamethecin on the lipid bilayer structure using small angle x-ray and neutron scattering. The structural studies were complemented by NSE experiments to probe the collective bending and thickness fluctuation dynamics in these model systems. Notably, the NSE results revealed enhanced thickness fluctuation dynamics in lipid bilayers containing low concentration of gramicidin that were dampened with increasing peptide concentration. An enhancement in dynamics was not seen in bilayers containing alamethicin, suggesting that the dynamics not only depend on peptide concentration, but also peptide orientation within the membrane