X-ray reflectivity study of structural modifications to supported phospholipid bilayers due to interactions with the antimicrobial peptide, indolicidin

Antimicrobial peptides (AMPS) are short peptide sequences (10-30 residues) which can destroy microbes by disrupting the cell membrane. Indolicidin, a 13 residue, cationic peptide, was one of the first AMPS to be isolated and has been studied by a number of research groups. However, the molecular mechanism for the antimicrobial properties of Indolicidin is still not fully understood. In order to investigate the details of the membrane-peptide interaction, we have fabricated biometric phospholipid membranes supported on atomically flat silicon substrates and characterized their structure using x-ray reflectivity in the presence and absence of Indolicidin. Membrane thickness and roughness were characterized as a function of the molar fraction of indolicidin. We observe a slight decrease in membrane thickness and a reduction in overall bilayer contrast as the amount of Indolicidin increases which is consistent with the recent work of Nielson et. al. ³