Interaction of an antimicrobial peptide with a model lipid bilayer using molecular dynamics simulation.

We present results of molecular dynamics simulations of the interaction of a positively charged antimicrobial peptide, carnobacteriocin B2, with a mixed (anionic-zwitterionic) lipid bilayer carrying a net negative charge. When the peptide is initially immersed in an aqueous medium, it approaches the bilayer surface because of electrostatic attraction. Insertion of the single peptide in the bilayer, however, is not spontaneous. Simulations are also conducted by employing initial configurations where the peptide is partially or completely inserted into the bilayer. When the peptide is partially inserted into the bilayer, it experiences a slight loss of helical structure with the appearance of a hinge region in the C-terminal helix. Complete insertion of the peptide in the bilayer results in a stable straight helix with the N- and C-terminals electrostatically tethered to the opposing headgroups of the bilayer. The charged amino acids of the peptide do not cross the charged headgroups of the bilayer in any of the simulations, nor is any bilayer disruption observed in these studies. These results show that single peptides do not spontaneously penetrate lipid membranes and corroborate deductions from previous experimental studies that alternate mechanisms are necessary for their penetration into lipid bilayers.