Antimicrobial peptides are toxins that either (a) disrupt the integrity of cellular membranes or (b) instigate their own passage through these membranes on their way to intracellular targets. However, the mechanisms by which these peptides interact with a lipid bilayer (the defining component of a cell membrane) are poorly understood. Furthermore, given that a characteristic of lipid bilayers is to prevent the permeation of charged solutes, it remains puzzling why antimicrobial peptides are largely ionic.
In our letter, we use massively repeated computer simulations to quantify the favorable insertion of the antimicrobial peptide indolicidin into a lipid bilayer. The simulations suggest that a single molecule of indolicidin is capable of thinning and permeabilizing the lipid bilayer. The balance of hydrophobicity, charge, and structural disorder in this antimicrobial peptide appears to be well-suited to disrupt cell membranes, even in the absence of peptide aggregation or the formation of an ordered structure. Moreover, we emphasize the necessity of lengthy and massively repeated simulations to attain and gauge convergence of the calculations.
The image shows a simulation snapshot in which monomeric, intrinsically disordered indolicidin (yellow) resides in the bilayer’s hydrophobic core (white) and interacts with zwitterionic headgroups (brown) in both leaflets, drawing them inward and deforming the bilayer, causing the influx of water (cyan). Water and lipid in the foreground have been omitted for clarity.
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