Small molecules enhance the potency of natural antimicrobial peptides

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Abstract
The skin-associated microbiome plays an important role in general well-being and in a variety of treatable conditions. In this regard, endogenous antimicrobial peptides have a role in controlling the microbial population. We demonstrate here that certain small molecular species can amplify the potency of naturally-occurring antimicrobial peptides. For example, Niacinamide is a vitamin B3 analogue naturally found in foods and widely used in topical skin care products, and here we have investigated its cooperativity with the human antimicrobial peptide LL37 on the bacterium Staphylococcus aureus. We have also studied two other structurally related B3 analogs. We observed a clear synergistic effect of niacinamide and, to some extent, methyl niacinamide, whereas isonicotinamide showed no significant cooperativity with LL37. Adaptively-biased molecular dynamics simulations revealed that the analogs partition into the head group region of an anionic bilayer used to mimic the bacterial membrane. The observed effects on the physical properties of the membrane are well correlated with experimental activity. In contrast, the analogs have little effect on zwitterionic bilayers which mimic a mammalian membrane. We conclude that these vitamin B3 analogues can potentiate the activity of host peptides by modulating the physical properties of the bacterial membrane, and to a lesser extent through direct interactions with the peptide. The level of cooperativity is strongly dependent on the detailed chemistry of the additive, suggesting an opportunity to fine-tune the behaviour of host peptides.
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