The impact of membrane lipid composition on antimicrobial function of an α-helical peptide

VP1, a putative α-helical antimicrobial peptide (α-AMP) inhibited growth of Bacillus subtilis and Escherichia coli at 500 μM. The peptide induced stable surface pressure changes in monolayers formed from B. subtilis native lipid extract (circa 4.5 mN m−1) but transient pressure changes in corresponding E. coli monolayers (circa 1.0 mN m−1), which led to monolayer disintegration. Synthetic lipid monolayers mimetic of the extracts were used to generate compression isotherms. Thermodynamic analysis of B. subtilis isotherms indicated membrane stabilisation by VP1 (ΔGMix < 0), via a mechanism dependent upon the phosphatidylglycerol to cardiolipin ratio. Corresponding analysis of E. coli isotherms indicated membrane destabilisation by the peptide (ΔGMix > 0). Destabilisation correlated with PE levels present and appeared to involve a mechanism resembling those used by tilted peptides. These data emphasise that structure/function analysis of α-AMPs must consider not only their structural characteristics but also the lipid make-up of the target microbial membrane.