Role of molecular architecture on the relative efficacy of aurein 2.5 and modelin 5

In order to gain an insight into the mechanism of antimicrobial peptide action, aurein 2.5 and modelin-5 were studied. When tested against Staphylococcus aureus, aurein 2.5 showed approximately 5-fold greater efficacy even though the higher net positive charge and higher helix stability shown by modelin-5 would have predicated modelin-5 to be the more effective antimicrobial. However, in the presence of S. aureus membrane mimics, aurein 2.5 showed greater helical content (75% helical) relative to modelin-5 (51% helical) indicative of increase in membrane association. This was supported by monolayer data showing that aurein 2.5 (6.6 mN m− 1) generated greater pressure changes than modelin-5 (5.3 mN m− 1). Peptide monolayers indicted that modelin-5 formed a helix horizontal to the plane of an asymmetric interface which would be supported by the even distribution of charge and hydrophobicity along the helical long axis and facilitate lysis by non-specific membrane binding. In contrast, a groove structure observed on the surface of aurein 2.5 was predicted to be the cause of enhanced lipid binding (Kd = 75 μM) relative to modelin-5 (Kd = 118 μM) and the balance of hydrophobicity along the aurein 2.5 long axis supported deep penetration into the membrane in a tilt formation. This oblique orientation generates greater lytic efficacy in high anionic lipid (71%) compared to modelin-5 (32%)

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). 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. © 2007 Elsevier Ireland Ltd. All rights reserve