RESUMEN
Among the potential novel therapeutics to treat bacterial infections, antimicrobial peptides (AMPs) are a very promising substitute due to their broad-spectrum activity and rapid bactericidal action. AMPs strongly interact with the bacterial membrane, and the need to have a correct understanding of the interaction between AMPs and lipid bilayers at a molecular level prompted a wealth of experimental and theoretical studies exploiting a variety of AMPs. Here, we studied the effects of magainin H2 (Mag H2), an analog of the well-known magainin 2 (wt Mag 2) AMP endowed with a higher degree of hydrophobicity, on giant unilamellar vesicles (GUVs) concentrating on its permeabilization activity and the effect on the lipid bilayer mechanical properties. We demonstrated that the increased hydrophobicity of Mag H2 affects its selectivity conferring a strong permeabilization activity also on zwitterionic lipid bilayers. Moreover, when lipid mixtures including PG lipids are considered, PG has a protective effect, at variance from wt Mag 2, suggesting that for Mag H2 the monolayer curvature could prevail over the peptide-membrane electrostatic interaction. We then mechanically characterized GUVs by measuring the effect of Mag H2 on the bending constant of lipid bilayers by flickering spectroscopy and, by using micropipette aspiration technique, we followed the steps leading to vesicle permeabilization. We found that Mag H2, notwithstanding its enhanced hydrophobicity, has a pore formation mechanism compatible with the toroidal pore model similar to that of wt Mag 2.
RESUMEN
Given the increasing trend in bacterial antibiotic resistance, research on antimicrobial peptides and their mechanisms of action has become of huge relevance in the last years. Several studies have investigated the effects of a large variety of antimicrobial peptides directly on bacteria or on model lipid bilayers. In the case of model lipid bilayers, different systems are typically exploited; however, different results could be obtained due to the specific properties of the used system. Supported Lipid Bilayers and Giant Unilamellar Vesicles are among the most popular model systems. Here we used Atomic Force Microscopy and fluorescence microscopy to study the interaction of the antimicrobial peptide Magainin H2, an analog of Magainin 2 with increased hydrophobicity, on Supported Lipid Bilayers. We found that, for this kind of model bilayer, due to its strong interaction with the support, the lateral expansion of the membrane induced by the interaction with the peptides is initially inhibited and subsequently proceeds creating new bilayer regions with many defects. This scenario gives rise in Supported Lipid Bilayers to effects like initial increase of lateral pressure, formation of lipid tubes to release this increase, or development of bilayer regions with lower lipid density. Our results highlight that care should be given to the selected model system when studying and comparing the interaction of peptides with other lipid bilayer model systems.