Nanomechanical Characterization Of The Synergism Of Antimicrobial Peptides Pgla And Mag2 For Lipid Membrane Disruption

Antimicrobial peptides (AMPs) are amphiphilic molecules used by eukaryotic organisms as first defensive mechanism against infections. There is an increasing interest in the study of these peptides, considered promising alternatives to antibiotics for the treatment of multi-resistance pathogens. AMPs target the bacterial membrane leading to membrane lysis by pore formation and bilayer disruption. Here we studied PGLa and Magainin 2 (Mag2), which are known for a particular synergistic behavior in their antimicrobial activity. Although the molecular mechanism is not completely deciphered yet, lipid-mediated interactions are responsible for such synergism, directly correlated to a change in the peptide orientation into the membrane when both peptides are present. By means of atomic force microscopy (AFM), we investigated the effect of both individual peptides compared with their equimolar mixture on the structure, dynamics and nanomechanical properties of model lipid bilayers mimicking gram-negative bacterial cell membrane. Both individual peptides and the mixture led to a lateral expansion and a drastic thinning of the lipid bilayer, pointing out a deep structural reorganization of the membrane. AFM-based Quantitative nanomechanical mapping allowed us to investigate the membrane elastic constants and the resistance to failure. The mechanical rupture of the lipid bilayer by the AFM tip has been used extensively as a hallmark of its mechanical stability, usually by measuring the forces required to break the bilayer probed at different velocities. Interestingly, the elasticity of the membrane does not undergo significant changes upon the addition of the peptides. However, we observed a major increase in the breakthrough force, especially in the equimolar mixture of peptides. This particular nanomechanical behavior may indicate a complex synergistic mechanism between PGla and Mag2 to drive membrane disruption.