In vitro and in silico studies of the membrane interactions of mollusk-derived antimicrobial peptides Pom-1 and Pom-2.

Pom-1 and Pom-2 are antimicrobial peptides natively produced by the fresh-water snail Pomacea poeyana. They selectively kill bacteria and yeasts, but present no cytotoxic effects for mammalian cells, and their mode of action is still unclear. Liposome calcein leakage experiments were used to measure permeability effects of both peptides, while Laurdan generalized polarization (GP) was used to determine the effect of the AMPs on apparent membrane fluidity. Only Pom-1 induced dye leakage, with the greatest activity in the bacterial model, following modest activity in the fungal model, and no activity towards the mammalian membrane. Likewise, the greatest effect on membrane fluidity induced by Pom-1 was observed in the bacterial model, with slight changes registered with the fungal model. The effect of the peptide was dosis-dependent. The intrinsic tryptophan fluorescence spectroscopy of Pom-1 indicated that, at a minimum, the hydrophobic N-terminal end of the peptide inserted into all three membranes. Molecular dynamics simulations corroborated the in vitro observations, as Pom-2 did not interact with or perturb membrane properties. Although Pom-1 showed greater free binging energy with the bacterial model, it inserted to a greater depth into the fungal membrane, but without significantly modifying membrane properties. The different capabilities of Pom-1 and Pom-2 to interact with the different bilayers were mainly due to biochemical properties of the peptides such as net charge a neutral pH, hydrophobicity, Bowman index, among others. Pom-1´s secondary structure was stable throughout the simulations, while Pom-2 tended to denature over time. The in-silico analyses suggested that peptide aggregation negatively impacted membrane peptide interaction and subsequent insertion. Conclusively, we present strong evidence that the plasma membrane is the molecular target of Pom-1; The Pom-2 target remains unknown.