Study of the effect of the antibacterial peptide P8.1 (synthesized “de novo”) on anionic vesicles using spectroscopic techniques

Abstract

Since bacteria have developed an alarming rate of resistance to antibiotics in recent decades, new therapeutic alternatives are continually sought, among which antimicrobial peptides (AMPs) stand out. These peptides has great potential for clinical use due to their multiple mechanisms of action and broad spectrum of activity. The aim of this work was to study the effect of the cationic AMP P8.1 synthesized “de novo”, which previously showed antimicrobial activity, on liposomes of DLPG and DPPG (liquid-crystalline phase and gel phase at room temperature, respectively) using spectroscopic techniques. We evaluated the effect of P8.1 on vesicles of both lipids (16:1 lipid:peptide ratio), upon one hour of interaction, using Zeta Potential (ZP), Florescence and Raman Spectroscopy. ZP experiments showed that P8.1 was capable of interacting with both anionic liposomes. The increase in surface charge due to the addition of P8.1 was practically immediate in DPPG liposomes and it was a little slower in DLPG vesicles. Raman spectra were obtained at room temperature for DLPG or DPPG liposomes with and without peptide. It was observed that P8.1 decreased the signals corresponding to the phosphate group in both systems, in a good agreement with the increase of ZP. On the other hand, a greater packing of lipids was derived from the spectra of the DLPG/P8.1 system, while the opposite was observed in DPPG/P8.1. The same behavior was observed by using generalized polarization obtained by Fluorescence spectroscopy using Laurdan. Therefore, it was confirmed that P8.1 is able to decreasing the order in DPPG liposomes and increasing it in DLPG liposomes. These results allow us to conclude that in the first instance AMP P8.1 binds to both types of lipids through the interaction of positive charges of the peptide with the phosphate group of the lipids and, then, produces changes in the fluidity of the membrane depending on the degree of insertion of the peptide into the core of the bilayer.