Interactions of antimicrobial peptides with bacterial membrane model systems and with whole E. coli bacterial cells

Antimicrobial peptides are a primitive component of the innate immune system, produced by organisms after the invasion of pathogens. Extensive studies have led to the discovery of a wide variety of such peptides, from diverse organisms, showing different activities and structures. Studies on peptides secreted on the frog skin allowed the characterization of a class of short peptides, temporins, characterized by strong antimicrobial activity against Gram-positive bacteria and fungi. We have recently developed a Temporin B analogue, named TB_G6AKK, composed of natural amino acids, showing activity at low concentrations either against Gram-positive and Gram-negative bacteria (Avitabile et al 2013, in press). TB_G6AKK interacts with E.coli LPS, as demonstrated by fluorescence, CD and ITC studies, and folds as a kinked helix upon interaction with the E.coli LPS, as demonstrated by NMR. Studies aimed to characterize the ability of this peptide to kill pathogens as Pseudomonas aeruginosa, whose infection is cause of complications in patients suffering cystic fibrosis are currently in progress. In order to deeply characterize the interactions of such peptide with the bacterial cells, as LPS is only one of the components of the bacterial cell wall, we started to explore the secondary structure of the peptide in the presence of whole bacterial cells by CD and by fluorescence the binding of the peptide to the cells. Analysis of the data obtained with cells and comparison with those obtained with LPS will help us to understand the effectiveness of the LPS as a model system to represent the cells Gram negative bacteria.