Membrane interaction and antimicrobial features of two peptides diastereomers from Bombina skin

Bombinins H are mildly cationic antimicrobial peptides isolated from the skin of the anuran genus Bombina. Some members of this peptide family coexist in skin secretions as diastereomers in which a single L-amino acid is post-translational modified to produce the respective D-amino acid. We have evaluated the antimicrobial activity of H2 and H4 (the latter containing a D-alloisoleucine at the second N-terminal position) against a large panel of Gram-negative and Gram-positive bacteria; performed membrane permeation assays on both intact cells and model membranes mimicking the composition of the plasmamembrane of Gram-negative/positive bacteria; used biochemical tools to monitor the peptides’ ability to translocate through the membrane of liposomes mimicking Escherichia coli inner membrane. The results highlight that the presence of a single D-amino acid in the sequence of an antimicrobial peptide is decisive to determine its target microbial cell selectivity and its membrane perturbing activity.