Mode of action of the antimicrobial peptide Bombinin H2 and its natural single D-amino acid diastereomer, on Leishmania parasites and model membranes

Leishmaniasis encompasses a wide range of infections caused by the human parasitic protozoan species belonging to the Leishmania genus. It appears frequently as an opportunistic disease, especially in virus-infected immunodepressed people. Similarly to other pathogens, parasites became resistant to most of first-line drugs. Therefore, there is an urgent need to develop antiparasitic agents with new modes of action. Gene-encoded antimicrobial peptides (AMPs) are promising candidates. They are lethal for a broad spectrum of pathogens, but little is known about their activity and mode of action against the insect (promastigote) and the mammalian (amastigote) stage of the Leishmania parasite. We report on the lethal activity of bombinin H2 and H4, two AMPs isolated from the skin secretions of Bombina variegata, which differ one from each other by only the configuration of a single amino acid. We found that H4, which represents the first natural AMP of animal origin containing a D-amino acid in its sequence, is the most active one. The mode of action of the peptides on Leishmania and model membranes was investigated. These studies include: membrane depolarizition, membrane leakage and damage, membrane binding (using surface plasmon resonance) and the determination of the structure and organization of the peptide in Leishmania mimicking membranes (using ATR-FTIR spectroscopy). Our results highlight the importance of a single a-amino acid epimerization as a tool used by nature to modulate the activity of AMPs. In addition, our findings suggest bombinins H as potential templates for the design of new drugs with a new mode of action against Leishmania.