Folded structure and insertion depth of the frog-skin antimicrobial peptide esculentin-1b(1−18) in the presence of differently charged membrane-mimicking micelles

Antimicrobial peptides (AMPs) are e!ectors of the innate immunity of most organisms. Their role in the defense against pathogen attack and their high selectivity for bacterial cells make them attractive for the development of a new class of antimicrobial drugs. The N-terminal fragment of the frog-skin peptide esculentin-1b (Esc(1−18)) has shown broad-spectrum antimicrobial activity. Similarly to most cationic AMPs, it is supposed to act by binding to and damaging the negatively charged plasma membrane of bacteria. Di!erently from many other AMPs, Esc(1−18) activity is preserved in biological "uids such as serum. In this work, a structural investigation was performed through NMR spectroscopy. The 3D structure was obtained in the presence of either zwitterionic or negatively charged micelles as membrane models for eukaryotic and prokaryotic membranes, respectively. Esc(1−18) showed a higher a#nity for and deeper insertion into the latter and adopted an amphipathic helical structure characterized by a kink at the residue G8. These $ndings were con$rmed by measuring penetration into lipid monolayers. The presence of negatively charged lipids in the bilayer appears to be necessary for Esc(1−18) to bind, to fold in the right threedimensional structure, and, ultimately, to exert its biological role as an AMP