Structure-Activity Relationships of Peptide Antibiotics with Improved Bacterial Cell Selectivity of Pseudin

Pseudin is a naturally occurring 24 amino-acid-residue antimicrobial peptide derived from the skin of paradoxical frog Pseud’s paradoxa . It shows potency against the bacteria and antibiotic-resistant bacteria strain, but has high cytotoxicity against mammalian cell. In our previous study, substitution of Pro 11 for Gly (Ps-P) increased bacterial cell selectivity but decreased the antibacterial activity of pseudin. In this study, we designed pseudin analogue, Ps-4K-P with increased cationicity up to +7 in Ps-P by substituting Glu14, Gln10, Gln24, and Leu18 with Lys. Ps-4K-P showed improved potent antibacterial activity with high bacterial cell selectivity. We determined the tertiary structure of Ps-4K-P in the presence of DPC micelles by NMR spectroscopy and it has a hinge structure at Pro 11 followed by three turn helices from Pro 11 to Val 23 at the C-terminus. Amphipathicity with increased cationicity as well as helix-hinge-helix structural motif provided by introduction of a Pro at position Gly 11 are the crucial factors which confer antibacterial activity with bacterial cell selectivity to Ps-4K-P.