De Novo Design of Tryptophan Containing Broad-Spectrum Cationic Antimicrobial Octapeptides.

With the advent of antibiotic resistant organisms, development of alternate classes of molecules other than antibiotics to combat microbial infections, have become extremely important. In this context, antimicrobial peptides have taken center stage of antimicrobial therapeutic research. In this work, we have reported two cationic antimicrobial octapeptides WRL and LWRF, with broad spectrum antimicrobial activities against several strains of ESKAPE pathogens. Both the peptides were membrane associative and induced microbial cell death through membranolysis, being selective towards microbial membranes over mammalian membranes. The AMPs were unstructured in water, adopting partial helical conformation in the presence of microbial membrane mimics. Electrostatic interaction formed the primary basis of peptide-membrane interactions. WRL was more potent, salt tolerant and faster acting of the two AMPs, owing to the presence of two tryptophan residues against that of one in LWRF. Increased tryptophan number in WRL enhanced its membrane association ability, resulting in higher antimicrobial potency but lower selectivity. This experimental and computational work, established that an optimum number of tryptophan residues and their position was critical for obtaining high antimicrobial potency and selectivity simultaneously in the designed cationic AMPs. Understanding the peptide membrane interactions in atomistic details can lead to development of better antimicrobial therapeutics in future.