Dissociation of antibacterial and hemolytic activities of an amphipathic peptide antibiotic.

Using an alanine-scanning method, we have found that the antibacterial and hemolytic activities of the amphipathic cyclic decapeptide antibiotic tyrocidine A depend on different structural components. Single substitution of glutamine-6 of the natural product with a cationic amino acid results in a therapeutic index enhancement of up to 140-fold. Successful dissociation of the two intimately associated properties should enable discovery of novel analogues with both high bacterial selectivity and antibacterial potency to counter microbial resistance.