IMPROVEMENT OF OUTER MEMBRANE-PERMEABILIZING AND LIPOPOLYSACCHARIDE-BINDING ACTIVITIES OF AN ANTIMICROBIAL CATIONIC PEPTIDE BY C-TERMINAL MODIFICATION

Antimicrobial cationic peptides have been discovered in many different organisms and often possess a broad range of activity. In this study, we investigated the mechanisms of actions of melittin and two synthet ic peptides, CEME (a cecropin-melittin hybrid) and CEMA, against gram- negative bacteria. CEMA was produced by recombinant DNA procedures and is an analog of CEME with a modified C terminus resulting in two addi tional positive charges. All three peptides showed good antimicrobial activity against four different gram-negative bacteria, but only CEMA was able to somewhat augment the activity of some conventional antibio tics in synergy studies. Studies using the bacteria Pseudomonas aerugi nosa and Enterobacter cloacae showed that the peptides all possessed t he ability to permeabilize bacterial outer membranes to the hydrophobi c fluorophor 1-N-phenylnaphthylamine and the protein lysozyme, with CE MA being the most active. CEMA also had the strongest relative binding affinity for bacterial endotoxin (lipopolysaccharide). These data col lectively indicated that these peptides all cross the outer membrane b y the self-promoted uptake pathway and that CEMA is the peptide most e ffective at accessing this pathway.