Antimicrobial Activity of Cationic Peptides Designed from Neutral Peptide

Antimicrobial peptides (PAMs) play an important role in the innate defense systems of most organisms; they act against bacteria, fungi, viruses and parasites. The mechanism of action of cationic PAMs rely on their capacity to interact with the anionic microbial membrane surface. The cecropin family was identified as one of the most important peptides in insects. Such peptides do not contain cysteine residues and are classified as a-helical. To study the effect of the charge on the peptide structure, we introduced positive charge residues in the last 18 residues at the N-end of cecropin-D (WT) and evaluated the biological activity of the modified peptides. Two analogous peptides from cecropin-D were obtained by synthesis of a solid phase (SSP) with charges of +5 and +9. The analogous peptides were generated as followed: peptide +5 with three substitutions (E6R, E8R and Q(12)K) and peptide +9 with five substitutions (E1R, E6R, E8R, Q(12)K, and D16K). Antibacterial activity was evaluated to investigate the effects of the positive charge in these two analogue peptides against two groups of bacteria. The cationic peptides showed higher antimicrobial activity against Gram-negative and Gram-positive bacteria than the WT peptide. The 3D representations of the peptides showed that they have a-helical structure. Our results demonstrate that changes in the charge of peptides increase the antibacterial activity.