Synthesis and Application of Small Cationic Peptides as Potential Antibiotics

Small cationic peptides have been recently found to have potential use as antibiotics. Wenzel et al tested the effectiveness of a peptide consisting of arginine and tryptophan repeats, RWRWRW‐NH2, with a terminal amine group. The arginine and tryptophan residues were chosen because of their highly reactive nature and for the size of the side chain. They found that the peptide would embed itself in the cell wall of a bacterium. The objective of this project is to expand upon the work done by Wenzel et al. Peptide synthesis is being accomplished via the Merrifield Synthesis method. This method utilizes a resin bead with the first amino acid attached to it; through a series of additions and washes the peptide is synthesized in one reaction vessel. Following synthesis, the peptide is cleaved from the bead and eluted from the vessel. The peptide synthesized by Wenzel is being used as a control and seven other scrambled peptides are being used as test groups. Three of the peptides consist of arginine and tryptophan, with the sequences being, RWWRWW‐NH2, RRWRRW‐NH2, and RRRWWW‐NH2. The other four peptides consist of lysine and tryptophan, with the sequences being, KWKWKW‐NH2, KWWKWW‐NH2, KKWKKW‐NH2, and KKKWWW‐NH2. The peptides being synthesized vary in the order of amino acids. We are interested to observe the effect the conformation of the peptide has on the effectiveness as an antibiotic. Moreover, lysine is substituted for arginine in order to determine if one amino acid is more effective than others. Once synthesized, the peptides are being introduced to lawns of eight species of gram positive bacteria in order to test effectiveness as an antibiotic. The mechanism of interaction is unknown for gram negative bacterial cell walls, and our laboratory does not have the capabilities to determine this.