Design of novel antimicrobial peptides based on structure-antibiotic activity relationships of Cecropin A, Magainin 2 and Melittin

In order to investigate structure-antibiotic activity relationships of cecropin A (CA)-magainin 2 (MA) and cecropin A (CA)-melittin (ME) hybrids, its analogues with amino acid substitutions were designed and synthesized. The increase in hydrophobicity or α-helicity of the peptides was correlated with an increase in hemolytic activity rather than antimicrobial activity. The membrane disrupting properties of CA-MA hybrids, measured by the induced release of vesicle-entrapped calcein, were found to have remarkable discrepancies according to the amphipathic nature of each peptide. The tryptophan flourescence spectra showed that upon interaction with the phospholipid vesicle, the peptide acquired the ordered structure and α-helical conformation by moving a tryptophan residue into the nonpolar environment of the phospholipid vesicle. Antifungal peptide (K^18,19-CA-ME) acts by the pore or ion channel formation on cell membranes of T. beigelii were confirmed using the fluorescence activated flow cytometric analysis and confocal laser scanning microscopy.