DE-NOVO ANTIMICROBIAL PEPTIDES WITH LOW MAMMALIAN-CELL TOXICITY

De novo antimicrobial peptides with the sequences: (KLAKKLA)(n), (KLAK LAK)(n) (where n = 1, 2, 3), (KALKALK)(3), (KLGKKLG)(n), and (KAAKKAA) (n) (where n = 2, 3), were prepared as the C-terminus amides. These pe ptides were designed to be perfectly amphipathic in helical conformati ons. Peptide antibacterial activity was tested against Escherichia col i, Pseudomonas aeruginosa, and Staphylococcus aureus. Peptide cytotoxi city was tested against human erythrocytes and 3T3 mouse fibroblasts. The 3T3 cell testing was a much more sensitive test of cytotoxicity. T he peptides were much less lytic toward human erythrocytes than 3T3 ce lls. Peptide secondary structure in aqueous solution, sodium dodecylsu lfate micelles, and phospholipid vesicles was estimated using circular dichroism spectroscopy. The leucine/alanine-containing 21-mers were b acteriostatic at 3-8 mu M and cytotoxic to 3T3 cells at about 10 mu M concentrations. The leucine/alanine- or leucine/glycine-containing 14- mers and the leucine/glycine 21-mer were bacteriostatic at 6-22 mu M b ut had much lower cytotoxicity toward 3T3 cells and higher selectiviti es than the natural antimicrobial peptides magainin 2 amide and cecrop in B amide. The 7-mer peptides are devoid of biological activity and o f secondary structure in membrane mimetic environments. The 14-mer pep tides and the glycine-containing 21-mer show modest levels of helicity in model membranes. The leucine/alanine-containing 21-mer peptides ha ve substantial helicity in model membranes. The propensity to alpha-he lical conformation of the peptides in amphipathic media is proportiona l to their 3T3 cell cytotoxicity.