Identification and isolation of the bactericidal domains in the proteinase inhibitor aprotinin.

Aprotinin is a protein proteinase inhibitor of 58 amino acids, located in bovine mast cells which also possesses antibacterial activity. Digestion of aprotinin by clostripain yielded three antimicrobial oligopeptide fragments with the sequences RPDFCLEPPYTGPCK (residues 1-15), IIRYFYNAKAGLCQTFVYGGCR (residues 18-39) and AKRNNFKSAEDCMRTCGGA (residues 40-58). With the exception of residues 16 (alanyl) and 17 (arginyl) they cover the whole aprotinin structure. The three oligopeptides were synthesized and found to exert a broad spectrum of antimicrobial activities. Most potent was oligopeptide IIRYFYNAKAGLCQTFVYGGCR which at a concentration of 7 x 10(-9) M exhibited a high bactericidal activity against the eleven gram-positive and gram-negative bacterial strains tested. None of the purified oligopeptides showed any antiproteolytic activity. Our results suggest that aprotinin has multiple antimicrobial domains which are independent of the antiproteolytic function of the original molecule.