Identification and characterization of an antibacterial peptide of the 26-kDa protease of Sarcophaga peregrina with antibacterial activity

Previously, we purified a serine protease with a molecular mass of 26 kDa t hat exhibits potent antibacterial activity from a pupal extract of Sarcopha ga peregrina (flesh fly). We divided this protease into 12 peptides and exa mined their antibacterial activity. A peptide corresponding to residues 155 to 174 (peptide 9) was found to exhibit antibacterial activity comparable to that of the 26-kDa protease. When Escherichia coli was treated with pept ide 9, the permeability of both the outer and inner membranes increased, an d substrates for beta -lactamase and beta -galactosidase entered the cells, but beta -galactosidase did not leak out of the cells under these conditio ns. It was suggested that residues 6 to 18 of peptide 9 form an amphiphilic a-helix under hydrophobic conditions with an N-terminal basic loop and the n interact with acidic phospholipids in the bacterial membranes.