Mode of action of sapecin, a novel antibacterial protein of Sarcophaga peregrina (flesh fly).

Sapecin is an antibacterial protein purified from the culture medium of NIH-Sape-4, an embryonic cell line of Sarcophaga peregrina [Matsuyama, K. & Natori, S. (1988) J. Biol. Chem. 236, 17112-17116]. As this protein inhibited the growth of Gram-positive bacteria better than that of Gram-negative bacteria, we studied its mode of action with special reference to its effects on S. aureus and Escherichia coli. Results showed that sapecin had high affinity for cardiolipin, which is a major phospholipid of S. aureus. Moreover, a mutant of E. coli with a defect in cardiolipin synthesis was more resistant to sapecin than wild type E. coli, suggesting that cardiolipin is a target for sapecin. Lipopolysaccharide of E. coli was also found to be a barrier for the antibacterial activity of sapecin.