A novel antibacterial peptide family isolated from the silkworm, Bombyx mori

Three structurally related and novel antibacterial peptides have been isolated from the haemolymph of the silkworm, Bombyx mori, immunized with Escherichia coli. These peptides were 32 amino acids long and characteristically rich in proline residues. A unique threonine residue in each peptide was O-glycosylated and the modification seemed to be important for expression of antibacterial activity. The primary structure and antibacterial character of the novel peptides resemble those of abaecin (41% identity in amino acid sequence), an antibacterial peptide of the honeybee, although abaecin is not O-glycosylated. Incubation of the novel peptides with a liposome preparation caused leakage of entrapped glucose under low-ionic-strength conditions, suggesting that a target of the peptides is the bacterial membrane. We propose the name ‘lebocin’ for the novel peptide family isolated from B. mori.