Moricin, a novel type of antibacterial peptide isolated from the silkworm, Bombyx mori

A novel antibacterial peptide that shows antibacterial activity against Staphylococcus aureus was isolated from the hemolymph of the silkworm, Bombyx mori. The novel peptide consisted of 42 amino acids and was highly basic. This peptide indicated no significant similarity with other antibacterial peptides. The peptide showed antibacterial activity against several Gram-negative and -positive bacteria and had a higher activity against Gram-positive bacteria than cecropin B1, a major antibacterial peptide of B. mori. The novel peptide was inducible by bacterial injection. These results suggest that the peptide is responsible for the antibacterial activity in B. mori against Gram-positive bacteria. The effects of the peptide on bacterial and liposomal membranes showed that a target of the peptide is the bacterial cytoplasmic membrane. The results also suggest that the N-terminal portion of the peptide, containing a predicted alpha-helix, is responsible for an increase in the membrane permeability. We propose the name "moricin" for this novel antibacterial peptide isolated from B. mori.