1.C.114 The Membrane permeabilizing Peptide, Moricin (Moricin) Family

Moricin, showing antibacterial and antifungal activities, was isolated from the hemolymph of the silkworm, Bombyx mori. This basic peptide consists of 42 amino acids and is responsible for the antibacterial activity in B. mori against Gram-positive bacteria (Hara and Yamakawa 1995). A target of the peptide is the bacterial cytoplasmic membrane. The N-terminal portion of the peptide, containing a predicted alpha-helix, is responsible for an increase in the membrane permeability. 

Manduca sexta moricin, a 42-residue peptide of 4539 Da,  exhibited potent antimicrobial activities against a broad spectrum of Gram-positive and Gram-negative bacteria with a minimal inhibitory concentration of 1.4 μM. The mRNA levels of M. sexta moricin increased substantially in fat body and hemocytes after the larvae were challenged with bacterial cells. The solution structure of this AMP was determined by two-dimensional 1H-1H -nuclear magnetic resonance spectroscopy. The tertiary structure is composed of an eight-turn alpha-helix spanning almost the entire peptide (Dai et al. 2008).