Purification and characterization of an antimicrobial peptide mytichitin-chitin binding domain from the hard-shelled mussel, Mytilus coruscus

An antimicrobial peptide with 55 amino acid residues was purified by C-18 reversed-phase high-performance liquid chromatography (HPLC) from foot extract of the hard-shelled mussel, Mytilus coruscus. This peptide showed strong antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as fungi. The purified peptide was determined to have a molecular mass of 6202 Da by matrix-assisted laser desorption/ionization time-of-flight mass spectrophotometry (MALDI-TOF/MS). The identified 20-amino acid sequence of the purified peak by Edman degradation shared 100% identity with the N-terminal regions of mytichitin-1, mytichitin-2, mytichitin-3, mytichitin-4, mytichitin-5, and chitinase-like protein-1, and so was named mytichitin-CBD. The cDNA of mytichitin-CBD was cloned and sequenced by rapid amplification of cDNA ends (RACE). The mRNA transcripts were mainly detected in foot tissue, and they were up-regulated and peaked at 4 h after bacterial infection. We constructed and expressed recombinant mytichitin-CBD protein which displayed antimicrobial activity against Gram-negative bacteria Gram-positive bacteria and the fungus as well as anti-parasitic activity against scuticociliates. The results of this study demonstrate that the peptide isolated from M. coruscus is related to the innate immune system of this marine invertebrate and is a possible alternative to antibiotics.