Purification and characterization of a proline-rich antibacterial peptide, with sequence similarity to bactenecin-7, from the haemocytes of the shore crab, Carcinus maenas

Antibacterial peptides are important for non-specific host defence in many animals. They have been extensively characterized from mammals, amphibians, insects and chelicerates but have not so far been found in crustaceans. Here we report the presence of several constitutive antibacterial proteins, active against both gram-positive and gram-negative bacteria, in the haemocytes of the shore crab, Carcinus maenas. These proteins have molecular masses of >70 kDa, approximate to 45 kDa, approximate to 14 kDa and 6.5 kDa. The 6.5-kDa peptide has been purified to homogeneity by Sep Pak C-18 extraction, gel filtration and reverse-phase HPLC. Partial N-terminal sequence analysis further shows that it is proline rich and shares more than 60% identity in a 28-amino-acid overlap with the mature form of bactenecin 7, an antimicrobial peptide from bovine neutrophils which belongs to the cathelicidin family of mammalian peptide antibiotics.