A MEMBER OF THE ARTHROPOD DEFENSIN FAMILY FROM EDIBLE MEDITERRANEAN MUSSELS (MYTILUS-GALLOPROVINCIALIS)

Plasma from the mussel Mytilus galloprovincialis previously immunized by injecting them with bacteria contains several bactericidal proteins . One protein, MGD-1, was purified by reverse-phase HPLC of supernatan t from acidified cell-free hemolymph. Its biological activity is direc ted against both gram-positive and gram-negative bacteria but it is no t cytotoxic towards human erythrocytes nor protozoa. As determined by mass spectrometry, the molecular mass of MGD-1 is 4418 Da. Primary-str ucture analysis revealed 38 amino acids including 8 cysteines and a mo dified amino acid residue in position 28. Computer searches unambiguou sly recognized the signature of an arthropod defensin, but the presenc e of two extra cysteines and of one modified amino acid suggest that i t is a previously unknown member of that family.