Antimicrobial peptides not only represent an important component of innate host defense against microbial colonization and a link between innate and adaptive immunity,but also form a foundation for the development of new therapeutic agents.As the most important antimicrobial peptide families in mussel,mytilin and myticin contain many members referred to as isofoms and have the highest abundance in mussel serum,which means these two families play a key role in mussel innate immunity.To investigate the molecular diversity and the sequence characterization of mytilin and myticin from Mytilus coruscus,the cDNA of mytilin and myticin were cloned respectively by PCR method using M.coruscus hemocyte cDNA library as template.Eight deferent mytilin cDNAs and nine deferent myticin cDNAs were cloned from M.coruscus hemocyte cDNA library,respectively.The precursor translated from mytilin cDNA contains a putative signal peptide of 22 residues,a processing peptide sequence of 34 amino acids,and a C-terminal extension of 46 residues rich in acidic residues; while the precursor translated from myticin cDNA contains a putative signal peptide of 20 residues,a processing peptide sequence of 40 amino acids,and a C-terminal extension of 37 residues.Both mytilin and myticin of M.coruscus are characterized by abundant cationic amino acids and eight cysteins which formed four disulfides.Sequence analysis of the coding frame showed that the variation loci of these two kinds of antimicrobial peptide mainly occurred on mature peptide region,which might result from direct interaction of these peptides with the surrounding pathogens in the changing environment and thus become a likely cause of molecular adaptation of certain amino acid sites in mytilin and myticin variants.This study laid the foundation for intensive study on immune mechanisms as well as screening antimicrobial peptide molecules from M.coruscu antimicrobial peptides.