OBJECTIVES: To investigate the immune defense of the annelid Nereis diversicolor and the key role of a oxygen-binding protein, the metalloprotein MPII animals were subjected to bacteria infection.
METHODS AND RESULTS: Using RACE-PCR, we have cloned the complete cDNA coding for the MPII related to the hemerythrin family in the sand worm Hediste diversicolor. This cDNA (883 pb) codes for a polypeptide of 119 amino acid residues with no signal peptide. Previous works have identified this protein as a cadmium scavenger. We here clearly demonstrated that this protein is also involved in the worm defence towards bacteria growth by its iron scavenger ability. This protein is expressed and produced in a haematopoietic center that floats freely in the coelomic fluid before stored in a particular hemocyte type: the granulocyte type 1. During bacterial challenge, this protein contained in these cells is discharged into the blood stream 3-4 hours after the infection and remains active for approximately 10 hours. This time period blocks progression of the pathogen and its attachment to tissues.
CONCLUSION: These results reflect that MPII in conjunction with others partners like lysozyme act as defence molecule for the sand worm.