Depuration of Cadmium from Blue Mussel (Mytilus edulis) by Protein Hydrolysate-Fe2+ Complex: The Role of Metallothionein

Metallothionein (MT) plays a major role in the detoxification of toxic metal ions in mussel. This study served to investigate the effects of prepared protein hydrolysate-Fe2+ (PH-Fe2+) on depuration of cadmium salt (Cd2+) from blue mussel (Mytilus edulis). The results indicated that Cd2+ concentrations in control ranged from 46.1 to 47.1 g/g during 15 d of depuration. While, 40 mg/L PH-Fe2+ feed mussels exhibited obvious changes in Cd2+ concentration variables, which decreased by 22.8 g/g after 15 d of depuration, making them significantly lower than the values of the control. Our assumption was that Cd2+ could be dissociated effectively from the complex of MT-Cd2+ in mussels affected by the incorporation of PH-Fe2+ during the feeding period. Further results of homology modeling and molecular dynamics (MD) confirmed that the combined power between MT and Cd2+ weakened significantly by PH-Fe2+. This condition affected the charge density and/or the loop flexibility of MT and decreased the interaction energy within MT-Cd2+ complex and resulted in the release of Cd2+ from the complex, thereby exhibiting excretion detoxification. Finally, by comparing the experimental results to MD results, significant positive correlations were observed between PH-Fe2+ and the depuration of Cd2+ from MT-Cd2+ complex. Overall, the findings of this study may help better understand the depuration mechanisms of Cd2+ combined with MT, and the PH-Fe2+ can be recommended as a depuration agent to decrease Cd2+ concentrations in mussels.