Cysteine contributions to metal binding preference for Zn/Cd in the beta-domain of metallothionein.

Previous studies showed that metals in the beta-domain of metallothionein (MT) are more readily exchangeable and the level of avidity is site specific. This is reflected by energy differences computed with a series of simulated structures derived from X-ray crystallography. In this study, we examined further the contribution of each of the nine cysteines in the beta-domain. By semi-empirical MNDO calculations, we observed that the relative average binding strength is the strongest for Cys21 to Cd[M4] and for Cys26 to Zn[M3], except for the bridging cysteines. These results suggest that binding site preference for Zn/Cd is determined by binding strength between specific cysteines and metal ion species.