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 sitespecific. This is reflected by energy differences computed with a series ofsimulated structures derived from X-ray crystallography. In this study, weexamined further the contribution of each of the nine cysteines in thebeta-domain. By semi-empirical MNDO calculations, we observed that therelative average binding strength is the strongest for Cys21 to Cd[M4] andfor Cys26 to Zn[M3], except for the bridging cysteines. These resultssuggest that binding site preference for Zn/Cd is determined by bindingstrength between specific cysteines and metal ion species.