title: Semi-empirical simulation of Zn/Cd binding site preference in the metal binding domains of mammalian metallothionein.
abstract: Metallothionein, a two-domain protein, naturally binds seven gram atoms of divalent ions such as Zn and Cd. Four of the metals (M1, M5, M6 and M7) are found in the alpha-domain and three (M2, M3 and M4) in the beta-domain. Previous studies have shown that metals in the beta-domain are more readily exchangeable, and the level of avidity is site specific. By semi-empirical MNDO modified neglect of diatomic overlap calculations, we found the tendency of binding energy for Cd to be M4 > M2 > M3 [corrected] in the beta-cluster and M5 > M7 > M1, M6 in the alpha-cluster. Thus, the replacement of Zn by Cd can be expected to follow the order M4-->M2-->M3 in the beta-domain and M5-->M7-->M1 or M6 in the alpha-domain. This is reflected by energy differences computed with a series of simulated structures derived from either X-ray crystallography or NMR coordinates.
authors.affiliation: Department of Life Sciences, National Tsing Hua University, Hsing-Chu, Taiwan, Republic of China.
authors.forename: C C
authors.initials: CC
authors.lastname: Chang
authors.forename: P C
authors.initials: PC
authors.lastname: Huang
mesh_terms: D000818:Animals; D001665:Binding Sites; D002104:Cadmium / Q000737:chemistry*; D003198:Computer Simulation; D003545:Cysteine / Q000737:chemistry; D008668:Metallothionein / Q000737:chemistry*; D008958:Models, Molecular; D009068:Movement; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*
chemical_list: D002104:Cadmium; D008668:Metallothionein; D015032:Zinc; D003545:Cysteine