title: Crystal structure of Cd,Zn metallothionein.
abstract: The crystal structure of Cd,Zn metallothionein isoform II from rat liver has been determined using the anomalous scattering data from five Cd in the native protein. The structure of a 4Cd cluster was solved by direct methods. A 2.3 A resolution electron density map was calculated by an iterative solvent leveling and map inversion procedure. The structure is folded into two domains. The N-terminal domain (beta) of residues 1-29 enfolds a three-metal cluster of 1 Cd and 2 Zn coordinated by six terminal cysteine thiolate ligands and three bridging cysteine thiolates. The C-terminal domain (alpha) of residues 30-61 enfolds a 4Cd cluster coordinated by six terminal and five bridging cysteine thiolates. All seven metal sites have tetrahedral coordination geometry. The domains are roughly spherical, diameter 15-20 A; there is limited contact between domains. The folding of alpha and beta is topologically similar but with opposite chirality. Redundant, short cysteine-containing sequences have similar roles in cluster formation in both alpha and beta. The Cd1Zn2(cys)9 cluster is homologous with a 12 atom fragment of the Cd4(cys)11 cluster.
mesh_terms: D000818:Animals; D002104:Cadmium; D055598:Chemical Phenomena; D002621:Chemistry; D003460:Crystallization; D003545:Cysteine; D008668:Metallothionein; D011487:Protein Conformation; D051381:Rats; D014961:X-Ray Diffraction; D015032:Zinc
chemical_list: D002104:Cadmium; D008668:Metallothionein; D015032:Zinc; D003545:Cysteine