title: Sulfide ions as modulators of metal-thiolate cluster size in a plant metallothionein.
abstract: Metallothioneins are small cysteine-rich proteins coordinating various transition metal ions preferably with the electron configuration d(10). They are ubiquitously present in all phyla, and next to phytochelatins they represent a successful molecular concept for high-capacity metal ion binding. Recent studies showed the incorporation of sulfide ions into the metal-thiolate cluster of metallothionein 2 from the plant Cicer arietinum (cicMT2) increasing the cadmium binding capacity and stability of the cluster. In the present work, the sulfide-induced structural changes accompanying the cluster formation and the sulfide-modulated increase in cluster size are analyzed in detail with a variety of analytical and spectroscopic techniques. Evaluation of the mechanism of sulfide containing Cd(II)-thiolate cluster formation in cicMT2 reveals a strong dependence on the sequence of metal and sulfide additions for successful sulfide incorporation. To probe the general ability of metallothioneins to form sulfide containing larger metal-thiolate clusters, analogous experiments were performed with a mammalian metallothionein. The observation that the cadmium binding ability of rabbit liver MT2A was only slightly increased led to the development of a hypothesis in which the long cysteine-free linker regions present in certain plant metallothioneins may contribute to the accommodation of the respective larger cluster assemblies.
authors: Institute of Inorganic Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
authors: Tamara
authors: T
authors: Huber
authors: Eva
authors: E
authors: Freisinger
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002104:Cadmium / Q000737:chemistry; D029863:Cicer / Q000378:metabolism; D002942:Circular Dichroism / Q000379:methods; D003553:Cystine / Q000737:chemistry; D004583:Electrons; D007477:Ions; D008099:Liver / Q000378:metabolism; D008668:Metallothionein / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D008969:Molecular Sequence Data; D010944:Plants / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D007477:Ions; D008670:Metals; D011994:Recombinant Proteins; D013438:Sulfhydryl Compounds; D013440:Sulfides; D002104:Cadmium; D003553:Cystine; D008668:Metallothionein; D015032:Zinc