Cadmium in metallothioneins

Metallothioneins (MTs) are low-molecular-mass cysteine-rich proteins with the ability to bind mono- and divalent metal ions with the electron configuration d10 in form of metal-thiolate clusters. MTs are thought, among others, to play a role in the homeostasis of essential Zn(II) and Cu(I) ions. Besides these metal ions also Cd(II) can be bound to certain MTs in vivo, giving rise to the perception that another physiological role of MTs is in the detoxification of heavy metal ions. Substitution of the spectroscopically silent Zn(II) ions in metalloproteins by Cd(II) proved to be an indispensable tool to probe the Zn(II) sites in vitro. In this review, methods applied in the studies of structural and chemical properties of Cd-MTs are presented. The first section focuses on the physical basis of spectroscopic techniques such as electronic absorption, circular dichroism (CD), magnetic CD, X-ray absorption, and perturbed angular correlation of gamma-rays spectroscopy, as well as mass spectrometry, and their applications to Cd-MTs from different organisms. The following is devoted to the discussion of metal binding affinities of Cd-MTs, cluster dynamics, the reactivity of bound Cd(II) ions with metal ion chelators and of thiolate ligands with alkylating and oxidizing agents. Finally, a brief summary of the known three-dimensional structures of Cd-MTs, determined almost exclusively by multinuclear NMR techniques, is presented. Besides Cd-MTs, the described methods can also be applied to the study of metal binding sites in other metalloproteins

Metallothionein-3, Zinc, and Copper in the Central Nervous System

Metallothionein-3 (MT-3), also known as the neuronal growth inhibitory factor, has been discovered by Uchida and coworkers in 1991 in their search for a cellular component responsible for antagonizing aberrant neuritic sprouting and increased survival of cultured neurons stimulated by Alzheimer’s disease (AD) brain extract. Since this initial discovery further studies showed that MT-3 possesses peculiar structural and functional properties not shared by other members of the mammalian MT family. Several lines of evidence suggest that the metal-binding protein MT-3 plays a vital role in zinc and copper homeostasis in the brain. Although far from being understood, the unusual structural properties of MT-3 are responsible for its neuronal growth inhibitory activity, involvement in trafficking of zinc vesicles in the CNS, protection against copper-mediated toxicity in AD and in controlling abnormal metal-protein interactions in other neurodegenerative disorders

Structure and Function of Vertebrate Metallothioneins

In 1957, Margoshes and Vallee reported on the isolation of a protein from horse kidney, which showed a high affinity for cadmium, and soon thereafter the protein was named metallothionein (MT) by the leading scientists Kägi and Vallee. Fifty years of intense research has dissected out many of the biochemical, molecular, and genetic aspects of these proteins, yet not that much is understood on its physiological putative functions. Being a highly conserved family of proteins would suggest essential biological functions, but these may be dispensable and/or assumed by other proteins as demonstrated by the phenotype of knock-out mice in normal conditions. Nevertheless, under challenging conditions (such as tissue injury) a strong phenotype appears that is suggestive of important physiological functions. This has been particularly well shown in the brain, where antiinflammatory, antioxidant and antiapoptotic effects of MT have been demonstrated. To date, the results gathered strongly support a therapeutic value of these proteins that deserve attention in clinical studies

Metal-Thiolate Clusters in the C-Terminal Domain of Human Neuronal Growth Inhibitory Factor (GIF)

: Neuronal growth inhibitory factor (GIF), a metallothionein-like protein (metallothionein-3), impairs the survival and neurite formation of cultured neurons. Native GIF contains 4 Cu(I) and three Zn(II) ions organized in homometallic metal-thiolate clusters. However, the cluster localization is not known. In this study, the metal-thiolate clusters formed with monovalent and divalent metal ions in the C-terminal domain of human GIF [GIF(32-68)] containing 11 cysteines were investigated. The cluster formation was followed by using electronic absorption, circular dichroism (CD), and magnetic circular dichroism (MCD) spectroscopy, and in the case of Cu(I) complexes also by luminescence spectroscopy at 77 K. Spectroscopic studies on the Cu(I)-GIF(32-68) complexes showed the successive formation of two air-sensitive Cu 4 S 8-9 - and Cu 6 S 11 -clusters. With Zn(II) and Cd(II) ions, a well-defined M 4 S 11 -cluster is formed in which each metal ion is tetrahedrally coordinated by cy..

Evidence for Cu(I) clusters and Zn(II) clusters in neuronal growth-inhibitory factor isolated from bovine brain

etallothionein. By analogy with Cu 8 -metallothionein, we propose the presence of a Cu 4 cluster with similar electronic structure in native GIF. However, the determined Cys/Cu 1 ratio of approximately 2 : 1 in Cu, Zn-GIF is higher than the ratio found in mammalian Cu(I)-metallothionein forms (approximately 1.6 : 1), which implies that the coordination geometry of Cu 1 -binding sites is different in the Cu 4 cluster. The spectroscopic characterization of Zn 21 -substituted and Cd 21 -substituted GIF (627 metal ions/protein) showed CD and MCD features at positions identical to those reported for the well-characterized mammalian Zn 7 -metallothionein and Cd 7 -metallothionein. Therefore, it is inferred that the cluster organization in GIF with divalen

Modulation of DNA Binding of a Tramtrack Zinc Finger Peptide by the Metallothionein-Thionein Conjugate Pair

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Reactivity of an antimetastatic organometallic ruthenium compound with metallothionein-2: relevance to the mechanism of action

The reaction of metallothionein-2 (MT-2) with the organometallic antitumour compound [Ru(eta(6)-p-cymene)Cl-2(pta)], RAPTA-C, was investigated using ESI MS and ICP AES. The studies were performed in comparison to cisplatin and significant differences in the binding of the two complexes were observed. RAPTA-C forms monoadducts with MT-2, at variance with cisplatin, that has been observed to form up to four adducts. These data, combined with ICP AES analysis, show that binding of both RAPTA-C and cisplatin to MT-2 requires the displacement of an equivalent amount of zinc, suggesting that Cys residues are the target binding sites for the two metallodrugs. The competitive binding of RAPTA-C and cisplatin towards a mixture of ubiquitin (Ub) and MT-2 was also studied, showing that MT-2 can abstract RAPTA-C from Ub more efficiently than it can abstract cisplatin. The mechanistic implications of these results are discussed