Redox silencing of copper in metal-linked neurodegenerative disorders: reaction of Zn7metallothionein-3 with Cu2+ ions.
Dysregulation of copper and zinc homeostasis in the brain plays a critical role in Alzheimer disease (AD). Copper binding to amyloid-beta peptide (Abeta) is linked with the neurotoxicity of Abeta and free radical damage. Metallothionein-3 (MT-3) is a small cysteine- and metal-rich protein expressed in the brain and found down-regulated in AD. This protein occurs intra- and extracellularly, and it plays an important role in the metabolism of zinc and copper. In cell cultures Zn7MT-3, by an unknown mechanism, protects neurons from the toxicity of Abeta. We have, therefore, used a range of complementary spectroscopic and biochemical methods to characterize the interaction of Zn7MT-3 with free Cu2+ ions. We show that Zn7MT-3 scavenges free Cu2+ ions through their reduction to Cu+ and binding to the protein. In this reaction thiolate ligands are oxidized to disulfides concomitant with Zn2+ release. The binding of the first four Cu2+ is cooperative forming a Cu(I)4-thiolate cluster in the N-terminal domain of Cu4,Zn4MT-3 together with two disulfides bonds. The Cu4-thiolate cluster exhibits an unusual stability toward air oxygen. The results of UV-visible, CD, and Cu(I) phosphorescence at 77 K suggest the existence of metal-metal interactions in this cluster. We have demonstrated that Zn7MT-3 in the presence of ascorbate completely quenches the copper-catalyzed hydroxyl radical (OH.) production. Thus, zinc-thiolate clusters in Zn7MT-3 can efficiently silence the redox-active free Cu2+ ions. The biological implication of our studies as to the protective role of Zn7MT-3 from the Cu2+ toxicity in AD and other neurodegenerative disorders is discussed.
Meloni
Gabriele
G
Department of Biochemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
Faller
Peter
P
Vasák
Milan
M
D000544:Alzheimer Disease / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D002413:Cations, Divalent; D002942:Circular Dichroism; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D019610:Cytoprotection; D015536:Down-Regulation; D006801:Humans; D017665:Hydroxyl Radical / Q000737:chemistry* / Q000378:metabolism; D008668:Metallothionein / Q000737:chemistry* / Q000378:metabolism; D009474:Neurons / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding; D011994:Recombinant Proteins; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry* / Q000378:metabolism
D016229:Amyloid beta-Peptides; D002413:Cations, Divalent; D011994:Recombinant Proteins; D017665:Hydroxyl Radical; D003300:Copper; D008668:Metallothionein; D015032:Zinc