title: Cupric ions induce the oxidation and trigger the aggregation of human superoxide dismutase 1.
abstract: BACKGROUND
  Amyotrophic lateral sclerosis (ALS), partly caused by the mutations and aggregation of human copper, zinc superoxide dismutase (SOD1), is a fatal degenerative disease of motor neurons. Because SOD1 is a major copper-binding protein present at relatively high concentration in motor neurons and copper can be a harmful pro-oxidant, we want to know whether aberrant copper biochemistry could underlie ALS pathogenesis. In this study, we have investigated and compared the effects of cupric ions on the aggregation of ALS-associated SOD1 mutant A4V and oxidized wild-type SOD1.
  
  
  RESULTS
  As revealed by 90° light scattering, dynamic light scattering, SDS-PAGE, and atomic force microscopy, free cupric ions in solution not only induce the oxidation of either apo A4V or Zn2-A4V and trigger the oligomerization and aggregation of oxidized A4V under copper-mediated oxidative conditions, but also trigger the aggregation of non-oxidized form of such a pathogenic mutant. As evidenced by mass spectrometry and SDS-PAGE, Cys-111 is a primary target for oxidative modification of pathological human SOD1 mutant A4V by either excess Cu(2+) or hydrogen peroxide. The results from isothermal titration calorimetry show that A4V possesses two sets of independent binding sites for Cu(2+): a moderate-affinity site (10(6) M(-1)) and a high-affinity site (10(8) M(-1)). Furthermore, Cu(2+) binds to wild-type SOD1 oxidized by hydrogen peroxide in a way similar to A4V, triggering the aggregation of such an oxidized form.
  
  
  CONCLUSIONS
  We demonstrate that excess cupric ions induce the oxidation and trigger the aggregation of A4V SOD1, and suggest that Cu(2+) plays a key role in the mechanism of aggregation of both A4V and oxidized wild-type SOD1. A plausible model for how pathological SOD1 mutants aggregate in ALS-affected motor neurons with the disruption of copper homeostasis has been provided.
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.forename: Wen-Chang
authors.initials: WC
authors.lastname: Xu
authors.forename: Zhen-Sheng
authors.initials: ZS
authors.lastname: Xie
authors.forename: Kai
authors.initials: K
authors.lastname: Pan
authors.forename: Jiao
authors.initials: J
authors.lastname: Hu
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Dai-Wen
authors.initials: DW
authors.lastname: Pang
authors.forename: Fu-Quan
authors.initials: FQ
authors.lastname: Yang
authors.forename: Yi
authors.initials: Y
authors.lastname: Liang
mesh_terms: D000595:Amino Acid Sequence; D002413:Cations, Divalent; D003300:Copper / Q000737:chemistry*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D010084:Oxidation-Reduction; D066329:Protein Aggregates; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D012996:Solutions; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000235:genetics; D000072105:Superoxide Dismutase-1; D013816:Thermodynamics
chemical_list: D002413:Cations, Divalent; D066329:Protein Aggregates; D011994:Recombinant Proteins; C000606290:SOD1 protein, human; D012996:Solutions; D003300:Copper; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1