title: ALS-causing SOD1 mutations promote production of copper-deficient misfolded species.
abstract: Point mutations scattered throughout the sequence of Cu,Zn superoxide dismutase (SOD1) cause a subset of amyotrophic lateral sclerosis (ALS) cases. SOD1 is a homodimer in which each subunit binds one copper atom and one zinc atom. Inclusions containing misfolded SOD1 are seen in motor neurons of SOD1-associated ALS cases. The mechanism by which these diverse mutations cause misfolding and converge on the same disease is still not well understood. Previously, we developed several time-resolved techniques to monitor structural changes in SOD1 as it unfolds in guanidine hydrochloride. By measuring the rates of Cu and Zn release using an absorbance-based assay, dimer dissociation through chemical cross-linking, and β-barrel conformation changes by tryptophan fluorescence, we established that wild-type SOD1 unfolds by a branched pathway involving a Zn-deficient monomer as the dominant intermediate of the major pathway, and with various metal-loaded and Cu-deficient dimers populated along the minor pathway. We have now compared the unfolding pathway of wild-type SOD1 with those of A4V, G37R, G85R, G93A, and I113T ALS-associated mutant SOD1. The kinetics of unfolding of the mutants were generally much faster than those of wild type. However, all of the mutants utilize the minority pathway to a greater extent than the wild-type protein, leading to greater populations of Cu-deficient intermediates and decreases in Zn-deficient intermediates relative to the wild-type protein. The greater propensity of the mutants to populate Cu-deficient states potentially implicates these species as a pathogenic form of SOD1 in SOD1-associated ALS and provides a novel target for therapeutic intervention.
authors.affiliation: Campbell Family Institute for Cancer Research, Ontario Cancer Institute/University Health Network, Department of Biochemistry, University of Toronto, TMDT 4-305, 101 College Street, Toronto, Ontario, Canada M5G 1L7.
authors.forename: Philbert
authors.initials: P
authors.lastname: Ip
authors.forename: Vikram Khipple
authors.initials: VK
authors.lastname: Mulligan
authors.forename: Avijit
authors.initials: A
authors.lastname: Chakrabartty
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000201:enzymology* / Q000235:genetics; D003300:Copper / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D009154:Mutation; D017510:Protein Folding; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism; D000072105:Superoxide Dismutase-1
chemical_list: C000606290:SOD1 protein, human; D003300:Copper; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1