title: A novel variant of human superoxide dismutase 1 harboring amyotrophic lateral sclerosis-associated and experimental mutations in metal-binding residues and free cysteines lacks toxicity in vivo.
abstract: Mutations in superoxide dismutase 1 (SOD1) cause familial amyotrophic lateral sclerosis. The Cu-binding capacity of SOD1 has spawned hypotheses that implicate metal-mediated production of reactive species as a potential mechanism of toxicity. In past experiments, we have tested such hypotheses by mutating residues in SOD1 that normally coordinate the binding of Cu, finding that such mutants retain the capacity to induce motor neuron disease. We now describe the lack of disease in mice that express a variant of human SOD1 in which residues that coordinate the binding of Cu and Zn have been mutated (SODMD). SODMD encodes three disease-causing and four experimental mutations that ultimately eliminate all histidines involved in the binding of metals; and includes one disease-causing and one experimental mutation that eliminate secondary metal binding at C6 and C111. We show that the combined effect of these mutations produces a protein that is unstable but does not aggregate on its own, is not toxic, and does not induce disease when co-expressed with high levels of wild-type SOD1. In cell culture models, we determine that the combined mutation of C6 and C111 to G and S, respectively, dramatically reduces the aggregation propensity of SODMD and may account for the lack of toxicity for this mutant.
authors.affiliation: Department of Neuroscience, Center for Translational Research in Neurodegenerative Disease, McKnight Brain Institute, University of Florida, Gainesville, Florida, USA.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Prudencio
authors.forename: Herman
authors.initials: H
authors.lastname: Lelie
authors.forename: Hilda H
authors.initials: HH
authors.lastname: Brown
authors.forename: Julian P
authors.initials: JP
authors.lastname: Whitelegge
authors.forename: Joan S
authors.initials: JS
authors.lastname: Valentine
authors.forename: David R
authors.initials: DR
authors.lastname: Borchelt
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics*; D000818:Animals; D001665:Binding Sites; D015152:Blotting, Northern; D002478:Cells, Cultured; D003300:Copper / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry*; D057809:HEK293 Cells; D006639:Histidine / Q000737:chemistry; D006801:Humans; D007150:Immunohistochemistry; D008670:Metals / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics* / Q000502:physiology*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D013116:Spinal Cord / Q000166:cytology / Q000378:metabolism; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics* / Q000633:toxicity*; D000072105:Superoxide Dismutase-1; D014162:Transfection; D015032:Zinc / Q000378:metabolism
chemical_list: D008670:Metals; D012333:RNA, Messenger; C000606290:SOD1 protein, human; D006639:Histidine; D003300:Copper; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D015032:Zinc; D003545:Cysteine