title: Structural instability and Cu-dependent pro-oxidant activity acquired by the apo form of mutant SOD1 associated with amyotrophic lateral sclerosis.
abstract: Cu,Zn-superoxide dismutase (SOD1) is a cytosolic antioxidant enzyme, and its mutation has been implicated in amyotrophic lateral sclerosis (ALS), a disease causing a progressive loss of motor neurons. Although the pathogenic mechanism of ALS remains unclear, it is hypothesized that some toxic properties acquired by mutant SOD1 play a role in the development of ALS. We have examined the structural and catalytic properties of an ALS-linked mutant of human SOD1, His43Arg (H43R), which is characterized by rapid disease progression. As revealed by circular dichroism spectroscopy, H43R assumes a stable β-barrel structure in the Cu(2+),Zn(2+)-bound holo form, but its metal-depleted apo form is highly unstable and readily unfolds or misfolds into an irregular structure at physiological temperature. The conformational change occurs as a two-state transition from a nativelike apo form to a denatured apo form with a half-life of ∼0.5 h. At the same time as the denaturation, the apo form of H43R acquires pro-oxidant potential, which is fully expressed in the presence of Cu(2+) and H(2)O(2), as monitored with a fluorogenic probe for detecting pro-oxidant activity. Comparison of d-d absorption bands suggests that the Cu(2+) binding mode of the denatured apo form is different from that of the native holo form. The denatured apo form of H43R is likely to provide non-native Cu(2+) binding sites where the Cu(2+) ion is activated to catalyze harmful oxidation reactions. This study raises the possibility that the structural instability and the resultant Cu-dependent pro-oxidant activity of the apo form of mutant SOD1 may be one of the pathogenic mechanisms of ALS.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai, Japan.
authors.forename: Furi
authors.initials: F
authors.lastname: Kitamura
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Fujimaki
authors.forename: Wakana
authors.initials: W
authors.lastname: Okita
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Hiramatsu
authors.forename: Hideo
authors.initials: H
authors.lastname: Takeuchi
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000201:enzymology* / Q000235:genetics*; D001059:Apoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002942:Circular Dichroism; D003300:Copper / Q000378:metabolism*; D018450:Disease Progression; D004795:Enzyme Stability; D006801:Humans; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017382:Reactive Oxygen Species / Q000737:chemistry* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000072105:Superoxide Dismutase-1
chemical_list: D001059:Apoproteins; D050505:Mutant Proteins; D017382:Reactive Oxygen Species; C000606290:SOD1 protein, human; D003300:Copper; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1