Structural Instability and Cu-Dependent Pro-Oxidant Activity Acquired by the Apo Form of Mutant SOD1 Associated with Amyotrophic Lateral Sclerosis

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• 作者：Furi Kitamura ; Nobuhiro Fujimaki ; Wakana Okita ; Hirotsugu Hiramatsu ; Hideo Takeuchi
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：May 24, 2011
• 年：2011
• 卷：50
• 期：20
• 页码：4242-4250
• 全文大小：911K
• 年卷期：v.50,no.20(May 24, 2011)
• ISSN：1520-4995

文摘

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 尾-barrel structure in the Cu²⁺,Zn²⁺-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 Cu²⁺ and H₂O₂, as monitored with a fluorogenic probe for detecting pro-oxidant activity. Comparison of d鈥揹 absorption bands suggests that the Cu²⁺ 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 Cu²⁺ binding sites where the Cu²⁺ 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.