Pro-Oxidant Copper-Binding Mode of the Apo Form of ALS-Linked SOD1 Mutant H43R Denatured at Physiological Temperature

The mutation of Cu,Zn-superoxide dismutase (SOD1), a major antioxidant enzyme, is associated with amyotrophic lateral sclerosis (ALS). In a previous study, we showed that the metal-depleted apo form of an ALS-linked mutant, H43R, undergoes denaturation at physiological temperature (37 °C) in 90 min and acquires pro-oxidant activity in the presence of Cu2+ and H2O2. In this study, we have examined the Cu2+-binding mode of denatured apo-H43R by circular dichroism (CD), fluorescent oxidation, UV Raman spectroscopy, and photooxidation. CD spectroscopy indicates that denatured apo-H43R loses native β-barrel structure and the binding of Cu2+ to the denatured apo form induces local refolding. Fluorescent-oxidation assays in the absence and presence of Cu2+ chelators show that denatured apo-H43R contains two Cu2+-binding sites with higher and lower Cu2+ affinities and with pro-oxidant activities in the reverse order. UV Raman spectroscopy gives evidence that His residues are bound to Cu2+ mainly through the imida...