Post­translational Modifications Promote Formation of SOD1 Oligomers With Potential Toxicity in ALS

Abstract

Mutation of the ubiquitous cytosolic enzyme Cu/Zn superoxide dismutase (SOD1) causes a subset of cases of familial amyotrophic lateral sclerosis (FALS) through structural destabilization of SOD1, which leads to misfolding and aggregation. The non‐heritable (sporadic) nature of most cases of ALS and the late onset of symptoms, even for patients expressing disease‐linked mutant proteins throughout life, suggest a significant role of environmental factor(s) in ALS etiology. We have previously found that SOD1 from human tissue is extensively post‐translationally modified, with the most prevalent modifications being glutathionylation at Cys‐111 and phosphorylation at Thr‐2. We further found that glutathionylation significantly destabilizes SOD1WT dimers, increasing the equilibrium dissociation constant approximately 1,000‐fold, such that its stability is comparable to the A4V FALS‐causative mutation. SOD1A4V is further destabilized by glutathionylation. Using computational structural modeling, we show that glutathionylation has distinct effects on different ALS‐linked SOD1 mutants, which correspond to changes in composition of the dimer interface. Glutathionylation also stabilizes an intermediate misfolded species in which the b‐barrel core of each monomer is “loosened”. These findings suggest a mode by which the cellular environment impacts the propensity of SOD1 to adopt toxic misfolded conformations in ALS.