Oxidation of Dueling Cysteine Promotes Subunit Exchange in SOD1

The heterodimerization of wild-type (WT) Cu, Zn superoxide dismutase-1 (SOD1) and mutant SOD1 might be a critical step in the pathogenesis of SOD1-linked amyotrophic lateral sclerosis (ALS). Post-translational modifications that accelerate SOD1 heterodimerization remain unidentified. Here, we used capillary electrophoresis to quantify the effect of cysteine-111 oxidation on the rate and free energy of ALS mutant/WT SOD1 heterodimerization. The oxidation of Cys111-beta-SH to sulfinic and sulfonic acid (by hydrogen peroxide) increased rates of heterodimerization (with unoxidized protein) by similar to 3-fold. Cysteine oxidation drove the equilibrium free energy of SOD1 heterodimerization by up to Delta Delta G = -5.11 +/- 0.36 kJ mol-1. Molecular dynamics simulations suggested that this enhanced heterodimerization, between oxidized homodimers and unoxidized homodimers, was promoted by electrostatic repulsion between the two dueling Cys111-SO2-/SO3 -, which point toward one another in the homodimeric state. Together, these results suggest that oxidation of Cys-111 promotes subunit exchange between oxidized homodimers and unoxidized homodimers, regardless of whether they are mutant or WT dimers.

Automated summary

The heterodimerization between wild-type and mutant SOD1 plays a critical role in the development of SOD1-linked ALS. It was found that oxidation of Cys111 can accelerate the rate and increase the free energy of SOD1 heterodimerization. This enhanced heterodimerization is due to electrostatic repulsion between the oxidized and unoxidized forms of SOD1.