Voltage-Induced Misfolding of Zinc-Replete ALS Mutant Superoxide Dismutase‑1

The monomerization of Cu, Zn superoxide dismutase (SOD1) is an early step along pathways of misfolding linked to amyotrophic lateral sclerosis (ALS). Monomerization requires the reversal of two post-translational modifications that are thermodynamically favorable: (i) dissociation of active-site metal ions and (ii) reduction of intramolecular disulfide bonds. This study found, using amide hydrogen/deuterium (H/D) exchange, capillary electrophoresis, and lysine-acetyl protein charge ladders, that ALS-linked A4V SOD1 rapidly monomerizes and partially unfolds in an external electric field (of physiological strength), without loss of metal ions, exposure to disulfide-reducing agents, or Joule heating. Voltage-induced monomerization was not observed for metal-free A4V SOD1, metal-free WT SOD1, or metal-loaded WT SOD1. Computational modeling suggested a mechanism for this counterintuitive effect: subunit macrodipoles of dimeric SOD1 are antiparallel and amplified 2-fold by metal coordination, which increases torque at the dimer interface as subunits rotate to align with the electric field

Gibbs Energy of Superoxide Dismutase Heterodimerization Accounts for Variable Survival in Amyotrophic Lateral Sclerosis

The exchange of subunits between homodimeric mutant Cu, Zn superoxide dismutase (SOD1) and wild-type (WT) SOD1 is suspected to be a crucial step in the onset and progression of amyotrophic lateral sclerosis (ALS). The rate, mechanism, and Δ<i>G</i> of heterodimerization (Δ<i>G</i>_Het) all remain undetermined, due to analytical challenges in measuring heterodimerization. This study used capillary zone electrophoresis to measure rates of heterodimerization and Δ<i>G</i>_Het for seven ALS-variant apo-SOD1 proteins that are clinically diverse, producing mean survival times between 2 and 12 years (postdiagnosis). The Δ<i>G</i>_Het of each ALS variant SOD1 correlated with patient survival time after diagnosis (<i>R</i>² = 0.98), with more favorable Δ<i>G</i>_Het correlating with shorter survival by 4.8 years per kJ. Rates of heterodimerization did not correlate with survival time or age of disease onset. Metalation diminished the rate of subunit exchange by up to ∼38-fold but only altered Δ<i>G</i>_Het by <1 kJ mol^–1. Medicinal targeting of heterodimer thermodynamics represents a plausible strategy for prolonging life in SOD1-linked ALS