Metal migration and subunit swapping in ALS-linked SOD1: Zn2+ transfer between mutant and wild-type occurs faster than the rate of heterodimerization

Oxidation of Dueling Cysteine Promotes Subunit Exchange in SOD1

“…The principal tool used to measure the rate and Δ G Het of heterodimerization, capillary electrophoresis, separates proteins based upon their net charge and hydrodynamic drag in a bare fused-silica capillary. CE is one of the only tools capable of rapidly and accurately measuring the heterodimerization of these two proteins …”

“…CE is one of the only tools capable of rapidly and accurately measuring the heterodimerization of these two proteins. 24 We focused on the E100K mutation because it can be separated from the WT SOD1 at a higher resolution than other ALS mutants that we have studied with CE (isoelectric variants cannot be separated). 52 While the E100K substitution alters the formal net negative charge of each subunit by two units, prior studies with "protein charge ladders" show that the substitution alters the actual net charge of folded solvated SOD1 by +1.89 ± 0.04 units per subunit at pH 7.4.…”

“…22 The mechanism by which WT SOD1 triggers ALS in the A4V SOD1 transgenic mouse or simply enhances symptoms of ALS in other mutant SOD1 mice is unknown 18,23 with mutant SOD1 and (ii) indirect mechanisms, including competition for protective factors such as chaperones or Cu 1+/2+ and Zn 2+ ions. 23,24 A previous study of five ALS mutant SOD1 proteins� including three "cryptic" mutants whose ΔG folding and thermostability are not significantly different from WT SOD1�found that the measured ΔG Het weakly correlated with patient survival time by ∼ +5 years per kJ. Notably, the clinically severe D101N protein, whose survival is as short as the A4V protein (∼2 years), exhibited the most favorable ΔG Het .…”

“…In vivo , the heterodimerization of mutant/WT SOD1 appears to somehow promote the aggregation and neurotoxicity of mutant SOD1. − In transgenic mice expressing ALS mutant SOD1, the coexpression of the WT SOD1 protein can accelerate disease progression. , In one particular case, the A4V SOD1 mouse, the coexpression of WT SOD1 is required for disease onset . The mechanism by which WT SOD1 triggers ALS in the A4V SOD1 transgenic mouse or simply enhances symptoms of ALS in other mutant SOD1 mice is unknown , but could involve: (i) direct interactions with mutant SOD1 and (ii) indirect mechanisms, including competition for protective factors such as chaperones or Cu 1+/2+ and Zn 2+ ions. , …”