Oxidation of Dueling Cysteine Promotes Subunit Exchange in SOD1

Abstract

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-β-SH to sulfinic and sulfonic acid (by hydrogen peroxide) increased rates of heterodimerization (with unoxidized protein) by ∼3-fold. Cysteine oxidation drove the equilibrium free energy of SOD1 heterodimerization by up to ΔΔG = −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.

Cysteine thiol sulfinic acid in plant stress signaling

“…For instance, peroxiredoxins, such as 2‐CysPrxs from various organisms (Iglesias‐Baena et al, 2010, 2011; Jang et al, 2004; Wang et al, 2012; Yang et al, 2002), PrxIIF from pea (Iglesias‐Baena et al, 2011), and PrxQ from Xanthomonas campestris (Perkins et al, 2016). Additionally, the formation of –SO 2 H on Cys‐111 of human superoxide dismutase 1 (SOD1) not only inhibits its enzymatic activity (Xie et al, 2021), but also facilitates subunit exchange between oxidized and unoxidized homodimers, leading to the formation of heterodimers (Zhang et al, 2023). Another well‐known example of enzymatic inactivation is glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH), a key protein in glycolysis, which is affected by –SO 2 H modification in both animal and plant systems (Barinova et al, 2023; Bedhomme et al, 2012).…”