Fig 2: (a) Prx1 catalytic cycle. The Prx1 peroxidase cycle and hyperoxidation mechanism are shown at the level of the Prx1 dimeric unit to highlight the conformational state [fully folded (FF) and locally unfolded (LU)] of the active site identified by the peroxidatic Cys CP and C-terminal tail identified by resolving Cys CR. The rate constants of peroxide reduction kSOH, sulfinylation kSO2, resolution kSS, and FF–LU transition kFF and kLU are indicated. (b) Zoom into the catalytic site of Tsa1. The subunit containing the CP is shown in blue, and the subunit containing the CR is shown in yellow (PDB code 3SBC). Residues CP and CR are shown in yellow, W83 and W173 in orange, and W161 in red. Within the C-terminal tail, residues A177 and A178 are highlighted in green and the Y190-F191 motif in purple.

Fig 3: Attribution of phase 2 to a conformational transition. (a) Effect of saccharose (0% black, 10% red, 20% green, and 30% blue) on the reaction of Tsa1 (5 µM) with H2O2 (10 µM) monitored as in Figure 2, fitted against a three-exponential equation (red lines). Inset: effect of saccharose concentration on rate constants k1obs, k2, and k3 normalized to 0% saccharose. The stopped-flow mixer efficiency in viscous solutions was established by mixing Trp and up to 30% saccharose, which showed no artifactual effects on the dilution kinetics (Figure S2). (b) Near-UV circular dichroism spectra of 50 µM wild-type Tsa1 (plain) and Tsa1Y190G F191G (dashed line) under the reduced (black) and disulfide (red) forms. Measurements were performed in a 1 cm cuvette in a phosphate 10 mM and NaF 100 mM buffer (pH 7) and are the average of three records. (c) Pre-steady-state kinetics for the reaction of Tsa1 (5 µM) with H2O2 (5, 10, 25, 50, 100, 200, 400, and 800 µM, light gray to black) monitored as in Figure 2, fitted against a biexponential equation (red lines). Inset: second-order plots and linear fits of the observed rate constants for the fast phase k1obs (circles, black line) and slow phase k3 (diamond, green line). (d) Pre-steady-state kinetics for the reaction of Tsa1 (50 µM) with H2O2 (100 µM) monitored by a near-UV CD signal at 270 nm. The trace is the average of 50 runs, and the first-order fit is shown in red. (e) Effect of saccharose (0% black, 15% red, and 30% blue) on the reaction of human Prx1 (5 µM) with H2O2 (10 µM) monitored as in Figure 2 and fitted against a biexponential equation (red or black lines). Inset: effect of saccharose concentration on the rate constant of the increasing phase normalized to 0% saccharose.

Fig 4: SUCLA2-stress granule signaling controls redox in part by mediating catalase expression. (A) Effect of SUCLA2 loss on global protein biosynthesis. Cells with or without SUCLA2 cultured under detachment conditions were applied to fluorescent-based protein synthesis assay. (B) Levels of metabolic enzymes catalase, PRX1/2/4, SOD2, and FASN in detached SUCLA2 knockdown cells. (C and D) Effect of SUCLA2 knockdown on the enzyme activity of catalase (C) and intracellular hydrogen peroxide levels (D) in A549, H460, and MDA-MB231 cells. (E and F) Effect of stress granule rescue on catalase expression (E) and effect of catalase overexpression on stress granule formation (F) in SUCLA2 knockdown cells. Scale bars represent 5 µm for (E) and (F). Error bars represent ± SD from three replicates for (A, and C–F). P values were obtained by two-tailed Student’s t test for (A, C, and D), and one-way ANOVA for (E and F) (ns: not significant; **P < 0.01).