The Dual Role of Active Site Hydroxylated Residue in Peroxiredoxin Sulfinylation Catalysis

<b><i>Aims:</i></b> Peroxiredoxins (Prx) are ubiquitous Cys peroxidases regulated by sulfinylation, a modification that occurs when the sulfenic acid generated on the catalytic Cys by peroxide reduction reacts with a second molecule of peroxide. In the Prx1 family, sulfinylation sensitivity is controlled by competition between a structural transition from a fully folded (FF) to locally unfolded (LU) conformation and the chemical step of sulfinylation. The initial peroxide reduction relies on a conserved catalytic hydroxylated residue that allows peroxide optimal activation. This study aimed at investigating the role of this catalytic residue in sulfinylation. <b><i>Results:</i></b> Sulfenate attack on peroxide was favored by one order of magnitude when a catalytic Thr was present, for yeast cytosolic Prx1-type enzymes, human Prx1 and yeast mitochondrial Prx, a Prx6-type enzyme. Furthermore, pKa determination supported the notion of electrostatic interaction between the catalytic hydroxyl and sulfenate intermediate. Finally, FF-LU transition kinetics was faster with a catalytic Thr, supporting that the hydroxyl group proximity to the nascent sulfenate group also promotes the FF-LU transition. <b><i>Innovation:</i></b> We identify a major mechanism that activates sulfinylation in hyperoxidation-sensitive Prxs from the Prx1 and Prx6 families. Furthermore, we show that the catalytic hydroxylated residue holds a dual role in regulating hyperoxidation sensitivity, by activating the sulfinylation reaction, while also promoting the competing FF to LU transition, thus acting as an important regulatory determinant. <b><i>Conclusion:</i></b> The present work sets the basis for investigating other instances of Cys proteins regulated by sulfinylation, a modification increasingly recognized in cell redox regulation and signaling. <i>Antioxid. Redox Signal.</i> 43, 1-13.