A scaffold protein that chaperones a cysteine-sulfenic acid in H2O2 signaling
Toledano, Michel B.
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In Saccharomyces cerevisiae, Yap1 regulates an H2O2-inducible transcriptional response that controls cellular H2O2 homeostasis. H2O2 activates Yap1 by oxidation through the intermediacy of the thiol-peroxidase Orp1. Upon reacting with H2O2, Orp1 catalytic cysteine oxidizes to a sulfenic acid, which then engages either into an intermolecular disulfide with Yap1 that leads to Yap1 activation, or an intramolecular disulfide that commits the enzyme into its peroxidatic cycle. Of these two competing reactions, how the former one, which is kinetically unfavorable, occurs? We show that the Yap1-binding-protein Ybp1 brings together Orp1 and Yap1 into a ternary complex that selectively activates condensation of the Orp1 sulfenylated cysteine with one of the six Yap1 cysteines, while inhibiting Orp1 intramolecular disulfide formation. We propose that Ybp1 operates as a scaffold protein and as a sulfenic acid chaperone to provide specificity into the transfer of oxidizing equivalents by a reactive sulfenic acid species.