A scaffold protein that chaperones a cysteine-sulfenic acid in H2O2 signaling

Abstract

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.

We gratefully acknowledge G. Branlant for his essential input to initiate the project. We also thank A. Gruez for assistance with protein stability optimization; S. Boschi-Muller and F. Talfournier for fruitful discussions and help with quench flow experiments; J.M. Alberto for support with the use of the NGERE U954-INSERM chromatographic facility; and J. Charbonnel and G. Palais for excellent technical support. Microcalorimetry and mass spectrometry were performed respectively at the SCBIM (Federation de Recherche 3209 BMCT) and SCMS platforms of Universite de Lorraine. This work was supported by grants from the Ligue contre le Cancer to S.R.-C., and from ANR ERRed, InCA PLBIO INCA_5869 to M.B.T. A.B. was supported by a PhD fellowship from the French research minister.