The redox-regulated chaperone Hsp33 is specifically activated upon exposure of cells to peroxide stress at elevated temperatures. Here we show that Hsp33 harbors two interdependent stress-sensing regions located in the C-terminal redox-switch domain of Hsp33: a zinc center sensing peroxide stress conditions and an adjacent linker region responding to unfolding conditions. Neither of these sensors works sufficiently in the absence of the other, making the simultaneous presence of both stress conditions a necessary requirement for Hsp33's full activation. Upon activation, Hsp33's redox-switch domain adopts a natively unfolded conformation, thereby exposing hydrophobic surfaces in its N-terminal substrate-binding domain. The specific activation of Hsp33 by the oxidative unfolding of its redox-switch domain makes this chaperone optimally suited to quickly respond to oxidative stress conditions that lead to protein unfolding.
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We thank S. VanHaerents for excellent technical assistance, J. Bardwell, L. Leichert and T. Tapley for critically reading the manuscript, and Leopoldina Gesellschaft Deutscher Naturforscher for a postdoctoral fellowship to J.W. P.C.F.G. was supported by a Rackham Predoctoral Fellowship. US National Institutes of Health grant GM065318 supported this work.
The authors declare no competing financial interests.
AMS trapping reveals difference in thiol modification patterns of Hsp33 incubated in H2O2 at 30 °C or 43 °C. (PDF 59 kb)
Hsp33's C terminus is predicted to be natively unfolded in the absence of cofactors. (PDF 35 kb)
Peroxide stress does not induce protein aggregation in vivo. (PDF 323 kb)
α-helix content in reduced and oxidized Hsp33. (PDF 115 kb)
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Ilbert, M., Horst, J., Ahrens, S. et al. The redox-switch domain of Hsp33 functions as dual stress sensor. Nat Struct Mol Biol 14, 556–563 (2007) doi:10.1038/nsmb1244
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