The yeast Hsp70 Ssa1 is a sensor for activation of the heat shock response by thiol-reactive compounds

Abstract

Diverse thiol-reactive compounds are found to activate the Hsf1-regulated heat shock response in Saccharomyces cerevisiae. The highly conserved cytosolic Hsp70 protein chaperone is shown to act as a sensor for these molecules through a pair of reactive cysteine residues in the nucleotide-binding domain.

Hierarchical Functional Specificity of Cytosolic Heat Shock Protein 70 (Hsp70) Nucleotide Exchange Factors in Yeast

“…It is thought that Hsp70/Hsp90 associates with DNA-bound yeast Hsf1, maintaining it in a transcriptionally inactive state (59). We and others have previously shown that deletion of either SSE1 or FES1 results in constitutive HSR up-regulation (37,43,63). To comprehensively determine how the loss of the NEFs affects the HSR, we determined Hsf1 activity using a well documented HSE-lacZ reporter system (51).…”

“…Alternatively, general protein folding may not be severely affected, and rather inhibition of Hsf1 transcriptional function by Hsp70, perhaps as part of the Hsp90 supercomplex, could be abrogated leading to HSR derepression. In support of this conjecture, we recently demonstrated that modification of key cysteine residues in Ssa1 is sufficient to induce the HSR (63). At this time it is not possible to mechanistically deconvolute these two models because both ultimately converge on the same fundamental aspect of Hsp70 function.…”

Peroxiredoxin Chaperone Activity Is Critical for Protein Homeostasis in Zinc-deficient Yeast*

“…Preparation of Soluble and Insoluble Proteins from Yeast Cells-Insoluble protein aggregates were separated from soluble proteins using a centrifugation method based on two previously published protocols (36,37). Thirty five-ml cultures were grown to a density of 4 ϫ 10 6 cells/ml (A 600 Ϸ0.4).…”

Sir2 links the unfolded protein response and the heat shock response in a stress response network

“…Hence, although biochemical and genetic evidence suggest that the Hsp90 complex represses Hsf1 activity also in yeast, dissociation of Hsf1 from this chaperone is accompanied neither by translocation to the nucleus nor by homotrimerization. The Hsp70 Ssa1 is another chaperone implicated in Hsf1 regulation; two conserved cysteines in Ssa1, which represses Hsf1 in the absence of stress, are modified by thiol-reactive compounds but not by heat shock, demonstrating that Ssa1 can discriminate between two distinct environmental stresses [10]. In addition, cooperative Hsf1-HSE interactions are strengthened and stabilized by Hsf1 hyperphosphorylation, with distinct patterns and kinetics in response to either heat shock or oxidative stress [11].…”