A Bacteriophage-Encoded J-Domain Protein Interacts with the DnaK/Hsp70 Chaperone and Stabilizes the Heat-Shock Factor σ32 of Escherichia coli

Mitochondria play a central role in the biogenesis of iron–sulfur cluster(s) (FeS), protein cofactors needed for many cellular activities. After assembly on scaffold protein Isu, the cluster is transferred onto a recipient apo-protein. Transfer requires Isu interaction with an Hsp70 chaperone system that includes a dedicated J-domain protein co-chaperone (Hsc20). Hsc20 stimulates Hsp70′s ATPase activity, thus stabilizing the critical Isu–Hsp70 interaction. While most eukaryotes utilize a multifunctional mitochondrial (mt)Hsp70, yeast employ another Hsp70 (Ssq1), a product of mtHsp70 gene duplication. Ssq1 became specialized in FeS biogenesis, recapitulating the process in bacteria, where specialized Hsp70 HscA cooperates exclusively with an ortholog of Hsc20. While it is well established that Ssq1 and HscA converged functionally for FeS transfer, whether these two Hsp70s possess similar biochemical properties was not known. Here, we show that overall HscA and Ssq1 biochemical properties are very similar, despite subtle differences being apparent - the ATPase activity of HscA is stimulated to a somewhat higher levels by Isu and Hsc20, while Ssq1 has a higher affinity for Isu and for Hsc20. HscA/Ssq1 are a unique example of biochemical convergence of distantly related Hsp70s, with practical implications, crossover experimental results can be combined, facilitating understanding of the FeS transfer process.

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Roles and regulation of the heat shock ? factor ?32 in Escherichia coli

Antonie van Leeuwenhoek ◽

10.1007/bf00548931 ◽

1990 ◽

Vol 58 (3) ◽

pp. 187-190 ◽

Cited By ~ 10

Author(s):

Takashi Yura ◽

Yasuo Kawasaki ◽

Noriko Kusukawa ◽

Hiroki Nagai ◽

Chieko Wada ◽

...

Keyword(s):

Escherichia Coli ◽

Heat Shock ◽

Heat Shock Factor

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Essentiality of Sis1, a J-domain protein Hsp70 cochaperone, can be overcome by Tti1, a specialized PIKK chaperone

Molecular Biology of the Cell ◽

10.1091/mbc.e21-10-0493 ◽

2021 ◽

Author(s):

Brenda A. Schilke ◽

Elizabeth A. Craig

Keyword(s):

Saccharomyces Cerevisiae ◽

Heat Shock ◽

Essential Gene ◽

Specific Inhibitor ◽

The Other ◽

Phosphatidylinositol 3 Kinase ◽

Complex Cells ◽

J Domain ◽

Domain Protein ◽

Transcription Factor 1

J-domain protein cochaperones drive much of the functional diversity of Hsp70-based chaperone systems. Sis1 is the only essential J-domain protein of the cytosol/nucleus of Saccharomyces cerevisiae. Why it is required for cell growth is not understood, nor is how critical its role in regulation of heat shock transcription factor 1 (Hsf1). We report that single residue substitutions in Tti1, a component of the heterotrimeric TTT complex, a specialized chaperone system for phosphatidylinositol 3-kinase-related kinase (PIKK) proteins, allow growth of cells lacking Sis1. Upon depletion of Sis1, cells become hypersensitive to rapamycin, a specific inhibitor of TORC1 kinase. In addition, levels of the three essential PIKKs (Mec1, Tra1, and Tor2), as well as Tor1, decrease upon Sis1depletion. Overexpression of Tti1 allows growth, without an increase in the other subunits of the TTT complex, Tel2 and Tti2, suggesting that it can function independent of the complex. Cells lacking Sis1, with viability supported by Tti1 suppressor, substantially upregulate some, but not all, heat shock elements activated by Hsf1. Together, our results suggest that Sis1 is required as a cochaperone of Hsp70 for the folding/maintenance of PIKKs making Sis1 an essential gene, and its requirement for Hsf1 regulation is more nuanced than generally appreciated.

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