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Updated: Jul 3, 2026

In Situ Monitoring of Transiently Formed Molecular Chaperone Assemblies in Bacteria, Yeast, and Human Cells
Published on: September 2, 2019
Functional divergence between co-chaperones of Hsc70
Stefan Tzankov1, Michael J H Wong, Kun Shi
1Department of Biochemistry, McGill University, Montreal, Quebec H3G 1Y6, Canada.
Heat shock cognate 70 kDa protein (Hsc70) chaperone activity is modulated by co-chaperones. Functional divergence exists between Hsc70 co-chaperones, impacting protein refolding and ATPase rates.
Area of Science:
- Molecular Biology
- Protein Folding
- Biochemistry
Background:
- The chaperone Hsc70 (Heat shock cognate 70 kDa protein) functions via an ATPase cycle regulated by co-chaperones.
- Hsp40/DnaJ proteins stimulate Hsc70's ATP hydrolysis and bind unfolded polypeptides.
- Nucleotide exchange factors (NEFs) facilitate ADP-ATP exchange on Hsc70.
Purpose of the Study:
- To analyze the distinct polypeptide binding patterns of Hsp40 co-chaperones DJA1 and DJA2.
- To investigate the influence of DJA1 and DJA2, individually and in combination with NEFs, on Hsc70-mediated protein refolding.
- To explore the functional divergence between Hsc70 co-chaperones.
Main Methods:
- Purification and analysis of Hsp40 co-chaperones DJA1 and DJA2.
- Assessment of polypeptide binding specificities.
- In vitro refolding assays using luciferase as a substrate.
- Measurement of Hsc70 ATPase activity.
- Construction and analysis of a chimeric DJA2 protein.
Main Results:
- DJA2, but not DJA1, stimulated Hsc70-mediated luciferase refolding independently of NEFs.
- NEFs (Bag1, Hsp110) differentially modulated refolding activity with Hsc70 and DJA2, while HspBP1 had no effect.
- DJA1 inhibited refolding mediated by Hsc70 and DJA2.
- All co-chaperone and NEF combinations stimulated Hsc70 ATPase rates, with varying efficiencies.
- A chimeric DJA2 with DJA1's J domain supported polypeptide binding and ATPase stimulation but not efficient refolding.
Conclusions:
- Hsc70 co-chaperones DJA1 and DJA2 exhibit distinct functional properties.
- The J domain of Hsp40 co-chaperones plays a critical role in Hsc70-mediated protein refolding.
- A complex model is proposed for Hsc70 mechanism, highlighting functional divergence among co-chaperones.
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