A biosensor-based framework to measure latent proteostasis capacity.

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Biology

Background:

• Protein quality control (QC) maintains proteostasis but can be depleted in disease.
• Quantitatively defining the capacity of the QC pool has been challenging.
• HSP70 and HSP90 family proteins are key players in protein folding homeostasis.

Purpose of the Study:

• To develop a novel biosensor for quantitatively measuring QC pool capacity.
• To investigate the role of holdase activity in suppressing protein aggregation.
• To understand how proteostasis stimulation and stress affect QC function.

Main Methods:

• Utilized a biosensor system with barnase kernels of varying folding stability.
• Employed flow cytometry and mathematical modeling to assess QC capacity.
• Measured the ability of QC proteins to act as holdases and suppress aggregation.

Main Results:

• The HSP70 chaperone cycle is rate-limited by HSP70 holdase activity under normal conditions.
• Increased BAG1 levels overcome the rate limitation of the HSP70 cycle.
• HSF1 overexpression activates the heat shock gene cluster, impacting QC activity.

Conclusions:

• The developed biosensor system provides a quantitative measure of QC capacity.
• The findings elucidate mechanisms for overcoming rate limitations in chaperone cycles.
• This work opens new avenues for developing disease biosensors and studying proteostasis systems.