Cytosolic Hsp60 can modulate proteasome activity in yeast

Area of Science:

• Cellular Biology
• Molecular Biology
• Protein Degradation

Background:

• Heat shock protein 60 (Hsp60) is a crucial mitochondrial chaperone.
• The role of cytosolic Hsp60 in regulating cellular processes is less understood.
• The proteasome is a key cellular machine for protein degradation.

Purpose of the Study:

• To investigate the interaction between cytosolic Hsp60 and the yeast proteasome.
• To determine if cytosolic Hsp60 can modulate proteasome activity.
• To explore the functional consequences of this interaction on protein turnover.

Main Methods:

• Yeast (Saccharomyces cerevisiae) as a model system.
• Co-expression of cytosolic Hsp60 with proteasome substrates (murine Bax, ΔMTS-Aco1).
• Measurement of protein degradation rates, protein-chaperone association, and proteasome peptidase activity.
• Proteasome pulldown assays and analysis of polyubiquitinated proteins.

Main Results:

• Cytosolic Hsp60 stabilizes Bax and enhances its mitochondrial association and killing capacity.
• Hsp60 inhibits the degradation of cytosolic proteins, including ubiquitin-proteasome substrates.
• Elevated cytosolic Hsp60 correlates with reduced proteasome activity and increased polyubiquitinated proteins.
• Hsp60 physically associates with proteasomes, even in a chaperone-inactive mutant form.

Conclusions:

• Cytosolic Hsp60 directly inhibits yeast proteasome activity.
• Hsp60 localization to the cytosol can modulate proteasome function based on cellular requirements.
• This interaction provides a novel mechanism for regulating protein homeostasis.