Modulation of the Hsp90 chaperone cycle by a stringent client protein

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Heat shock protein 90 (Hsp90) is a crucial molecular chaperone in eukaryotic cells.
• The glucocorticoid receptor (GR) is a stringent client protein whose function relies on Hsp90.
• The precise molecular mechanism of Hsp90-GR interaction remains largely unknown.

Purpose of the Study:

• To elucidate the molecular mechanism of Hsp90-GR interaction.
• To define the binding site of GR on Hsp90.
• To understand how GR binding affects Hsp90's conformational cycle and activity.

Main Methods:

• Reconstitution of Hsp90-GR interaction using purified components.
• Biochemical and structural analyses.
• Förster Resonance Energy Transfer (FRET) experiments to study Hsp90 conformation.
• Measurement of Hsp90 ATPase activity.

Main Results:

• The binding site for GR on Hsp90 was identified.
• GR binding was shown to modulate Hsp90's conformational cycle, favoring a partially closed dimer conformation.
• Hsp90's conformational cycle was decelerated, and its ATPase activity decreased upon GR binding.
• Hsp90 cochaperones were found to differentially regulate Hsp90-GR complex formation.

Conclusions:

• The study defines the Hsp90-GR binding site and reveals that GR binding alters Hsp90 conformation and function.
• Hsp90 cochaperones act as regulatory elements controlling the Hsp90 machinery's progression.
• This work uncovers a complex interplay between client proteins and cochaperones in modulating Hsp90 activity.