Two chaperone sites in Hsp90 differing in substrate specificity and ATP dependence

Area of Science:

• Molecular Biology
• Protein Folding
• Cellular Stress Response

Background:

• Heat shock protein 90 (Hsp90) is a crucial molecular chaperone regulating protein structure in eukaryotic cytosol.
• Hsp90 substrates are specific under physiological conditions but become more general under cellular stress.
• The precise mechanism of Hsp90's diverse functions remained largely unknown.

Purpose of the Study:

• To elucidate the functional mechanism of conserved Hsp90 domains.
• To investigate how Hsp90 performs both specific and general chaperone roles.
• To understand the role of ATP binding and cochaperones in Hsp90 activity.

Main Methods:

• Analysis of conserved Hsp90 domains.
• Characterization of N-terminal and C-terminal fragment functions.
• Investigation of ATP-dependent and independent binding mechanisms.
• Assessment of the effect of the antitumor drug geldanamycin.

Main Results:

• Hsp90 possesses two distinct chaperone sites in its N-terminal and C-terminal fragments.
• The C-terminal fragment binds partially folded proteins ATP-independently, potentially regulated by cochaperones.
• The N-terminal domain binds peptides longer than 10 amino acids, with dissociation induced by ATP binding.
• Geldanamycin inhibits Hsp90 ATPase activity and promotes peptide release.

Conclusions:

• The dual chaperone sites of Hsp90, combined with cochaperone specificity, allow for both targeted protein folding and general stress-response functions.
• This mechanism explains Hsp90's ability to manage specific client proteins and adapt to cellular stress.
• The findings provide insight into Hsp90's role in protein homeostasis and disease.