A switch point in the molecular chaperone Hsp90 responding to client interaction.

Area of Science:

• Molecular biology
• Protein biochemistry
• Cellular signaling

Background:

• Heat shock protein 90 (Hsp90) is a molecular chaperone essential for protein homeostasis.
• Hsp90 functions through large conformational changes, with known switch points in its N-terminal (Hsp90-N) and C-terminal (Hsp90-C) domains.
• Switch points within the Hsp90 middle domain (Hsp90-M) are less understood.

Purpose of the Study:

• To identify and characterize novel conformational switch points in the Hsp90 middle domain.
• To elucidate the mechanism by which Hsp90 senses client protein interactions.
• To investigate the role of the Hsp90 middle domain in inter-domain communication.

Main Methods:

• Site-directed mutagenesis of a conserved tryptophan residue in Hsp90-M.
• Biochemical assays to assess Hsp90-client protein interactions.
• Analysis of inter-domain communication using biophysical techniques.

Main Results:

• A conserved tryptophan residue in Hsp90-M acts as a novel conformational switch point.
• This tryptophan senses stringent client protein binding and transmits information via a cation-π interaction with lysine.
• Mutations at this site disrupt inter-domain communication and client-induced Hsp90 conformational cycling.

Conclusions:

• The identified tryptophan residue in Hsp90-M is critical for transmitting client binding information to Hsp90-N.
• This mechanism facilitates the progression of the Hsp90 conformational cycle and efficient client protein processing.
• The study reveals a new regulatory mechanism for Hsp90 chaperone activity.