Hsp90 provides a platform for kinase dephosphorylation by PP5

Area of Science:

• Molecular Chaperones
• Protein Homeostasis
• Signal Transduction

Background:

• Heat shock protein 90 (Hsp90) is a molecular chaperone essential for the folding and activation of client kinases.
• Cdc37 acts as a cochaperone, and its phosphorylation status influences Hsp90 client kinase activity.
• Phosphatase PP5 dephosphorylates both CRaf and Cdc37 in an Hsp90-dependent manner.

Purpose of the Study:

• To investigate the role of PP5 in dephosphorylating Hsp90-bound kinases and Cdc37.
• To elucidate the structural mechanism by which Hsp90 regulates PP5 activity.
• To clarify the sequence of events involving kinase release and Cdc37 dephosphorylation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of the PP5:Hsp90:Cdc37:CRaf complex.
• Biochemical assays to assess dephosphorylation activity.

Main Results:

• Hsp90-bound kinases sterically hinder Cdc37 dephosphorylation, indicating kinase release is a prerequisite for Cdc37 dephosphorylation.
• The cryo-EM structure reveals Hsp90 activates PP5 and scaffolds it to dephosphorylate CRaf.
• PP5 dephosphorylates CRaf at sites near the kinase domain.

Conclusions:

• Hsp90's function extends beyond folding and activation to include post-translational modification of client kinases.
• Kinase release from Hsp90 must occur before Cdc37 can be dephosphorylated by PP5.
• Hsp90 plays a critical role in regulating kinase activity through dephosphorylation events.