Aha1 regulates Hsp90's conformation and function in a stoichiometry-dependent way

Area of Science:

• Molecular Biology
• Biochemistry
• Cellular Biology

Background:

• Heat shock protein 90 (Hsp90) is a crucial molecular chaperone for protein homeostasis in eukaryotes.
• Co-chaperones, like Aha1 (activator of Hsp90 ATPase), modulate Hsp90 activity in vital cellular processes.
• The precise mechanism of Hsp90 and Aha1 interaction remains incompletely understood.

Purpose of the Study:

• To elucidate the binding stoichiometry between Hsp90 and Aha1.
• To investigate how Aha1 binding affects Hsp90's conformation, kinetics, ATPase activity, and stability.
• To explore the regulatory role of Aha1 stoichiometry in Hsp90 function.

Main Methods:

• Biochemical assays to determine Hsp90-Aha1 binding stoichiometry.
• Analysis of Hsp90 conformation, kinetics, and ATPase activity under varying Aha1 concentrations.
• Assessment of Hsp90 stability in the presence of different Aha1 binding levels.

Main Results:

• One to two Aha1 molecules bind to a single Hsp90 dimer.
• Binding stoichiometry significantly impacts Hsp90's ATPase activity and middle domain unfolding.
• Conformational equilibrium and kinetics of Hsp90 are minimally affected by Aha1 binding stoichiometry.

Conclusions:

• Aha1 stoichiometry is a key regulatory mechanism for Hsp90 function, extending beyond conformational changes.
• Dual Aha1 binding enhances Hsp90's ATPase activity and promotes middle domain unfolding.
• This study reveals a nuanced regulatory interplay between Hsp90 and its co-chaperone Aha1.