Visualizing the transiently populated closed-state of human HSP90 ATP binding domain

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Medicine

Background:

• Heat shock protein 90 (HSP90) are crucial molecular chaperones.
• HSP90 facilitates the folding of numerous client proteins, including those implicated in cancer and neurodegenerative diseases.
• The functional cycle of HSP90 involves large, ATP-dependent structural rearrangements, but these dynamics in the absence of ATP (apo state) remain poorly understood.

Purpose of the Study:

• To investigate the structural dynamics of the isolated human HSP90α ATP binding domain.
• To determine if apo HSP90 samples distinct structural states relevant to its function.
• To characterize the nature and implications of any identified structural rearrangements.

Main Methods:

• Solution Nuclear Magnetic Resonance (NMR) spectroscopy to characterize ground and excited states.
• Site-directed mutagenesis to probe protein structure and dynamics.
• NMR relaxation measurements to derive kinetic and thermodynamic parameters.
• Molecular dynamics simulations to analyze conformational states and interconversions.

Main Results:

• Identification of a metastable excited state in the human HSP90α ATP binding domain.
• Demonstration that the isolated domain transiently samples a functionally relevant ATP-lid closed state.
• The excited closed state is conformationally distinct (over 30 Å) from the ground state.
• NMR relaxation and simulations confirmed the excited state as metastable and characterized the interconversion dynamics.

Conclusions:

• The human HSP90α ATP binding domain exists in dynamic equilibrium, sampling both ground and metastable excited states.
• The transiently accessed closed conformation provides insights into HSP90’s functional mechanism in its apo state.
• Detailed structural and dynamic information on HSP90α can inform the development of novel therapeutic strategies targeting HSP90-dependent diseases.