Osmolyte-induced conformational changes in the Hsp90 molecular chaperone

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Osmolytes are vital for cellular homeostasis and stress response, maintaining protein thermodynamic stability.
• While osmolyte effects on protein folding stability are understood, their impact on native-state conformational changes is less clear.
• The Hsp90 molecular chaperone exists in a complex native conformational equilibrium.

Purpose of the Study:

• To investigate the influence of osmolytes on the native-state conformational changes of the Hsp90 molecular chaperone.
• To determine if established osmolyte principles governing protein stability also apply to large-scale protein conformational dynamics.

Main Methods:

• Small-angle X-ray scattering (SAXS) was employed to observe structural changes in Hsp90 within its native ensemble.
• Structure-based fitting of SAXS data, surface area comparisons, and m-value analysis were used to interpret osmolyte effects.
• Ligand-specific conformations (ATP-bound) of Hsp90 were also examined.

Main Results:

• Dramatic osmolyte-dependent structural changes were observed in the native Hsp90 ensemble.
• The extent of osmolyte influence on Hsp90 conformation correlated strongly with their effects on protein stability.
• Osmoytes did not significantly alter the ligand-specific conformation of Hsp90 in the presence of ATP.

Conclusions:

• Established osmolyte principles governing protein stability extend to large-scale protein conformational changes, including cooperative domain-domain interactions.
• Osmoytes can maintain protein conformational heterogeneity, similar to how they maintain protein stability.
• The impact of osmolytes on different structural states of a protein can vary significantly.