Roles of Hydration in Protein-Ligand Binding: Passive or Active Participant?

Area of Science:

• Molecular Biophysics
• Biochemistry

Background:

• Hydration significantly impacts protein dynamics, structure, stability, and interactions in solution.
• Native mass spectrometry (nMS) allows analysis of biomolecules in their native solution states, including hydration effects.
• Understanding hydration's role is crucial for deciphering protein function and interactions.

Purpose of the Study:

• To investigate whether hydration acts as a passive solvent or an active modulator of ligand binding.
• To explore the influence of hydration on protein conformation, stability, and binding thermodynamics.
• To determine the thermodynamic basis of hydration's effect on protein-ligand interactions.

Main Methods:

• Variable-temperature electrospray ionization native mass spectrometry (nMS).
• Analysis of temperature-dependent average charge state (Zavg) and ADP equilibrium binding affinities (Ka) for GroEL single ring mutant (SR1).
• Comparison of thermodynamic parameters, including enthalpy-entropy compensation (EEC), in H2O and D2O.

Main Results:

• Protein conformational changes were indicated by temperature-dependent shifts in Zavg for SR1-ADP complexes in both H2O and D2O.
• Differences in nucleotide binding affinities between H2O and D2O suggest hydration modulates ligand binding.
• Distinct patterns of enthalpy-entropy compensation (EEC) were observed in D2O compared to H2O, revealing hydration's thermodynamic influence.

Conclusions:

• Hydration actively participates in modulating ligand binding, rather than acting as a passive solvent.
• Changes in hydration significantly affect protein conformation, stability, and binding thermodynamics.
• The findings provide critical insights into the molecular mechanisms by which hydration influences protein-ligand interactions.