Depletion of the Protein Hydration Shell with Increasing Temperature Observed by Small-Angle X-ray Scattering and...

Area of Science:

• Structural biology
• Biophysics
• Physical chemistry

Background:

• The protein hydration shell is crucial for protein function, influencing conformational changes, molecular recognition, and enzyme activity.
• Understanding hydration shell structure is limited due to a lack of high-resolution, sensitive probes.
• Spectroscopic techniques have elucidated hydration shell dynamics, but structural insights remain scarce.

Purpose of the Study:

• To investigate the temperature sensitivity of protein hydration shells using a novel structural approach.
• To provide high spatial resolution insights into the structural changes of hydration shells with varying temperatures.
• To correlate hydration shell behavior with temperature-dependent biological processes.

Main Methods:

• Combined temperature-ramp small-angle X-ray scattering (T-ramp SAXS) experiments across a temperature range of 255 K to 335 K.
• Utilized explicit-solvent small-angle X-ray scattering (SAXS) molecular simulations for detailed structural predictions.
• Analyzed changes in protein contrast and radii of gyration as indicators of hydration shell structural alterations.

Main Results:

• Demonstrated remarkable temperature sensitivity of hydration shells for the IgG-binding domain of Protein G (GB3) and villin headpiece.
• Observed consistent decays in protein contrasts and radii of gyration with increasing temperature for folded proteins.
• Attributed hydration shell depletion to both increased disorder and partial displacement of surface-coordinated water molecules.

Conclusions:

• T-ramp SAXS and explicit-solvent SAXS calculations offer a novel structural perspective on protein hydration shells.
• The temperature-sensitive nature of hydration shells plays a fundamental role in processes like cold denaturation, thermophoresis, and biomolecular phase separation.
• This research provides a structural basis for understanding how temperature influences protein-solution interactions and functions.