Two structural relaxations in protein hydration water and their dynamic crossovers

Area of Science:

• Biophysics
• Physical Chemistry
• Computational Biology

Background:

• Hydration water dynamics near biomolecules are crucial for protein function.
• Understanding these dynamics is complex due to interactions with protein structure.
• Molecular dynamics simulations offer a powerful tool to probe these interactions.

Purpose of the Study:

• To investigate the translational single-particle dynamics of lysozyme hydration water.
• To characterize the relaxation behaviors of hydration water upon cooling.
• To elucidate the coupling between water dynamics and protein structural fluctuations.

Main Methods:

• Utilizing molecular dynamics simulations to model lysozyme and its surrounding water.
• Analyzing translational single-particle dynamics of water molecules.
• Characterizing relaxation times and identifying dynamic crossovers as a function of temperature.

Main Results:

• Two distinct relaxations were identified in hydration water near lysozyme.
• The faster relaxation corresponds to the structural alpha-relaxation, observed in bulk water.
• The slower relaxation is attributed to dynamic coupling with protein structure fluctuations.
• Both relaxation times exhibit temperature-dependent crossovers, with the alpha-process shifting to higher temperatures compared to bulk water.
• The protein dynamical transition temperature coincides with the crossover of the slower relaxation.

Conclusions:

• Hydration water exhibits complex dynamics influenced by protein structure.
• Distinct relaxation processes in hydration water can be differentiated and characterized.
• Findings provide insights for interpreting experimental data on biomolecular hydration and dynamics.