Hydration-dependent dynamic crossover phenomenon in protein hydration water

Area of Science:

• Biophysics
• Protein dynamics
• Hydration water behavior

Background:

• Protein hydration water's relaxation time (τ) is crucial for understanding protein dynamics.
• Hydration level (h) significantly influences water dynamics around proteins.

Purpose of the Study:

• To investigate the relationship between protein hydration level and water relaxation dynamics.
• To determine if hydration water dynamics directly induce protein dynamic transitions.

Main Methods:

• Analysis of characteristic relaxation time (τ) of protein hydration water.
• Observation of dynamic crossover phenomena at varying hydration levels (h).
• Measurement of Arrhenius behavior and activation energy below the monolayer hydration level (hc).

Main Results:

• Relaxation time (τ) shows strong dependence on hydration level (h).
• Dynamic crossover observed for h > hc (0.2-0.25), becoming more pronounced with increasing h.
• Arrhenius behavior observed for h < hc, with activation energy insensitive to h, suggesting local-like motion.
• Crossover temperature's dependence on h indicates protein dynamics are not solely driven by hydration water crossover.

Conclusions:

• Protein hydration water dynamics exhibit distinct behaviors above and below the monolayer hydration level.
• The observed dynamic crossover in hydration water does not solely explain the protein's dynamic transition.
• Protein dynamic transitions are influenced by factors beyond the immediate hydration water dynamics.