Temperature-dependent mechanisms for the dynamics of protein-hydration waters: a molecular dynamics simulation study

TL;DR

This study uses molecular dynamics simulations to explore how water molecules around peptides change their movement mechanisms with temperature, revealing a transition from diffusive to jump motion and identifying key energetic and structural features.

Contribution

It provides detailed insights into the temperature-dependent dynamics and structural changes of hydration water around peptides, highlighting a transition in water motion mechanisms and the role of hydrogen-bond networks.

Findings

Water dynamics shift from diffusive to jump motion upon cooling

A fragile-to-strong crossover in water behavior coincides with maximum hydrogen-bond order

Activation energy for water motion is approximately 0.43 eV

Abstract

Molecular dynamics simulations are performed to study the temperature-dependent dynamics and structures of the hydration shells of elastin-like and collagen-like peptides. For both model peptides, it is consistently observed that, upon cooling, the mechanisms for water dynamics continuously change from small-step diffusive motion to large-step jump motion, the temperature dependence of water dynamics shows a weak crossover from fragile behavior to strong behavior, and the order of the hydrogen-bond network increases. The temperature of the weak crossover from fragile to strong behavior is found to coincide with the temperature at which maximum possible order of the hydrogen-bond network is reached so that the structure becomes temperature independent. In the strong regime, the temperature dependence of water translation and rotational dynamics is characterized by an activation energy of ca. E_a=0.43 eV, consistent with results from previous dielectric spectroscopy and nuclear magnetic resonance studies on protein hydration waters. At these temperatures, a distorted pi-flip motion about the twofold molecular symmetry axes, i.e., a water-specific beta process is an important aspect of water dynamics, at least at the water-peptide interfaces. In addition, it is shown that the hydration waters exhibit pronounced dynamical heterogeneities, which can be traced back to a strong slowdown of water motion in the immediate vicinity of peptide molecules due to formation of water-peptide hydrogen bonds.