Dynamical transition, hydrophobic interface, and the temperature dependence of electrostatic fluctuations in proteins

TL;DR

This study uses molecular dynamics simulations to explore how temperature influences electrostatic fluctuations at protein active sites, highlighting a transition linked to water interface dynamics and solvent properties.

Contribution

It uncovers the temperature-dependent behavior of electrostatic fluctuations and identifies a transition related to the hydrophobic interface and water's Widom line crossing.

Findings

Electrostatic fluctuation amplitude increases with temperature.

A spike at 220 K indicates a transition in water-protein interactions.

Slowing of dynamics at 220 K correlates with crossing the Widom line.

Abstract

Molecular dynamics simulations have revealed a dramatic increase, with increasing temperature, of the amplitude of electrostatic fluctuations caused by water at the active site of metalloprotein plastocyanin. The increased breadth of electrostatic fluctuations, expressed in terms of the reorganization energy of changing the redox state of the protein, is related to the formation of the hydrophobic protein/water interface allowing large-amplitude collective fluctuations of the water density in the protein's first solvation shell. On the top of the monotonic increase of the reorganization energy with increasing temperature, we have observed a spike at 220 K also accompanied by a significant slowing of the exponential collective Stokes shift dynamics. In contrast to the local density fluctuations of the hydration-shell waters, these spikes might be related to the global property of the water solvent crossing the Widom line.