Electrostatic fluctuations promote the dynamical transition in proteins

TL;DR

This paper investigates how electrostatic fluctuations influence the dynamical transition in proteins, linking dielectric response to atomic motion changes through a model that explains experimental observations.

Contribution

It introduces a model analyzing electrostatic fluctuations and viscoelastic effects as mechanisms driving the protein dynamical transition, supported by experimental data interpretation.

Findings

Electrostatic fluctuations dominate high-temperature atomic flexibility.

Two distinct onsets in mean square displacements linked to different relaxation mechanisms.

Model explains temperature-dependent protein atomic motion changes.

Abstract

Atomic displacements of hydrated proteins are dominated by phonon vibrations at low temperatures and by dissipative large-amplitude motions at high temperatures. A crossover between the two regimes is known as a dynamical transition. Recent experiments indicate a connection between the dynamical transition and the dielectric response of the hydrated protein. We analyze two mechanisms of the coupling between the protein atomic motions and the protein-water interface. The first mechanism considers viscoelastic changes in the global shape of the protein plasticized by its coupling to the hydration shell. The second mechanism involves modulations of the motions of partial charges inside the protein by electrostatic fluctuations. The model is used to analyze mean square displacements of iron of metmyoglobin reported by Moessbauer spectroscopy. We show that high flexibility of heme iron at physiological temperatures is dominated by electrostatic fluctuations. Two onsets, one arising from the viscoelastic response and the second from electrostatic fluctuations, are seen in the temperature dependence of the mean square displacements when the corresponding relaxation times enter the instrumental resolution window.