Evidence Of Protein Collective Motions On The Picosecond Time Scale

TL;DR

This study combines terahertz spectroscopy and molecular dynamics to reveal protein collective motions on a picosecond scale, showing how oxidation and hydration influence these motions in cytochrome c.

Contribution

It provides new evidence linking collective protein motions to oxidation state and hydration level, using combined experimental and simulation approaches.

Findings

THz response increases with oxidation and hydration

Collective mode density of states explains hydration dependence

Dipole-dipole correlation functions reveal diffusive motions related to oxidation

Abstract

We investigate the presence of structural collective motions on a picosecond time scale for the heme protein, cytochrome c, as a function of oxidation and hydration, using terahertz (THz) time-domain spectroscopy and molecular dynamics simulations. The THz response dramatically increases with oxidation, with the largest increase for lowest hydrations and highest frequencies. For both oxidation states the THz response rapidly increases with hydration saturating above ~25% (g H2O/g protein). Quasi-harmonic vibrational modes and dipole-dipole correlation functions are calculated from molecular dynamics trajectories. The collective mode density of states alone reproduces the measured hydration dependence providing strong evidence of the existence of these motions. The large oxidation dependence is reproduced only by the dipole-dipole correlation function, indicating the contrast arises from diffusive motions consistent with structural changes occurring in the vicinity of a buried internal water molecule.