# Dynamical coupling between protein conformational fluctuation and hydration water: Heterogeneous dynamics of biological water

## TL;DR

This study explores how protein side-chain fluctuations influence hydration water dynamics, revealing heterogeneous relaxation timescales and anti-correlated energy flow between protein core, side-chains, and water molecules.

## Contribution

It provides new insights into the coupling mechanisms between protein conformational fluctuations and hydration water dynamics, emphasizing the role of side-chain motions.

## Key findings

- Different residues show distinct relaxation timescales.
- Anti cross-correlations indicate energy flow between protein and water.
- Side-chain fluctuations significantly affect solvation dynamics.

## Abstract

We investigate dynamical coupling between water and amino acid side-chain residues in solvation dynamics by selecting residues often used as natural probes, namely tryptophan, tyrosine and histidine, located at different positions on protein surface and having various degrees of solvent exposure. Such differently placed residues are found to exhibit different timescales of relaxation. The total solvation response, as measured by the probe is decomposed in terms of its interactions with (i) protein core, (ii) side-chain atoms and (iii) water molecules. Significant anti cross-correlations among these contributions are observed as a result of side-chain assisted energy flow between protein core and hydration layer, which is important for the proper functionality of a protein. It is also observed that there are rotationally faster as well as slower water molecules than that of bulk solvent, which are considered to be responsible for the multitude of timescales that are observed in solvation dynamics. We also establish that slow solvation derives a significant contribution from protein side-chain fluctuations. When the motion of the protein side-chains is forcefully quenched, solvation either becomes faster or slower depending on the location of the probe.