How does the first water shell fold proteins so fast ?

TL;DR

This study investigates how water's hydrogen bonding in the first hydration shell influences protein folding speed, revealing a double-funnel mechanism with rapid folding pathways above the glass transition temperature.

Contribution

It introduces a theoretical hydration model and statistical physics approach to explain the role of water in protein folding dynamics, highlighting the importance of hydrogen bonds in folding pathways.

Findings

Rapid folding occurs via pathways with broken hydrogen bonds above the glass transition.

Folding follows a double-funnel mechanism with distinct temperature-dependent pathways.

Hydrogen bond formation dominates at low temperatures with slow conformational changes.

Abstract

First shells of hydration and bulk solvent plays a crucial role in the folding of proteins. Here, the role of water in the dynamics of proteins has been investigated using a theoretical protein-solvent model and a statistical physics approach. We formulate a hydration model where the hydrogen bonds between water molecules pertaining to the first shell of the protein conformation may be either mainly formed or broken. At thermal equilibrium, hydrogen bonds are formed at low temperature and are broken at high temperature. To explore the solvent effect, we follow the folding of a large sampling of protein chains, using a master-equation evolution. The dynamics shows a clear mechanism. Above the glass-transition temperature, a large ratio of chains fold very rapidly into the native structure irrespective of the temperature, following pathways of high transition rates through structures surrounded by the solvent with broken hydrogen bonds. Although these states have an infinitesimal probability, they act as strong dynamical attractors and fast folding proceeds along these routes rather than pathways with small transition rates between configurations of much higher equilibrium probabilities. At a given low temperature, a broad jump in the folding times is observed. Below this glass temperature, the pathways where hydrogen bonds are mainly formed become those of highest rates although with conformational changes of huge relaxation times. The present results reveal that folding obeys a double-funnel mechanism.