Molecular packing, hydrogen bonding, and fast dynamics in lysozyme/trehalose/glycerol and trehalose/glycerol glasses at low hydration

TL;DR

This study uses molecular dynamics simulations to explore how water and glycerol influence the molecular packing, hydrogen bonding, and fast dynamics of lysozyme/trehalose/glycerol glasses at low hydration, revealing their complex roles in protein stability.

Contribution

It provides detailed insights into how water and glycerol modulate fast protein and sugar dynamics and hydrogen bonding in glassy matrices, advancing understanding of stabilization mechanisms.

Findings

Glycerol and water decrease the glass transition temperature of the mixtures.

They improve molecular packing in the glasses.

Water and glycerol can antiplasticize fast dynamics by increasing hydrogen bonds.

Abstract

Water and glycerol are well-known to facilitate the structural relaxation of amorphous protein matrices. However, several studies evidenced that they may also limit fast ($\sim$ pico-nanosecond, ps-ns) and small-amplitude ($\sim$ \AA ) motions of proteins, which govern their stability in freeze-dried sugar mixtures. To determine how they interact with proteins and sugars in glassy matrices and, thereby, modulate their fast dynamics, we performed molecular dynamics (MD) simulations of lysozyme/trehalose/glycerol (LTG) and trehalose/glycerol (TG) mixtures at low glycerol and water concentrations. Upon addition of glycerol and/or water, the glass transition temperature, T$_{\textrm{g}}$, of LTG and TG mixtures decreases, the molecular packing of glasses is improved, and the mean-square displacements (MSDs) of lysozyme and trehalose either decrease or increase, depending on the time scale and on the temperature considered. A detailed analysis of the hydrogen bonds (HBs) formed between species reveals that water and glycerol may antiplasticize the fast dynamics of lysozyme and trehalose by increasing the total number and/or the strength of the HBs they form in glassy matrices.