Sugars have received a huge interest over the past few decades for their preservation capabilities of biosystems such as cells, vaccines, or therapeutic proteins employed in the pharmaceutical industries. Indeed, disaccharides  can be added to biologically active solutions to overcome the limited stability range of proteins (pH, temperature,...). These additives prevent the partial or even total degradation of biomolecules due to the lethal thermal or dehydration stresses encountered during industrial conservation methods (lyophilization). However, the molecular mechanisms at the origin of the  biopreservation phenomenon itself still remain unclear. Several hypotheses (glass transition temperature, water molecules replacement, hydrogen bonding destructuring effect, preferential excluded volume,…) have been proposed, but none of them can be considered as fully accepted.
In order to better understand the physical properties of sugars and their influence on the protein stability we have performed Molecular Dynamics investigations of hen egg-white lysozyme in presence of three homologous disaccharides: trehalose, sucrose and maltose. This study shows that the hydrogen bonds network of water is highly dependent on the presence of sugars and contributes to the stabilization of lysozyme. The privileged interaction of trehalose with water is confirmed below a threshold weight sugar concentration. Above this concentration, trehalose becomes less efficient to distort the tetra-bonded HB network of water than maltose. This result is interpreted as a competition between sugars and lysozyme to bind to water molecules. At high sugar concentration, trehalose molecules are found less capable to perturb water molecules which bind preferentially to lysozyme consistently with the preferential hydration hypothesis. The analysis of the relative concentration of water oxygen atoms around lysozyme suggests that lysozyme is preferentially hydrated.

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