Unveiling the Influence of Hydrated Deep Eutectic Solvents on the Dynamics of Water–Soluble Proteins

Deep eutectic solvents (DESs) are mixtures of two ormore purecompounds (e.g., Lewis or Bronsted acids and bases, anionic and/orcationic species) in a well-defined stoichiometric proportion, witha melting point lower to that of an ideal liquid mixture. These neotericsolvents are highly tunable through varying the structure or relativeratio of parent components and have been evaluated as solvents ableto improve biomolecules' performance, specifically their stabilityand biocatalytic properties. Inspired by a recent crystallographicstudy, we have explored through molecular dynamics (MD) simulationsthe dynamic properties of two different proteins (hen egg-white lysozymeand the human VH antibody fragment HEL4) in a (20% w/w) hydrated solutionof choline chloride-glycerol (1:2). We have developed properforce fields to account for DES, protein, and DES-protein interactions,which have been calibrated using pair distribution function measurementsof pure DES solutions. MD results show that the presence of DES quenchesthe protein motion, increasing the rigidity of the overall proteinstructure. Specific interactions among DES components and proteinresidues, such as those between choline ions and two Tryptophan residuesof lysozyme, may amplify the protein-DES interactions and leadto protein crystallization in the presence of hydrated DES. Thesefindings open new horizons to improve or achieve control on proteinproperties by a proper choice of hydrated DESs used as solvents.