Deep eutectic solvents for the preservation of concentrated proteins: the case of lysozyme in 1 : 2 choline chloride : glycerol

Abstract

The stability and activity of a model protein, lysozyme, in 1 : 2 choline chloride : glycerol was characterised across a wide range of protein concentrations, i.e., between 4 and 143 mg ml⁻¹, where the protein is soluble and physically stable. Lysozyme folds into a globular conformation in this deep eutectic solvent like that in the native state, but with subtle variations in its internal structure. The protein remained stable even after 40 days of storage at room temperature and retrieved its native conformation and activity upon rehydration. These results show the potential of deep eutectic solvents as sustainable, non-toxic, and synthetically accessible media for the storage and preservation of proteins in a concentrated regime without the requirement of other excipients.