Structural Stability of Proteins in deep Eutectic Solvents and their Aqueous Solutions

Abstract

Deep Eutectic Solvents (DESs) are eutectic mixtures composed of different cations and anions of Lewis and Bronsted acids and bases. With their favorable properties such as low volatility, biodegradability, low cost, simple synthesis, etc., they are considered as green media and sustainable replacements of ionic liquids (1). One amongst many promising applications of DESs is maintaining the structure of protein in the absence of water. Experimental studies conducted on different proteins in DESs and their aqueous solutions have shown that the secondary and most of the tertiary protein structure is maintained in the DESs and that refolding can also be achieved in aqueous DESs (2, 3). However, the experiments are limited and the intermolecular interactions between the solvents and protein are obscured. To this end, we perform molecular dynamics simulations of lysozyme in its native structure in the presence of DES composed of urea and choline chloride, known as Reline, and its aqueous solutions. The simulations are carried to analyze (i) protein structure at room temperature, (ii) protein structure at high temperatures, when unfolding occurs and (iii) refolding of thermally unfolded protein structure at room temperature in reline and its aqueous solutions.