Potential of a Natural Deep Eutectic Solvent, Glyceline, in the Thermal Stability of the Trp-Cage Mini-protein.

Deep eutectic solvents (DESs) are the new class of green and inexpensive anhydrous solvents, which are alternatives of ionic liquids. The applications of these promising anhydrous sustainable solvents in biological media have been explored. However, the behavior and stability of biomolecules in DES are not clearly understood. In this study, we have investigated the stability of Trp-cage mini-protein in glyceline, which is a natural deep eutectic mixture (NADES) of choline chloride and glycerol. A series of all-atom molecular dynamics at different temperatures are carried out, and it is found that the protein is stable at much higher temperatures in a DES solvent than in water medium. It is observed that at 400 K this protein denatures from its native state in water medium whereas it retains its native structure up to 400 K temperature in DES medium. Through various analyses, it is also noticed that the interaction between the protein and the glycerol and the choline molecules decreases with the increase in temperature from 300 to 400 K. The crucial parameters, which help in the stabilization of the folded conformation of Trp-cage mini-protein, are maintained in glyceline up to a temperature of 400 K, but they disintegrate at 450 K. The low diffusion coefficient of the glyceline molecules helps to maintain the folded conformation of Trp-cage, which increases at high temperature, causing distortion in the stable interactions between the mini-protein and the solvent molecules. This ultimately leads to the unfolding of the mini-protein. Since Trp-cage mini-protein is a prototypical protein, the thermal stability of this protein in this NADES proves this solvent as an ideal medium for biocatalytic reactions and long-time storage of biomolecules.