Improving protein crystal quality using deep eutectic solvents

Protein crystallization is an essentially important process for its valuable applications in molecular structure determination of proteins, the study of biomolecular interaction mechanism, research and development of special functional crystal materials, theoretical study of crystallization mechanism, industrial production of proteins, and so on. Improving the quality of protein crystals is desirable research because it can provide high-quality samples or products for these studies and applications. Here we report that the utilization of DESs as additives in protein crystallization can significantly affect the crystallization process and effectively improve the crystal quality. We synthesized 9 types of DESs, studied their physicochemical properties, and selected 3 DESs suitable as additives for protein crystallization. Using three model proteins (lysozyme, thaumatin, and proteinase K), we confirmed that DESs can significantly affect the protein crystallization process. Crystals obtained at appropriate concentrations of DESs have higher quality, higher diffraction resolution, and better diffraction data collection. A comparison of the 3D structure of protein molecules showed that the addition of DESs did not affect the molecular structure of the proteins. These results proved that the presence of DESs during protein crystal-lization can help to improve crystal quality without affecting the structure of proteins, showing that DESs can be employed as a novel class of additives for protein crystallization.