Batch crystallization of soluble proteins: effect of precipitant, temperature and additive

Although techniques used for protein crystallization have been progressing greatly, successful crystallization is still largely empirical and operatordependent. The crystallization of biological macromolecules is a pretty complicated process involving numerous parameters, thus the detailed understanding of the effect of crystallization conditions on macromolecule crystallization is advantageous. In this study, we have investigated the effect of precipitant, temperature, and additive on the crystallization of lysozyme and chymotrypsinogen A. As the precipitant, sodium chloride is more effective to the crystallization of lysozyme, and ammonium sulfate is more suitable to the crystallization of chymotrypsinogen A. Temperature is found to have no effect on the crystal habit of chymotrypsinogen A, while lysozyme crystallization displays highly sensitive temperature dependence, gradually varied temperature can result in better crystal habit and quality of lysozyme crystals. Furthermore, non-electrolytic additives dimethyl sulfoxide (DMSO) and glycerol are found to not only to increase the protein's solubility, but also decrease the critical supersaturation S_c for explosive nucleation of highly supersaturated protein solution. It is suggested that these additives can affect the interactions between protein molecules, thermodynamic equilibrium, surface energy of the crystal, and nucleation process of protein crystallization.