The Effect of Ionic Liquids on Protein Crystallization and X-ray Diffraction Resolution

Ionic liquidsexhibit a variety of properties that make them attractive solvents for biomaterials. Given the potential for productive interaction between ionic liquidsand biological macromolecules, we investigated the use of ionic liquidsas precipitating agents and additives for protein crystallizationfor six model proteins (lysozyme, catalase, myoglobin, trypsin, glucose isomerase, and xylanase). The ionic liquidsproduced changes in crystal morphology and mediated significant increases in crystal size in some cases. Crystals grown using ionic liquidsas precipitating agents or as additives provided X-ray diffraction resolution similar to or better than that obtained without ionic liquids. Based upon the experiments performed with model proteins, the ionic liquidswere used as additives for the crystallization of the poorly diffracting monoclonal antibody 106.3 Fab in complex with the B-type natriuretic peptide (5-13). The ionic liquidsimproved the crystallization behavior and provided improved diffraction resulting in the determination of the structure. Ionic liquidsshould be considered as useful additives for the crystallization of other proteins.