Effects of Ionic Liquids as Additives on Protein Crystallization

Protein crystallization is a complex process, where every component and physical parameter of the crystallization process may have an effect on the outcome. Crystallization conditions are typically arrived at by a screening process, where the target is subjected to a broad array of solution conditions with the goal of obtaining at least one condition that can be carried on to a structure. Ionic liquids (IL) have been found to be useful additives for improving the outcomes of the crystallization process, with existing data indicating that the IL structure has an effect. We describe a method for quickly preparing a series of solutions that vary in just one component, in this case a series of ILs that are used as crystallization additives. The method results in a screening grid, where the crystallization conditions being tested are constant in any one column in the Y dimension and they ILs are constant in any one row in the X dimension. This provides a systematic approach to determining effective ILs for obtaining crystals from a limited set of promising starting crystallization conditions. The approach generates an X-Y array of conditions, where the basic precipitant conditions are kept constant in one plate dimension and the additives are kept constant in the second dimension, generating a 12 × 8 array of conditions. This approach would also be useful for surveying other classes of protein crystallization additives in a systematic fashion.