Currently buffered aqueous salt solutions are used as solvents for proteins, but these do not sufficiently control protein solubility and stability, which adversely affects protein activity, folding-unfolding transitions, aggregation and crystallisation. Therefore, there is a need for new solvents which can control protein and biomolecule solubility and stability.
Protic ionic liquids (PILs) are cost efficient “designer” solvents which can be tailored to have properties suitable for a broad range of applications [1]. These are liquid salts which are typically liquid at room temperature and miscible with water. Certain aqueous PIL solutions have beneficial properties, including stabilising biomolecules, suppressing aggregation and enhancing protein crystal growth. However, there is a lack of systematic and consistent studies, so structure-property relationships are not possible, which prevents solvent design for specific protein applications.
In this presentation I will discuss our ongoing work into designing PIL solvents for proteins, including identifying specific ionic interactions of PILs, cations and anions, with the protein surface [2]. Using Lysozyme as a model protein, we have developed and adapted characterisation methods for using proteins in PIL solutions.
Structural changes of Lysozyme, in varying concentrations of PIL, have been explored using Synchrotron small angle X-ray scattering (SAXS). The structural changes of lysozyme in solution due to the presence of PILs was quantified. Through this study we have identified regions of lysozyme structure which are most affected by the PILs. Crystallography studies were also carried out at the Synchrotron MX2 beamline. Developing PIL solvents for protein crystallisation is a key application we wish to explore. Lysozyme crystals were grown in the presence of PILs and their structures were solved. Crystallography results provided insight into which ions are present at the surface and the key amino acids ionically bonded to the PILs which is important for protein stability.