Ionic liquids (ILs) have been recently utilized in numerous biochemistry applications, including in biomass solubilization, enzymology, and the development of antibacterial drugs. A current area of research is in understanding the effects of ILs in aqueous solutions on the structures and stabilities of biomolecules, including proteins. Many ILs affect protein unfolding thermodynamics and kinetics, but the mechanisms through which ILs alter protein unfolding can depend on specific IL cation/anion combinations. We investigated the effects of aqueous BMIBF4 and EMIAc ILs on myoglobin unfolding in urea. Both ILs destabilize the protein structure, as reflected in decreased ΔGunfolding values. Unfolding kinetics experiments show that first-order unfolding rate constants increase linearly with increasing IL concentration. In agreement with previous thermodynamic results, the kinetic effects are more pronounced with BMIBF4, which suggests that the IL interacts strongly with the myoglobin protein during the unfolding process. This hypothesis is verified by ESI-MS experiments that demonstrate formation of protein-BF4- complexes. The effects of the ILs on the protein structures were quantified by hydrogen-deuterium exchange (HDX) experiments, which suggest that the protein may adopt a less tightly-packed structure (relative to native protein) in the presence of the BMIBF4.

Differences in protein unfolding mechanisms revealed characterized in aqueous ionic liquid solutions

249th National Meeting (2015)

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