Supramolecular Control of Protein Secondary Structure Recovery by Host–Guest Complexation of Ionic Liquids with β-Cyclodextrin

Protein refolding and unfolding assays are essential for understanding of protein conformational transitions, assessing the stability of proteins, particularly their acclimatization into various environmental conditions, and for deeper insights into the mechanisms of diseases and therapeutic treatment. Ionic liquids (ILs) are a common adduct in protein folding assays as they help solubilize and stabilize proteins. Here, we describe the "IL-supramolecular host-guest complexation" with β-cyclodextrin (β-CD) and the effect of β-CD on protein unfolding and refolding using the assistance of ILs. Isothermal titration calorimetry (ITC) was employed to demonstrate IL binding, whereas fluorescence titrations and NMR experiments were used to determine the host-guest complex conformations. Thermal denaturation and renaturation experiments showed that β-CD reversed the IL-stabilizing influence in these experiments providing a new technique for demonstrating a supramolecular strategy to regulate protein folding through controlled modulation of ionic liquid-protein interactions.