Insight into impact of choline-based ionic liquids on bovine β-lactoglobulin structural analysis: Unexpected high thermal stability of protein

In this present work, we report the effects of different concentrations of various cholinium-based ionic liquids (ILs) on the structural and thermal stability of beta-lactoglobulin (beta-LG). Results indicated that anions in ILs have played an important role in affecting the thermal and structural stability of beta-LG. Biomolecular interactions between beta-LG and ILs are carried out by differential scanning calorimetry (DSC), different spectroscopic and dynamic light scattering (DLS). Analysis of experimental data revealed that an excellent thermal stability of beta-LG is obtained in presence of choline dihydrogen phosphate [Chn][Dhp] and choline bitartrate [Chn][Bit] where T-m value of beta-LG increased to 93.58 and 93.22 degrees C, respectively, as compared to T-m of beta-LG in buffer at 72.48 degrees C. Similarly, in presence of choline acetate [Chn][Ac] and choline chloride [ChnJ[Cl] thermal stability of beta-LG also increased, however, it was not possible to calculate T-m values in case of choline iodide [Chn][1], because of obtaining two endothermic peaks in DSC curves. On the other hand, choline hydroxide [Chn][OH] acts as complete destabilizer for beta-LG native structure as no T-m is obtained in its presence. The obtained results are further confirmed by estimating the thermodynamic parameters such as Gibbs free energy of unfolding (Delta(u)G), enthalpy of unfolding (Delta H-u), heat capacity change (Delta Cp) and total entropy change during protein unfolding (Delta S-u ). Molecular docking studies of beta-LG and various choline-based ILs are also performed to know the probable binding conformations using AutoDock Vina and AutoDock tools 1.5.6, results obtained are in correlation with spectroscopic and biothermodynamic data. The combined study by DSC, spectroscopy techniques and molecular docking studies suggest that some of these ILs can be used as industrial green solvents for different biocatalytic processes and also can help in resolving the problems involving protein unfolding and thermal stability studies. (C) 2018 Elsevier B.V. All rights reserved.