Effects of Ionic Liquids on HP35 Folding Thermodynamics

Ionic liquids (ILs) are a class of solvents comprised of salts that are liquid below 100°C. ILs have been shown to affect the structure and function of many proteins and enzymes. The magnitude and nature of these effects varies from protein to protein and from IL to IL. Molecular simulations can be employed to better understand the ways in which ILs interact with proteins. In this study, we measure the effects of IL-water mixtures on the the folding thermodynamics of a model protein (HP35) using microcalorimetry experiments and simulations utilizing parallel tempering metadynamics in the well-tempered ensemble. These simulations quickly elucidate the free energy and entropy of unfolding for HP35. Furthermore, the results of the simulations can be reweighed to project the free energy onto any collective variable of choice. These methods can be used to better understand detailed interactions of a protein with ILs or to reparametrize force fields to more accurately reproduce thermodynamic observables.