Dynamics of cytochrome c in surface active ionic liquid: A study of preferential interactions towards denaturation

Surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium octyl sulfate ([C(4)mim][C8OSO3]) having octyl tail on anionic moiety have been very less investigated with proteins. Herein, we present a study of the structural change of horse heart cytochrome c (h-cyt c) in aqueous solutions of SAIL ([C(4)mim][C8OSO3]) by optical spectroscopy and molecular docking methods. Time-resolved fluorescence, UV-vis and circular dichroism (CD) spectra indicated that the addition of up to 25 mM of [C(4)mim][C8OSO3] induces structural changes of h-cyt c resulting from disruption of tertiary structure and after 25 mM of [C(4)mim][C8OSO3], h-cyt c denatures completely and loses its tertiary structure. Thermodynamic parameters for denaturation of h-cyt c by [C(4)mim][C8OSO3] were also obtained having Delta G degrees(D) and m-value of the unfolded state. The values were found to be lower when compared to the reported for urea denatured h-cyt c. The midpoint concentration of unfolding of h-cyt c by [C(4)mim] [C8OSO3] was found similar to 25 mM. The results showed that the presence of alkyl chain on the anionic moiety destabilizes the protein. The docking results confirm the preferential interactions of ions of SAIL to residues of h-cyt c and suggest the dominant role of anion [C8OSO3](-) by the electrostatic interaction that drives local destabilization of the h-cyt c. (C) 2018 Elsevier B.V. All rights reserved.