Interaction of KMP-11 and its mutants with ionic liquid choline dihydrogen phosphate: Multispectroscopic studies aided by docking and molecular dynamics simulations

Abstract

Binding interactions of KMP-11 with the IL choline dihydrogen phosphate (CDHP) solvent have been explored from multispectroscopic studies in conjunction with docking and molecular dynamics simulations. The protein KMP-11, a vaccine candidate against ‘Leishmaniasis’, does not contain any tryptophan (Trp) in its WT sequence. For this study, two single site Trp mutant proteins Y5W and Y89W of KMP -11 have been generated as Trp used as biomarker by the aid of intrinsic fluorescence. In the former mutant (Y5W) Trp is inserted in the vicinity of the N-terminal, while in the later (Y89W), the same residue is disposed near the C-terminal of the protein. The binding interactions of CDHP with both the mutant proteins have been explored from UV–Vis, steady state and time resolved fluorescence spectroscopic studies. The bimolecular quenching rate constant (kq) at various temperatures, as obtained from fluorescence spectroscopic studies suggest definite but weak binding interactions between the mutant proteins and CDHP IL solvent. This result is further corroborated from the near and far - UV Circular Dichroism (CD) spectra. The possible binding sites of CDHP in the vicinity of WT and mutant proteins and the corresponding binding forces have been predicted from the molecular docking studies. The results of MD simulation further portend minimal or no unfolding in the secondary structures of the WT and the mutant proteins upon addition of CDHP molecule. We believe that this in-depth study featuring the interaction of KMP-11 with IL CDHP will enlighten the fundamental understanding towards the development of improved protein based vaccines in general and KMP-11 guided vaccines in particular for the prevention of VL.