Exploring the binding interactions of janus green blue with serum albumins from spectroscopic and calorimetric studies aided by in silico calculations

Abstract

Binding interactions of the phenazinium dye Janus green blue (JGB) with human and bovine serum albumins (BSA – and BSA) have been explored for the first time from multi-spectroscopic and calorimetric measurements aided by in silico calculations. The formation of ground state complexes between JGB and the respective serum albumins have been suggested from the UV–Vis and steady-state fluorescence spectroscopic studies. The nonlinear Stern Volmer (SV) plots at higher concentrations of JGB primarily indicate the formation of more than one ground state complexes in BSA –/BSA–JGB systems. Modified SV plots and isothermal titration calorimetry (ITC) studies however signify the possibilities of one type of binding complexes between HSA/BSA – JGB systems. Binding constants and the thermodynamic parameters associated with the HSA/BSA–JGB complexes have also been estimated from the ITC studies. Förster distances (R0 ) for HSA–JGB and BSA–JGB complexes are estimated from Förster resonance energy transfer (FRET) results. Variations in the micro-environment of the Tyr and Trp residues of the serum proteins in presence of JGB have been observed from the synchronous fluorescence measurements. The conformational changes in the protein structures induced by the dye JGB have been revealed from 3 D fluorescence and circular dichroism (CD) studies. The experimental observations are supported by in silico calculations. This in depth investigation on the interactions of serum albumins with JGB may provide the fundamental information toward exploring the therapeutic efficacy of JGB as a potent drug molecule. Communicated by Ramaswamy H. Sarma