An insight into the binding of 6-hydroxyflavone with hen egg white lysozyme: a combined approach of...

The interaction of 6-hydroxyflavone (6HF) with hen egg white lysozyme (HEWL) has been executed using multi-spectroscopic and computational methods. Steady state fluorescence studies indicated that static quenching mechanism is involved in the binding of 6HF with HEWL, which was further supported by excited state lifetime and UV-vis absorption studies. The binding constant (K_b) of the HEWL-6HF complex was observed to be 6.44 ± 0.09 × 10⁴ M^-1 at 293 K, which decreases with the increase in temperature. The calculation of the thermodynamic quantities showed that the binding is exothermic in nature with a negative enthalpy change (ΔH = -11.91 ± 1.02 kJ mol^-1) along with a positive entropy change (ΔS = +51.36 ± 2.43 J K^-1 mol^-1), and the major forces responsible for the binding are hydrogen bonding and hydrophobic interactions. The possibility of energy transfer from tryptophan (Trp) residue to the 6HF ligand was observed from Fo¨rster's theory. The inclusion of 6HF within the binding site of HEWL induces some micro-environmental changes around the Trp residues as indicated by synchronous and three-dimensional (3D) fluorescence studies. The changes in secondary structural components of HEWL are observed on binding with 6HF along with a reduction in % α-helical content. Computational studies correlate well with the experimental finding, and the ligand 6HF is found to bind near to Trp 62 and Trp 63 residues of HEWL. Altogether, the present study provides an insight into the interaction dynamics and energetics of the binding of 6HF to HEWL. Communicated by Ramaswamy H. Sarma.