Interaction of flavokawain B with lysozyme: A photophysical and molecular simulation study

Interaction of flavokawain B (FB), a therapeutic flavonoid with lysozyme (LYZ), was studied using various spectroscopic and molecular simulation techniques. The association constant, Ka of the binding reaction was determined to be 2.79±0.16×104 M−1 at 25 °C based on fluorescence quenching titration results. Thermodynamic analysis of the binding data obtained at different temperatures along with molecular docking results suggested the involvement of hydrophobic and van der Waals forces, as well as hydrogen bonding in FB-LYZ interaction. The binding reaction between FB and LYZ was found to affect the microenvironment around protein fluorophores (Tyr and Trp) as revealed by intrinsic and three-dimensional fluorescence results. A comparison of the LYZ thermograms, obtained by far-UV CD spectroscopy in the absence and the presence of FB, suggested improved protein thermal stability upon complexation with FB. Presence of metal ions was found to affect FB-LYZ interaction. Molecular docking predicted the formation of two hydrogen bonds between the oxygen atoms of FB and amino acid residues of LYZ (Asn-59 and Trp-63), located in the vicinity of the active site, in addition to various non-polar contacts. Molecular dynamics studies showed that the complex reached equilibrium during simulation, indicating the stability of the FB-LYZ complex.