Probing the binding interaction of thionine with lysozyme: A spectroscopic and molecular docking investigation

• The binding interaction between TH and Lys was investigated.
• TH quenches the intrinsic fluorescence of Lys by static quenching mechanism.
• Conformational changes of Lys induced by TH complexation were observed.
• Computational studies of TH with Lys substantiate the experimental findings.

In this article, an attempt is made to explore the binding mechanism of thionine with lysozyme by using multi-spectroscopic and molecular docking methods. The results from emission and time resolved fluorescence studies revealed that the emission quenching of lysozyme with thionine is initiated by static quenching mechanism. The binding constant and number of binding site of lysozyme–thionine complex was evaluated as 4.01 × 105 dm3 mol−1 and ≈1, respectively. Furthermore, the results from absorption, constant wavelength synchronous fluorescence, three dimensional emission and circular dichroism spectral studies showed that thionine induced conformational changes in the secondary structure of lysozyme. Molecular docking study confirmed that the probable binding site of thionine is located near trptophan-63 residue of lysozyme and it is further revealed that the existence of hydrogen bonding along with hydrophobic interaction are the primary forces responsible for the complexation of thionine with lysozyme.

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