Study on interaction of Ligupurpuroside A with bovine serum albumin by multi-spectroscopic methods

The interaction of Ligupurpuroside A with bovine serum albumin (BSA) has been investigated by fluorescence spectra, UV–vis absorption spectra, three-dimensional (3D) fluorescence spectra, synchronous fluorescence spectra and circular dichroism (CD) spectra along with a molecular docking method. The fluorescence experiments indicate that Ligupurpuroside A can quench the intrinsic fluorescence of BSA through a combined quenching way at the low concentration of Ligupurpuroside A, and a static quenching procedure at the high concentration. The thermodynamic analysis suggests that hydrogen bonds and van der Waals forces are the main forces between BSA and Ligupurpuroside A. According to the theory of Forster׳s non-radiation energy transfer, the binding distance between BSA and Ligupurpuroside A was calculated to be 2.73 nm, which implies that energy transfer occurs between BSA and Ligupurpuroside A. All these experimental results have been validated by the protein–ligand docking studies which show that Ligupurpuroside A binds to the residues located in the hydrophobic cavity on subdomain IIA of BSA. In addition, conformation change of BSA was observed from three-dimensional fluorescence spectra, synchronous fluorescence spectra and circular dichroism spectra under experimental conditions.