Structural insights into the binding behavior of isoflavonoid glabridin with human serum albumin

Glabridin (GB), a prenylated isoflavonoid in licorice root has been used as foods and medicines with beneficial biological activities. Human serum albumin (HSA) is the most abundant blood plasma protein binding and transporting ligands such as GB. The present study investigated the interaction between GB and HSA using multi-spectroscopic and molecular docking techniques. Fluorescence spectroscopy demonstrated that GB strongly quenched the tryptophan fluorescence emission of HSA, suggesting that GB-HSA interaction followed a static mode of quenching with a binding constant (K, 10(5) -10(4) M-1, 25-37 degrees C) reflecting strong-to-moderate affinity of GB to HSA. Molecular displacement and protein-ligand docking simulations showed that the probable GB-binding positions of HSA exist near the site I of HSA. The hydrophobic interaction is a dominant binding force for forming GB-HSA complexes, and the binding resulted in conformational changes of HSA protein with more beta-sheet structures. Furthermore, the complex formation of GB with HSA changed the hydrodynamic size and zeta-potential of HSA with enhanced solubility of GB. The elucidation of GB-HSA binding behavior will provide insights into the application of GB in food and pharmaceutical industries.