Molecular interactions of esculin with bovine serum albumin and recognition of binding sites with spectroscopy and molecular docking

Esculin is structurally a hydroxycoumarin found in various medicinal plants. This study investigates the binding mode of esculin with bovine serum albumin by employing numerous spectroscopic studies and molecular docking approaches. Ultraviolet absorption spectroscopy revealed ground state complex formation between esculin and bovine serum albumin. At the same time, steady-state fluorescence studies showed quenching in the fluorescence emission spectra of BSA in the presence of esculin. To get insight into the location of the binding pocket of esculin on BSA, warfarin and ibuprofen site markers were used. Competitive site marker displacement assay revealed that esculin binds to Sudlow's site I (subdomain IIA) in bovine serum albumin. Thermodynamic parameters suggested that hydrogen bonding and van der Waals interaction stabilizes the esculin-BSA complex. Förster's non-radiation energy transfer analysis described the high propensity of energy transfer between bovine serum albumin and esculin. The molecular docking approach facilitated locating the binding pocket, amino acid residues involved, types of interacting forces, and binding energy (ΔG) between esculin and BSA. Circular dichroism revealed the effect of the binding of esculin on the secondary structure and helped understand the thermal unfolding profile of BSA in the presence of esculin.Communicated by Ramaswamy H. Sarm.