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

Abstract

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

HIGHLIGHTS

• Esculin causes hyperchromicity at the absorbance maxima (∼280 nm) of BSA anticipating ground state complex formation

• Fluorescence quenching of BSA in the presence of esculin indicates an alteration in the native structure of BSA.

• Synchronous fluorescence spectroscopy and circular dichroism study reveal minor microenvironment alterations and conformational change in BSA at 298.15 K.

• The binding constant (K_b) of 2.24 × 10⁴ M⁻¹ at 298.15 K confirms the moderate binding association between esculin and BSA with a single binding site

• Thermodynamic parameters suggest spontaneity in the binding of esculin with BSA, hydrogen bonding and van der Waals interaction plays a pivotal role

• The binding site of esculin on BSA is located in Sudlow’s site 1, as confirmed from site markers displacement assay

• Lys-294, Tyr-340, Val-342, Ser-343, and Trp-213 are the major residues in BSA that form a binding pocket for esculin

• Melting temperature (T_m) for BSA is increased from 65.51 °C to 70.38 °C in presence of esculin.

Keywords:

• Esculin
• bovine serum albumin
• fluorescence spectroscopy
• molecular docking
• circular dichroism

Acknowledgments

MAQ is thankful to ICMR, New Delhi, for providing SRF. All the authors are thankful to CIF, Department of Biochemistry, F/O Life Sciences, Aligarh Muslim University for providing necessary instrumentation facilities.

Author’s contribution

MAQ and MA carried out experimental work and prepared the draft manuscript, MA helped in data interpretation. SJ supervised the study and reviewed and finalized the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Funding

The author(s) reported there is no funding associated with the work featured in this article.