Spectroscopic and molecular modeling approaches to investigate the binding of proton pump inhibitors to human serum albumin

Abstract

The interaction between two proton pump inhibitors viz., omeprazole (OME) and esomeprazole (EPZ) with human serum albumin (HSA) was studied by fluorescence, absorption, circular dichroism (CD), Fourier transform infrared spectroscopy (FT-IR), voltammetry, and molecular modeling approaches. The Stern–Volmer quenching constants (K_sv) for OME-HSA and EPZ-HSA systems obtained at different temperatures revealed that both OME and EPZ quenched the intensity of HSA through dynamic mode of quenching mechanism. The binding constants of OME-HSA and EPZ-HSA increased with temperature, indicating the increased stability of these systems at higher temperatures. Thermodynamic parameters viz., ∆H^°, ∆S^°, and ∆G^° were determined for both systems. These values revealed that both systems were stabilized by hydrophobic forces. The competitive displacement and molecular docking studies suggested that OME/EPZ was bound to Sudlow’s site I in subdomain IIA in HSA. The extent of energy transfer from HSA to OME/EPZ and the distance of separation in tryptophan (Trp214) Trp214-OME and Trp214-EPZ was determined based on the theory of fluorescence resonance energy transfer. UV absorption, 3D fluorescence, and CD studies indicated that the binding of OME/EPZ to HSA has induced micro environmental changes around the protein which resulted changes in its secondary structure.

Keywords:

• HSA
• omeprazole
• esomeprazole
• fluorometry
• circular dichroism
• molecular docking

Acknowledgements

The authors thank the University Grant Commission, New Delhi, for providing the financial support to carry out this work [F.No 43-205/2014(SR) dated 18-08-2015]. Thanks are due to the Chairman, Department of Molecular Biophysics, Indian Institute of Science, Bangalore, for CD facilities. One of the authors (Suma K Pawar) acknowledges the University Grant Commission, New Delhi, for awarding the Rajiv Gandhi National Fellowship (F1-17.1/2016-17/RGNF-2015-17-SC-KAR-11858 dated January 2016).

Disclosure statement

No potential conflict of interest was reported by the authors.