Investigation of the molecular interaction between apraclonidine, an α2-adrenergic receptor agonist, and bovine serum albumin using fluorescence and molecular docking techniques

Apraclonidine (APR) is a potent and selective α2-adrenergic receptor agonist used in the diagnosis of Horner’s Syndrome, and the residuals of APR that accumulate in tissues of animals can cause central nervous and cardiovascular systems influences in humans. Therefore, to understand the influence of APR on human health, we examined the interaction of APR with the carrier protein in plasma, bovine serum albumin (BSA). The BSA fluorescence signal was quenched due to the APU–BSA complex formation and a weak binding affinity was estimated between APR and BSA. The inclusion of fluorescence, UV–vis absorption, molecular docking, and dynamics simulation techniques employed to broadly investigate the combination of APR with BSA at typical physiological conditions. The thermodynamic results revealed that enthalpy (ΔH⁰) and entropy (ΔS⁰) changes were computed as +11.14 kJ mol⁻¹ and +97.56 J mol⁻¹ K⁻¹, respectively, which represented the binding is principally entropy-driven and the hydrophobic forces acting a significant role in the reaction. Analysis of synchronous and 3-D fluorescence signals revealed microenvironmental variations close to BSA’s Trp and Tyr residues upon APR addition. Both the competitive site marker as well as molecular docking results detected that APR exhibited a stronger binding affinity towards Drug Site 2 (DS2) compared to Drug Site 1 (DS1).