Binding interactions between prazosin and α1A-adrenoceptor: investigation on the thermodynamic behaviors and the binding mechanism by high performance affinity chromatography

Abstract

Although the association constant and the number of binding sites of prazosin to α_1A-adrenoceptor were determined by high performance affinity chromatography (HPAC) in our previous work, the thermodynamic behaviors and the binding mechanism of the drug to immobilized α_1A-adrenoceptor remained unclear. This work intended to address the issue by HPAC and molecular docking. The investigations involved the determination of association constants by frontal analysis at different temperatures, the calculation of enthalpy, entropy and free energy changes, the examination of mobile phase composition on the binding parameters and the site-directed molecular docking. The changes of enthalpy, entropy and free energy during the interaction were −20.79 kJ mol⁻¹, −59.28 J mol⁻¹ K⁻¹ and −2.4 kJ mol⁻¹, respectively. The binding of prazosin to α_1A-adrenoceptor was an endothermic process with an increase in entropy. This reaction was mainly driven by hydrogen bonds. The ionic strength of the mobile phase provided a positive response to the values of association constants, while the power of hydrogen and the concentration of isopropyl in the mobile phase showed a negative trend. Ser²⁰³ and Ser¹⁹² in the fifth transmembrane segment of the receptor were the positions for the formation of hydrogen bonds. It is possible to utilize the immobilized receptor to determine the mechanism of drug–receptor interactions.