Investigation of the interaction between bromocriptine and human serum albumin with spectroscopic techniques and computational approaches

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Fluorescence and absorption spectroscopy coupled with molecular docking techniques were chosen to reveal the molecular relationship between bromocriptine (BRC), a dopamine agonist, and human serum albumin (HSA), the major carrier protein in the bloodstream. The gradual decrease of Stern-Volmer constant (KSV) with increasing temperatures noted that BRC induced quenching in HSA fluorescence occurred via a static quenching mechanism, thus indicating the formation of complexes between BRC and HSA. The changes observed in the UV-vis absorption spectra of HSA as a result of BRC addition and the fact that the biomolecular quenching rate constants (Kq) calculated for the BRC-HSA interaction are significantly larger than the highest value of the dynamic quenching rate constant also support this conclusion. Considering the experimentally obtained binding constant (Ka) values ​​(2.6 − 3.8 x 104 M−1), BRC appeared to bind to HSA with a moderate affinity. Analysis of thermodynamic data suggested the association of hydrophobic interactions, H-bonds and van der Waals forces as the main interaction forces in the BRC–HSA binding. It was determined by 3-D fluorescence spectra that the binding of BRC to the protein led to significant changes in the Tyr/Trp microenvironment of the protein. Docking analyses and drug displacement experiments identified that BRC likely binds to subdomain IIA (Site I) of HSA.