The binding selectivity of quercetin and its structure-related polyphenols to human serum albumin using a fluorescent dye cocktail for multiplex drug-site mapping

Human serum albumin (HSA) is a serum protein that carries flavonoids in blood circulation. In this report, the binding selectivity and strength of interactions to HSA-binding sites (sites I or II) by flavonoids were evaluated using competition experiments and the specific fluorescent dyes, dansylamide and BD140. Most tested flavonoids bound site I preferentially, with the binding strength dependent on the mother structure in the order flavonol > flavone > flavanone > flavan 3-ols. Glycosylation or glucuronidation reduced the binding of quercetin to site I of HSA, whereas sulfation increased binding. Quercetin 7-sulfate showed the strongest binding and molecular docking simulations supported this observation. Prenylation at any position or glucuronidation and sulfation at the C-4 ' or C-7 position of quercetin facilitated stronger binding to site II. The binding affinity of flavonoids toward site I correlated with the partition coefficient value (logP), whereas no corresponding correlation was observed for site II.