Interaction behavior between five flavonoids and pepsin: Spectroscopic analysis and molecular docking

•The five flavonoids can quench the fluorescence of pepsin.•Flavonoid-pepsin systems are driven by enthalpy and entropy.•Hydrophobic, hydrogen bonding and electrostatic are the main forces.•Baicalin binds pepsin in a more firmly way than the other four flavonoids.•The five flavonoids exert some influence on the secondary structure of pepsin. Baicalin, myricetin, rutin, hesperidin and isoliquiritin are five classic flavonoids. Being both dietary and biologically active compounds, the accurate and full basic data for clarifying the binding mechanisms of the five flavonoids to pepsin remain unclear. In this study, the binding of five classic flavonoids to pepsin was investigated by steady state and time-resolved fluorescence, circular dichroism (CD) spectroscopy combined with molecular docking methods. Fluorescence data reveal that the fluorescence quenching mechanisms of pepsin by the five flavonoids are all static quenching procedure. Baicalin has the strongest binding affinity and the binding affinity ranks in the order baicalin>hesperidin>isoliquiritin>rutin>myricetin. The thermodynamic analysis and molecular docking study conclude that the five flavonoids bind with pepsin mainly through hydrophobic interactions, as well as hydrogen bonding and electrostatic forces. Synchronous fluorescence spectroscopy and CD reveal that the microenvironment and conformation of pepsin are demonstrably changed in the presence of the flavonoids. The results of molecular docking show that hesperidin and isoliquiritin bind with the catalytic amino acid residues of pepsin. All these experimental results and theoretical data in this study are important in the field of pharmacology and biochemistry and will be helpful in understanding the digestion caused by flavonoids. [Display omitted]