Investigation on interaction between Ligupurpuroside A and pepsin by spectroscopic and docking methods

•The interaction of Ligupurpuroside A with pepsin was investigated.•Non-covalent reactions were the main forces.•Energy transfer occurred between Ligupurpuroside A and pepsin.•Synchronous fluorescence was performed to analyze the conformational changes.

Ligupurpuroside A is one of the major glycoside in Ku-Din-Cha, a type of Chinese functional tea. In order to better understand its digestion and metabolism in humans, the interaction between Ligupurpuroside A and pepsin has been investigated by fluorescence spectra, UV–vis absorption spectra and synchronous fluorescence spectra along with molecular docking method. The fluorescence experiments indicate that Ligupurpuroside A can effectively quench the intrinsic fluorescence of pepsin through a combined quenching way at the low concentration of Ligupurpuroside A, and a static quenching procedure at the high concentration. The binding constant, binding sites of Ligupurpuroside A with pepsin have been calculated. The thermodynamic analysis suggests that non-covalent reactions, including electrostatic force, hydrophobic interaction and hydrogen bond are the main forces stabilizing the complex. According to the Förster’s non-radiation energy transfer theory, the binding distance between pepsin and Ligupurpuroside A was calculated to be 3.15 nm, which implies that energy transfer occurs between pepsin and Ligupurpuroside A. Conformation change of pepsin was observed from UV–vis absorption spectra and synchronous fluorescence spectra under experimental conditions. In addition, all these experimental results have been validated by the protein-ligand docking studies which show that Ligupurpuroside A is located in the cleft between the domains of pepsin.

Graphical abstractThe binding complex was formed by non-covalent reactions between Ligupurpuroside A and pepsin, which resulted in the obvious decrease in the fluorescence intensity of pepsin. The binding constants of Ligupurpuroside A with pepsin were determined at three different temperatures based on fluorescence quenching results. Conformational change of pepsin upon interaction with Ligupurpuroside A was studied. The docking studies results show that Ligupurpuroside A is located in the cleft between the domains of pepsin.Figure optionsDownload full-size imageDownload as PowerPoint slide