Molecular docking and muiltple spectroscopy investigation on the binding characteristics of aloe-emodin to pepsin

In this study, the binding characteristics of aloe-emodin (AE) and pepsin were investigated via multiple spectroscopic and molecular docking methods. The Stern-Volmer quenching constant (Ksv) suggested that AE quenched the fluorescence intensity of pepsin via static quenching. The value of the stoichiometric binding number (n) suggested only a single binding site on pepsin for AE. The value of Gibbs' free energy change (Delta G) < 0 indicated a spontaneous binding mechanism. The negative values of enthalpy change (Delta H) and entropy change (Delta S) indicated that hydrogen bonds and van der Waals forces were the main forces mediating the binding process. The conformational changes in the structure of pepsin were confirmed by synchronous, three-dimensional fluorescence and Fourier-transform infrared (FT-IR) spectroscopy. The alpha-helix and beta-sheet content of pepsin decreased, whereas the random coil and beta-turn content increased. Molecular docking results further validated the findings and displayed the specific mode of interaction. The catalytic activity of pepsin and the antioxidant effect of AE were decreased upon binding of the two molecules. This study provides a theoretical basis for protecting the antioxidant activity of AE and suggests strategies to improve the safety of foods and regulate the multiple biologically relevant processes. (C) 2019 Published by Elsevier B.V.