Counter-Current Fractionation-Assisted Bioassay-Guided Separation of Active Compound from Blueberry and the Interaction between the Active Compound and α-Glucosidase

C NMR. The interaction mechanism between C3G and α-glucosidase was clearly characterized and described by spectroscopic methods, including fluorescence and circular dichroism (CD) in combination with molecular docking techniques. C3G could spontaneously bind with α-glucosidase to form complexes by hydrogen bonds. The secondary structure of α-glucosidase changed in varying degrees after complexation with C3G. The α-helical and β-turn contents of α-glucosidase decreased, whereas the β-sheet content and the irregular coil structures increased. Molecular docking speculated that C3G could form hydrogen bonds with α-glucosidase by binding to the active sit (Leu 313, Ser 157, Tyr 158, Phe 314, Arg 315, and two Asp 307). These findings may be useful for the development of functional foods to tackle type 2 diabetes.