Exploring inhibition mechanism and nature of lipase by Ligupurpuroside A extracted from Ku-Ding tea

Enzyme-activity essay demonstrated that Ligupurpuroside A acts as a natural inhibitor of lipase in a competitive manner. The inhibition mechanism and nature of lipase by Ligupurpuroside A were investigated by fluorescence spectra, UV–Vis absorption spectra, circular dichroism (CD) spectra and molecular docking methods. Fluorescence experiments indicated that Ligupurpuroside A can quench the intrinsic fluorescence of lipase through a static quenching procedure. Thermodynamic analysis suggested that hydrophobic interaction is the main force between lipase and Ligupurpuroside A. Fluorescence resonance energy transfer experiment showed that an energy transfer from lipase to Ligupurpuroside A occurs with great possibility, confirming the presence of static quenching mechanism of lipase fluorescence by Ligupurpuroside A. Interestingly, conformation of lipase remained almost the same after bound to Ligupurpuroside A based on CD spectral experiments. All these experimental results were validated by the protein-ligand docking studies which further showed that Ligupurpuroside A could bind to the amino acid residues of the hydrophobic cavity on catalytic sites of lipase. This study should be helpful for the design of diet drug and the full use of Ligupurpuroside A in food industry.