Study of the interaction mechanisms of ellagitannins from Phyllanthus emblica L. with acetylcholinesterase using multi-spectroscopy, molecular docking, and molecular dynamic

Abstract

Ellagitannins, a class of hydrolysable tannins widely present in Phyllanthus emblica L., exhibit inhibitory effects on acetylcholinesterase (AChE) activity; however, their inhibition mechanisms remain poorly characterized to date. In this study, the inhibition mechanism between four ellagitannins and AChE was systematically analyzed by integrating enzyme inhibition kinetics, multi-spectral analysis, molecular docking and molecular dynamics simulation. Enzyme inhibition kinetics indicated that all four ellagitannins were reversible inhibitors of AChE, with corilagin being a mixed inhibitor and ellagic acid, geraniin and chebulagic acid being uncompetitive inhibitors. Fluorescence spectroscopy confirmed that the four ellagitannins formed complexes with AChE and quenched the intrinsic fluorescence of AChE through static quenching, with only one binding site. The binding was mainly driven by hydrogen bonds and van der Waals forces, and the binding process was an enthalpy-driven spontaneous exothermic process. It can also quench the synchronous fluorescence of tyrosine (Tyr) and tryptophan (Trp), and change the microenvironment around the tryptophan residues. Fluorescence resonance energy transfer further verified that the fluorescence quenching was the result of non-radiative energy resonance and static quenching. UV–vis, FT-IR and CD spectroscopy results showed that the formation of enzyme-inhibitor complexes altered the secondary structure of AChE. Molecular docking and molecular dynamics simulation further verified that the four ellagitannins embedded in the hydrophobic pocket of AChE to form stable complexes, and formed hydrogen bonds with surrounding amino acid residues, making the enzyme structure more stable and hindering the entry of substrates, ultimately inhibiting AChE activity. Overall, our study provides novel insights into ellagitannins as natural AChE inhibitors and their potential as therapeutic candidates for Alzheimer’s disease.