Exploring the structure-activity relationship and interaction mechanism of flavonoids and alpha-glucosidase based on experimental analysis and molecular docking studies
-Glucosidase (AG) has always been as an indispensable drug target for the treatment of type 2 diabetes. Herein, an integrated method consisted of enzyme kinetics, multi-spectroscopic assay and molecular simulations was performed to investigate the structure-activity relationship and interaction mechanism of flavonoids and AG. As a result, a small amount of flavonoids were found to present excellent inhibitory activity on AG, such as 3, 5, 6, 8, 10, 17, 19, 21, 22 and 34. Further analysis of structure-activity relationship illustrated that the hydroxylation at the positions C3, C6, C3’ and C4’ of flavonoid caused an increase in the inhibitory activity of AG, whereas the methoxylation at the corresponding positions would decrease the activity. Also, it was found that the glycosylation and hydrogenation of the C2 C3 double bond would distinctly reduce the inhibition potency. Therefore, various groups at different positions of flavonoids exhibited upward and downward tendency on the activity. According to the fluorescence quenching assay, all of the test flavonoids could effectively quench the intrinsic fluorescence of AG based on either static or mixed static-dynamic mechanism. Besides, the thermodynamic parameters of representative flavonoid 19 revealed the spontaneous characteristic of binding process with AG, and highlighted the critical role of hydrophobic interaction and hydrogen bonds. Moreover, the results obtained from the synchronous fluorescence, ANS-binding fluorescence, Fourier transform infrared and circular dichroism spectra illustrated that these active flavonoids could bind to the active site of AG, and induce the rearrangement and conformation change of its secondary structures, which resulted in the significant inhibitory activity. Additionally, molecular modelling visualized the preferred binding conformation of flavonoids on AG, and further confirmed the great importance of hydrophobic interaction and hydrogen bonds for the interaction. Such findings provided new insights into understanding the proposed interaction behavior between flavonoids and AG, and were helpful to develop novel AG inhibitors relying on flavonoid scaffold for the treatment of type 2 diabetes.