Inhibitory mechanism of Tangzhiqing on sucrase: changed inhibitory kinetics and secondary molecular conformation of sucrase and chemical components from Tangzhiqing.

BACKGROUND

Tangzhiqing (TZQ), a herbal formula, has postprandial hypoglycemic effects on sucrose in humans. Sucrase, an α-glucosidase, breaks down sucrose into glucose and fructose. This study investigated the inhibitory activity of TZQ against sucrase and the associated conformational changes.

METHODS

Inhibitory activity was assessed using sucrose as substrate. After confirming the suitable reaction concentrations and time, an assay of the inhibitory activity of TZQ against sucrase was performed with a series of TZQ concentrations. The inhibition kinetics were analyzed in the presence and absence of TZQ or acarbose (positive control). Secondary structure changes of sucrase were determined by circular dichroism spectroscopy. Components of TZQ were identified by UPLC-Q-TOF/MS, and molecular docking explored binding interactions.

RESULTS

TZQ showed notable inhibitory activity against sucrase in a reversible and uncompetitive manner. The half-maximal inhibitory concentrations of TZQ and acarbose were 1.49 ± 0.07 and 3.94 ± 0.07 µg/mL (P < 0.01), respectively. Circular dichroism revealed that TZQ binding induced secondary structural rearrangement of sucrase, increasing α-helix and decreasing β-sheet content, thereby inhibiting enzyme activity. A total of 64 chemical ingredients were identified from TZQ. Among these, the potential active ingredients-including paeoniflorin, vitexin, chlorogenic acid, and salvianolic acid A-exhibited binding energies below - 5 kcal/mol. These compounds strongly affected the structure of sucrase via π accumulation or salt bridge formation, leading to enzyme inhibition and reduced glucose.

CONCLUSION

These findings provide new insights into the inhibitory mechanism of TZQ on sucrase, supporting its potential as a novel α-glucosidase inhibitor for the management of type 2 diabetes mellitus.