Inhibitory mechanism of two allosteric inhibitors, oleanolic acid and ursolic acid on α-glucosidase

• Published in: International journal of biological macromolecules 2018-02, Vol.107 (Pt B), p.1844-1855
• Main Authors: Ding, Huafang, Hu, Xing, Xu, Ximing, Zhang, Guowen, Gong, Deming
• Format: Article
• Language: English
• Subjects: Acarbose - chemistry; Acarbose - pharmacology; Allosteric Regulation - drug effects; Allosteric Site; Circular Dichroism; Enzyme Activation - drug effects; Glycoside Hydrolase Inhibitors - chemistry; Glycoside Hydrolase Inhibitors - pharmacology; Inhibition mechanism; Kinetics; Molecular Dynamics Simulation; Oleanolic Acid - chemistry; Oleanolic Acid - pharmacology; Pentacyclic triterpenes; Saccharomyces cerevisiae - enzymology; Spectrometry, Fluorescence; Thermodynamics; Time Factors; Triterpenes - chemistry; Triterpenes - pharmacology; Ursolic Acid; α-Glucosidase
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2017.10.040

•Oleanolic acid and ursolic acid reversibly inhibited α-glucosidase in a non-competitive manner.•Oleanolic acid and ursolic acid bound to different allosteric sites of α-glucosidase to induce allosteric regulation.•Oleanolic acid and ursolic acid induced the conformational changes of α-glucosidase.•Oleanolic acid and ursolic acid showed a synergy on the inhibition of α-glucosidase. Glycemic control which can be efficaciously regulated by inhibiting α-glucosidase activity is an effective therapy for diabetes mellitus. This work is to investigate the kinetics and inhibition mechanism of oleanolic acid and ursolic acid on α-glucosidase. Oleanolic acid and ursolic acid exhibited potent inhibitory activities with IC50 values of (6.35±0.02)×10−6 and (1.69±0.03)×10−5molL−1 respectively in a reversible and non-competitive manner. Both of them binding to α-glucosidase induced the conformational change and intrinsic fluorescence quenching of α-glucosidase. The binding constants of oleanolic acid and ursolic acid with α-glucosidase at 298K were (2.04±0.02)×103 and (1.87±0.02)×103Lmol−1, respectively. Docking results showed that oleanolic acid and ursolic acid bound in different allosteric sites of cavity 2 and cavity 4 on α-glucosidase, respectively, which triggered allosteric regulation to perturb conformational dynamics of α-glucosidase, eventually leading to a decrease of catalytic activity of the enzyme. The substrate was not catalyzed by α-glucosidase to generate further products due to formation of a nonreactive ternary complex of oleanolic acid– or ursolic acid–α-glucosidase–substrate. The combination of oleanolic acid and ursolic acid displayed a significant synergistic inhibition on α-glucosidase.