Exploring the competitive inhibition mechanism of α-glucosidase by metformin.

Metformin (MET) is a commonly prescribed first-line drug for type 2 diabetes mellitus (T2DM) approved by the FDA. α-glucosidase is considered one of the effective therapeutic targets for T2DM. However, the potential interaction relationships between MET and α-glucosidase remain unclear. Therefore, this work comprehensively examined MET's impact on α-glucosidase, including binding mechanism, conformational changes, and structure-function relationships. Enzyme activity assays confirmed that MET exhibits competitive inhibition of α-glucosidase. Fluorescence spectroscopy and electrochemical experiments indicated that MET and α-glucosidase spontaneously form a static complex via hydrophobic interactions. This complex hindered the diffusion of [Fe(CN)6]3-/4- and lessened its diffusion coefficient. The secondary structure of the complex is less stable than that of α-glucosidase alone, as suggested by CD, AFM, and Rg, and this instability may lead to enzyme activity inhibition. Computer simulation revealed that MET establishes stable hydrogen bonding with α-glucosidase catalytic triad residues (Asp214, Glu276, and Asp349). Among these, Asp214 exhibits the highest hydrogen bond probability and lifetime. This interaction with the catalytic nucleophile likely underlies the competitive inhibition of α-glucosidase by MET. MD snapshots within 100 ns showed that MET forms a stable complex with α-glucosidase at the molecular level. Overall, these findings reveal an additional molecular mechanism by which MET inhibits α-glucosidase, providing evidence supporting its glucose-lowering efficacy in the treatment of T2DM.