Exploring the competitive inhibition of α-glucosidase by citrus pectin enzymatic hydrolysate and its mechanism: An integrated experimental and simulation approach.

The endo-polygalacturonase D (PgaD) from Aspergillus niger JL15 was recombinantly expressed in Escherichia coli BL21, exhibiting an optimal activity at 55 °C and pH 4.0. Hydrolysis products of citrus pectin by recombinant PgaD included galacturonic acid (GalA), digalacturonic acid (GalA2), trigalacturonic acid (GalA3), and tetragalacturonic acid (GalA4). The hydrolysates exhibited significant antioxidant capacity and dose-dependent competitive inhibition of α-glucosidase. GalA2 and GalA3 acted as competitive inhibitors of α-glucosidase, with inhibition constant of 0.0589 mmol.L and 0.6732 mmol.L, respectively. Molecular dynamics (MD) simulations revealed that both GalA2 and GalA3 penetrated the catalytic pocket of α-glucosidase and formed stable hydrogen bonds with key catalytic residues D352 and D215. The binding free energies of GalA2-α-glucosidase and GalA3-α-glucosidase complexes were - 10.3 ± 0.6 kcal·mol and -10.8 ± 0.7 kcal·mol, respectively. These findings might offer new ideas for the development of α-glucosidase inhibitors sourced from citrus pectin, as well as enhance utilization of the renewable plant polysaccharide resources.