Functional Regulation of Sugar Assimilation by N-Glycan-specific Interaction of Pancreatic α-Amylase with Glycoproteins of Duodenal Brush Border Membrane

Porcine pancreatic α-amylase (PPA) binds to N -linked glycans of glycoproteins (Matsushita, H., Takenaka, M., and Ogawa, H. (2002) J. Biol Chem. , 277, 4680–4686). Immunostaining revealed that PPA is located at the brush-border membrane (BBM) of enterocytes in the duodenum and that the binding is inhibited by mannan but not galactan, indicating that PPA binds carbohydrate-specifically to BBM. The ligands for PPA in BBM were identified as glycoprotein N -glycans that are significantly involved in the assimilation of glucose, including sucrase-isomaltase (SI) and Na + /Glc cotransporter 1 (SGLT1). Binding of SI and SGLT1 in BBM to PPA was dose-dependent and inhibited by mannan. Using BBM vesicles, we found functional changes in PPA and its ligands in BBM due to the N -glycan-specific interaction. The starch-degrading activity of PPA and maltose-degrading activity of SI were enhanced to 240 and 175%, respectively, while Glc uptake by SGLT1 was markedly inhibited by PPA at high but physiologically possible concentrations, and the binding was attenuated by the addition of mannose-specific lectins, especially from Galanthus nivalis . Additionally, recombinant human pancreatic α-amylases expressed in yeast and purified by single-step affinity chromatography exhibited the same carbohydrate binding specificity as PPA in binding assays with sugar-biotinyl polymer probes. The results indicate that mammalian pancreatic α-amylases share a common carbohydrate binding activity and specifically bind to the intestinal BBM. Interaction with N -glycans in the BBM activated PPA and SI to produce much Glc on the one hand and to inhibit Glc absorption by enterocytes via SGLT1 in order to prevent a rapid increase in blood sugar on the other. Background: PPA binds to specific glycoprotein N -glycans. Results: Interaction between PPA and glycoligands in duodenum BBM activates glucose production while inhibiting glucose absorption by enterocytes. Conclusion: N -Glycans in BBM function as a target for α-amylase in order to control glucose assimilation via their interaction. Significance: We have discovered the modulatory role of BBM glycoprotein N -glycans, which contribute to blood glucose homeostasis.