Structural insights into the mechanism of the human SGLT2-MAP17 glucose transporter

Selective sodium-glucose cotransporter 2 (SGLT2) plays an important role in glucose reabsorption. SGLT2 inhibitors suppress glucose reabsorption from the kidneys, thus reducing blood glucose levels in type 2 diabetes patients. We and other groups have developed several SGLT2 inhibitors starting from a natural product, phlorizin, but their action mechanisms remain unknown. Here, we elucidated the physiological hSGLT2-MAP17 complex structures bound to five SGLT2 inhibitors using single-particle cryo-electron microscopy. Canagliflozin, dapagliflozin, TA-1887, and sotagliflozin were bound in the outward-facing structure, whereas phlorizin was bound in the inward-open structure. The phlorizin-hSGLT2 interaction biochemically exhibited biphasic binding. Phlorizin weakly binds, via the phloretin motif, from its intracellular side near the Na+-binding site, while strongly interacts from its extracellular side. Unexpectedly, bound Na+ stabilizes the outward-open conformation, while its release allows the transporter to adopt inward-open state. Our results first visualized the Na+-binding and inward-open conformation of hSGLT2-MAP17, clarifying the unprecedented Na+-dependent sugar transport mechanism with MAP17 acting as a scaffold, and may pave the way for development of next-generation SGLT inhibitors.