Structural insight into the glucose-6-phosphate transport by G6PT1 and inhibition mechanism of CGA.

Human glucose-6-phosphate transporter 1 (G6PT1) is responsible for transporting glucose-6-phosphate (G6P) into the endoplasmic reticulum (ER), a crucial rate-limiting step in both glycogenolysis and gluconeogenesis. Complete and chronic dysfunction of G6PT1 can lead to the severe metabolic disorder GSD1b, whereas moderate and reversible inhibition contributes to diabetes treatment. We determined the structures of human G6PT1 in its apo state and in complex with the substrate G6P, cosubstrate phosphate, and the inhibitor chlorogenic acid (CGA). Captured in both lumen- and cytosol-facing conformations, these structures reveal the specific mechanism of phosphate-coupled G6P transport. In addition, the CGA-bound G6PT1 complex shows that CGA stabilizes the transporter in the cytosol-facing conformation, inhibiting it by competing with substrate binding and preventing conformational transitions, providing previously unreported insights into G6PT1 inhibition. Our findings provide a structural foundation for understanding the mechanisms of substrate recognition, transport, drug inhibition, and the pharmacology of G6PT1, paving the way to the rational design of potential therapeutic agents.