Mechanistic Insights into the Substrate Egress Pathways of Human Glucose Transporters GLUT1 and GLUT9

Glucose transporters (GLUTs) play critical roles in cellular energy homeostasis and substrate-specific transport. Dysfunctional mutations can cause GLUT1 deficiency syndrome and excessive expression of GLUT1 is linked to cancer progression; while abnormal regulation of urate transport by GLUT9 is associated with hyperuricemia and gout. In this study, machine-learning driven molecular dynamics simulations have been employed to investigate the mechanistic insights into the substrate egress pathways of GLUT1 and GLUT9, including the inhibition mechanism of GLUT9 by apigenin. Our findings reveal that intracellular helices play a crucial role in facilitating the transition from inward-closed to inward-open conformations in both transporters. Additionally, aromatic residues, F291 and W388 in GLUT1, and W336 and F435 in GLUT9, are identified as key mediators of conformational changes. Analysis of substrate exit pathways provides mechanistic insights into transport profiles and aligns with clinically observed mutations. Furthermore, the inhibitory effect of apigenin on GLUT9 is shown to arise from steric hindrance due to increased substrate size, rather than stable interactions. These findings enhance our understanding of GLUT transporter dynamics and highlight the potential of targeting substrate pathways for therapeutic intervention.