2.A.1.1.3
Xylose (xylopyranose):H⁺ symporter of 491 aas and 12 TMSs (Wambo et al. 2017).  Also transports and binds D-glucose and 6-bromo-6-deoxy-D-glucose.  The 3-d structure is known in three conformers, outward occluded, inward occluded and inward open (Sun et al. 2012: Quistgaard et al. 2013).  Most of the sugar-binding residues are conserved with the human Glut-1, 2, 3 and 4 homologues.  The coalescence of intramolecular tunnels and cavities has been postulated to account for facilitated diffusion of sugars (Cunningham and Naftalin 2014). Protonation of a conserved aspartate triggers a conformational transition from the outward-facing to the inward-facing state. This transition only occurs in the presence of substrate xylose, while the inhibitor glucose locks the transporter in the outward-facing stateQuistgaard et al. 2013).  Most of the sugar-binding residues are conserved with the human Glut-1, 2, 3 and 4 homologues.  The coalescence of intramolecular tunnels and cavities has been postulated to account for facilitated diffusion of sugars (Cunningham and Naftalin 2014). Protonation of a conserved aspartate triggers a conformational transition from the outward-facing to the inward-facing state. This transition only occurs in the presence of substrate xylose, while the inhibitor glucose locks the transporter in the outward-facing state (Jia et al. 2020).