Crystal structure of a bacterial homologue of glucose transporters GLUT1–4

Glucose transporters are essential for metabolism of glucose in cells of diverse organisms from microbes to humans, exemplified by the disease-related human proteins GLUT1, 2, 3 and 4. Despite rigorous efforts, the structural information for GLUT1–4 or their homologues remains largely unknown. Here we report three related crystal structures of XylE, an Escherichia coli homologue of GLUT1–4, in complex with d-xylose, d-glucose and 6-bromo-6-deoxy-d-glucose, at resolutions of 2.8, 2.9 and 2.6 Å, respectively. The structure consists of a typical major facilitator superfamily fold of 12 transmembrane segments and a unique intracellular four-helix domain. XylE was captured in an outward-facing, partly occluded conformation. Most of the important amino acids responsible for recognition of d-xylose or d-glucose are invariant in GLUT1–4, suggesting functional and mechanistic conservations. Structure-based modelling of GLUT1–4 allows mapping and interpretation of disease-related mutations. The structural and biochemical information reported here constitutes an important framework for mechanistic understanding of glucose transporters and sugar porters in general.