Predicting the Three-Dimensional Structure of the Human Facilitative Glucose Transporter Glut1 by a Novel Evolutionary Homology Strategy: Insights on the Molecular Mechanism of Substrate Migration, and Binding Sites for Glucose and Inhibitory Molecules

Abstract

The glucose transporters (GLUT/SLC2A) are members of the major facilitator superfamily. Here, we generated a three-dimensional model for Glut1 using a two-step strategy: 1), GlpT structure as an initial homology template and 2), evolutionary homology using glucose-6-phosphate translocase as a template. The resulting structure (PDB No. 1SUK) exhibits a water-filled passageway communicating the extracellular and intracellular domains, with a funnel-like exofacial vestibule (infundibulum), followed by a 15 A-long x 8 A-wide channel, and a horn-shaped endofacial vestibule. Most residues which, by mutagenesis, are crucial for transport delimit the channel, and putative sugar recognition motifs (QLS, QLG) border both ends of the channel. On the outside of the structure there are two positively charged cavities (one exofacial, one endofacial) delimited by ATP-binding Walker motifs, and an exofacial large side cavity of yet unknown function. Docking sites were found for the glucose substrate and its inhibitors: glucose, forskolin, and phloretin at the exofacial infundibulum; forskolin, and phloretin at an endofacial site next to the channel opening; and cytochalasin B at a positively charged endofacial pocket 3 A away from the channel. Thus, 1SUK accounts for practically all biochemical and mutagenesis evidence, and provides clues for the transport process.

Essential Molecular Determinants for Thyroid Hormone Transport and First Structural Implications for Monocarboxylate Transporter 8

“…With small deviations, the helix dimensions observed in the GlpT crystal structure are applicable for human MCT8. The reliability of this structural template is supported by examples of modeling for other members of the MFS-like GLUT1 (22) or MCT1 (23,24 Comparison with loop conformations extracted from the PDB by the SuperLooper bioinformatics software were also performed to find superimposing loop structures from the PDB as criteria for reliability. The quality and stability of the model were validated by checking the geometry using PROCHECK (25).…”

Docking Studies Show That D-Glucose and Quercetin Slide through the Transporter GLUT1

“…The glucose uniporter GLUT1 (SLC2A1), a member of the major facilitator superfamily of solute transporters, has to date not been crystallized, but its three-dimensional structure has been modeled by templating it to that of Lac Y permease and glycerol 3-phosphate antiporter (GlpT) from Escherichia coli (1)(2)(3). The 12 transmembrane ␣-helical domains of the monomeric GLUT protein are arranged around a central water-filled pore lined predominantly with uncharged hydrophilic and hydrophobic amino acids.…”

“…Molecular dynamic simulations show that glucose binds close to this position within the pore, as expected of lactose binding to Lac Y permease (2). Glucose docks additionally in a cavity at the external entrance of the pore (3).…”

“…Attention has been drawn to the structural similarity between GLUT1 and maltoporins (3). Large numbers of aromatic amino acids line the "greasy pore" of maltoporin and the central pore of the GLUT1.…”

“…GLUT1 deficiency syndrome (GLUT1-DS) 3 is caused by an inadequate energy supply to brain with failure of growth and development of the central nervous system resulting from diminished glucose transport across the blood brain barrier via defective endothelial GLUT1. The children affected tend to develop microcephaly, epileptic seizures, and ataxia.…”