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

• Published in: The Journal of biological chemistry Vol. 281; no. 9; pp. 5797 - 5803
• Main Authors: Cunningham, Philip, Afzal-Ahmed, Iram, Naftalin, Richard J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 03.03.2006; American Society for Biochemistry and Molecular Biology
• Subjects: Binding Sites; Biological Transport - physiology; Erythrocytes - metabolism; Glucose - chemistry; Glucose - metabolism; Glucose Transporter Type 1 - chemistry; Glucose Transporter Type 1 - genetics; Glucose Transporter Type 1 - metabolism; Humans; Hydrogen Bonding; Models, Molecular; Molecular Sequence Data; Mutation; Phloretin - metabolism; Protein Conformation; Quercetin - chemistry; Quercetin - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M509422200

On a three-dimensional templated model of GLUT1 (Protein Data Bank code 1SUK), a molecular recognition program, AUTODOCK 3, reveals nine hexose-binding clusters spanning the entire “hydrophilic” channel. Five of these cluster sites are within 3-5 Å of 10 glucose transporter deficiency syndrome missense mutations. Another three sites are within 8 Å of two other missense mutations. d-Glucose binds to five sites in the external channel opening, with increasing affinity toward the pore center and then passes via a narrow channel into an internal vestibule containing four lower affinity sites. An external site, not adjacent to any mutation, also binding phloretin but recognizing neither d-fructose nor l-glucose, may be the main threading site for glucose uptake. Glucose exit from human erythrocytes is inhibited by quercetin (Ki = 2.4 μm) but not anionic quercetin-semiquinone. Quercetin influx is retarded by extracellular d-glucose (50 mm) but not by phloretin and accelerated by intracellular d-glucose. Quercetin docking sites are absent from the external opening but fill the entire pore center. In the inner vestibule, Glu254 and Lys256 hydrogen-bond quercetin (Ki ≈ 10 μm) but not quercetin-semiquinone. Consistent with the kinetics, this site also binds d-glucose, so quercetin displacement by glucose could accelerate quercetin influx, whereas quercetin binding here will competitively inhibit glucose efflux. β-d-Hexoses dock twice as frequently as their α-anomers to the 23 aromatic residues in the transport pathway, suggesting that endocyclic hexose hydrogens, as with maltosaccharides in maltoporins, form π-bonds with aromatic rings and slide between sites instead of being translocated via a single alternating site.