Docking studies show that D-glucose and quercetin slide through the transporter GLUT1.
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 A of 10 glucose transporter deficiency syndrome missense mutations. Another three sites are within 8 A 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 (K(i) = 2.4 mum) 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, Glu(254) and Lys(256) hydrogen-bond quercetin (K(i) approximately 10 microm) 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. Beta-D-hexoses dock twice as frequently as their alpha-anomers to the 23 aromatic residues in the transport pathway, suggesting that endocyclic hexose hydrogens, as with maltosaccharides in maltoporins, form pi-bonds with aromatic rings and slide between sites instead of being translocated via a single alternating site.
Cunningham
Philip
P
Bioinformatics, Franklin-Wilkins Building, King's College London, London SE1 9NH, United Kingdom.
Afzal-Ahmed
Iram
I
Naftalin
Richard J
RJ
D001665:Binding Sites; D001692:Biological Transport / Q000502:physiology; D004912:Erythrocytes / Q000378:metabolism; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D051272:Glucose Transporter Type 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010693:Phloretin / Q000378:metabolism; D011487:Protein Conformation; D011794:Quercetin / Q000737:chemistry / Q000378:metabolism*
D051272:Glucose Transporter Type 1; C495677:SLC2A1 protein, human; D011794:Quercetin; D005947:Glucose; D010693:Phloretin