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

¹ Columbia University
² Columbia University
³ Concepcion University
⁴ University of Concepcion
⁵ Columbia Univ. Col. of P&S

^* To whom correspondence should be addressed. E-mail: jf20{at}columbia.edu.

Submitted on June 18, 2004
Revised on July 26, 2004
Accepted on 9 August 2004

	Abstract

The glucose transporters (GLUT/SLC2A) are members of the major facilitator superfamily (MFS). Here, we generated a 3D model for Glut1 using a two-step strategy: (1) GlpT structure as initial homology template; (2) evolutionary homology using glucose-6-phosphate translocase (G6PU) as template. The resulting structure (PDB id: 1SUK) exhibits a water-filled passageway communicating the extracellular and intracellular domains, with a funnel-like exofacial vestibule (infundibulum), followed by a 15 Å long by 8 Å 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 Å away from the channel. Thus, 1SUK accounts for practically all biochemical and mutagenesis evidence, and provides clues for the transport process.

Key Words: cavities, channel, cytochalasin B, docking, forskolin, phloretin

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