Analysis of the structural requirements of sugar binding to the liver, brain and insulin-responsive glucose transporters expressed in oocytes

Abstract

We have expressed the liver (GLUT 2), brain (GLUT 3) and insulin-responsive (GLUT 4) glucose transporters in oocytes from Xenopus laevis by microinjection of in vitro-transcribed mRNA. Using a range of halogeno- and deoxy-glucose analogues, and other hexoses, we have studied the structural basis of sugar binding to these different isoforms. We show that a hydrogen bond to the C-3 position is involved in sugar binding for all three isoforms, but that the direction of this hydrogen bond is different in GLUT 2 from either GLUT 1, 3 or 4. Hydrogen-bonding at the C-4 position is also involved in sugar recognition by all three isoforms, but we propose that in GLUT 3 this hydrogen bond plays a less significant role than in GLUT 2 and 4. In all transporters we propose that the C-4 position is directed out of the sugar-binding pocket. The role of the C-6 position is also discussed. In addition, we have analysed the ability of fructopyranose and fructofuranose analogues to inhibit the transport mediated by GLUT2. We show that fructofuranose analogues, but not fructopyranose analogues, are efficient inhibitors of transport mediated by GLUT 2, and therefore suggest that GLUT 2 accommodates D-glucose as a pyranose ring, but D-fructose as a furanose ring. Models for the binding sites of GLUT 2, 3 and 4 are presented.

Substrate Recognition at the Cytoplasmic and Extracellular Binding Site of the Lactose Transport Protein of Streptococcus thermophilus

“…The hydrophobic surface incorporating these hydrogen atoms would be a candidate for interaction with aromatic residues in the binding site. In contrast, bound [1][2][3][4][5][6][7][8][9][10][11][12][13] C]D-galactose observed with cross-polarization magic-angle spinning NMR showed no significant difference in chemical shift compared with galactose in free solution, which is indicative of a comparable chemical environment (24). This would be consistent with C-1 being remote from the hydrophobic surface, as viewed in Fig.…”

“…As no such information is available for sugar transport systems, an alternative approach was sought to dissect the structural requirements for substrate binding by LacS. Substrate specificity studies have proven to give valuable insight into the nature of the interactions between the sugar and the protein in case of the human sugar transporters Glut1-4 (11,12) and their Escherichia coli homologues the galactose (GalP) and L-arabinose (AraE) proton symporters (13,14), the lactose permease LacY from E. coli (15,16), the human intestinal brush border glucose/Na ϩ cotransporter SGLT1 (17), the Trypanosoma brucei bloodstream form transporter THT1 (18), and the human active renal hexose transporter (19). Most of these studies, however, do not discriminate between sugar binding to the cytoplasmic and extracellular binding site.…”

Carrier‐mediated transport systems for glucose in mucosal cells of the human oral cavity

“…22 On the other hand, D-allose is an effective inhibitor of glucose transport by GLUT2, but not by GLUT1, 3, or 4. 22 Thus, multiple facilitative transporters are suggested to be present in the oral mucosal cells. In addition, it was clarified by the buccal absorption test of 2-deoxy-D-glucose that the facilitative transport system is expressed on the apical surface of the stratified squamous epithelium.…”

“…DMannose is transported by GLUTs1-4. 21,22 Maltose is an inhibitor of glucose transport by GLUT3, but not by GLUT2 or 4. 22 On the other hand, D-allose is an effective inhibitor of glucose transport by GLUT2, but not by GLUT1, 3, or 4.…”

“…21,22 Maltose is an inhibitor of glucose transport by GLUT3, but not by GLUT2 or 4. 22 On the other hand, D-allose is an effective inhibitor of glucose transport by GLUT2, but not by GLUT1, 3, or 4. 22 Thus, multiple facilitative transporters are suggested to be present in the oral mucosal cells.…”