Different functional domains of GLUT2 glucose transporter are required for glucose affinity and substrate specificity.
GLUT2 is the major glucose transporter in pancreatic beta-cells and hepatocytes. It plays an important role in insulin secretion from beta-cells and glucose metabolism in hepatocytes. To better understand the molecular determinants for GLUT2's distinctive glucose affinity and its ability to transport fructose, we constructed a series of chimeric GLUT2/GLUT3 proteins and analyzed them in both Xenopus oocytes and mammalian cells. The results showed the following. 1) GLUT3/GLUT2 chimera containing a region from transmembrane segment 9 to part of the COOH-terminus of GLUT2 had Km values for 3-O-methylglucose similar to those of wild-type GLUT2. Further narrowing of the GLUT2 component in the chimeric GLUTs lowered the Km values to those of wild-type GLUT3. 2) GLUT3/GLUT2 chimera containing a region from transmembrane segment 7 to part of the COOH-terminus of GLUT2 retained the ability to transport fructose. Further narrowing of this region in the chimeric GLUTs resulted in a complete loss of the fructose transport ability. 3) Chimeric GLUTs with the NH2-terminal portion of GLUT2 were unable to express glucose transporter proteins in either Xenopus oocytes or mammalian RIN 1046-38 cells. These results indicate that amino acid sequences in transmembrane segments 9-12 are primarily responsible for GLUT2's distinctive glucose affinity, whereas amino acid sequences in transmembrane segments 7-8 enable GLUT2 to transport fructose. In addition, certain region(s) of the amino-terminus of GLUT2 impose strict structural requirements on the carboxy-terminus of the glucose transporter protein. Interactions between these regions and the carboxy-terminus of GLUT2 are essential for GLUT2 expression.
Wu
L
L
Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232, USA.
Fritz
J D
JD
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D000818:Animals; D005260:Female; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D051273:Glucose Transporter Type 2; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014982:Xenopus laevis
D051273:Glucose Transporter Type 2; D009004:Monosaccharide Transport Proteins; D011993:Recombinant Fusion Proteins; D005632:Fructose; D005947:Glucose