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Lan Wu, Jeffery D. Fritz, Alvin C. Powers, Different Functional Domains of GLUT2 Glucose Transporter Are Required for Glucose Affinity and Substrate Specificity
*, Endocrinology, Volume 139, Issue 10, 1 October 1998, Pages 4205–4212, https://doi.org/10.1210/endo.139.10.6245This work was supported by grants from the Department of Veterans Affairs Research Service (Career Development Award and Merit Review Award), a fellowship award from the Juvenile Diabetes Foundation International (to L.W.), and the Vanderbilt Diabetes Research and Training Center (NIH Grant DK-20593).
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Abstract
GLUT2 is the major glucose transporter in pancreatic β-cells and hepatocytes. It plays an important role in insulin secretion fromβ -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.