CHARACTERIZATION OF GLUT5 DOMAINS RESPONSIBLE FOR FRUCTOSE TRANSPORT

The domains responsible for the fructose specificity of GLUTS were inv estigated by creating chimeras of GLUTS with the selective glucose tra nsporter GLUTS, which were expressed in Xenopus oocytes. 3-O-Methylglu cose uptake of chimeric GLUT3-5 (M11; GLUTS to the 11th transmembrane domain, GLUTS to the carboxyl end) was similar to that of GLUTS, while fructose was not transported. Fructose uptake of chimeric GLUT5-S (M3 -5) to -5 (GLUTS from the 3rd to 5th transmembrane domains, the rest G LUTS) was similar to that of GLUTS; no glucose was transported. Four c himeras transported neither fructose nor glucose: GLUT3-5 (MS; GLUTS t o the 5th transmembrane domain, GLUTS to the carboxyl end), GLUT5-3 (M 2; GLUTS to the 2nd transmembrane domain, the rest GLUTS), GLUTS-3 (M3 -11) to -5 (GLUTS between the 3rd and 11th transmembrane domains, the rest GLUTS) and GLUT5-3 (M3-5) to -5-3 (M11; GLUTS from the 3rd to 5th transmembrane domains and after the 11th transmembrane domain, the re st GLUTS). They, nevertheless, induced full-size proteins that were tr ansported to the cell surface, as demonstrated by exofacial labeling w ith biotin. To conclude, the GLUTS domain from the amino-terminus to t he third transmembrane domain and that between the 5th and 11th transm embrane stretches seem to be necessary for fructose uptake.