Evidence that functional erythrocyte-type glucose transporters are oligomers

In this study we tested the hypothesis that functional erythrocyte-type glucose transporters (GLUT1) exist as oligomeric complexes by expressing chimeric transporter proteins in Chinese hamster ovary cells harboring endogenous GLUT1 transporters. The chimeric transporters were GLUT1-4c, in which the 29 C-terminal residues of human GLUT1 were replaced by the 30 C-terminal residues of rat skeletal muscle glucose transporter (GLUT4), and GLUT1n-4, containing the N-terminal 199 residues of GLUT1 and the 294 C-terminal residues of GLUT4. Endogenous GLUT1 was quantitatively co-immunoprecipitated by using an anti-GLUT4 C-terminal peptide antibody from detergent extracts of Chinese hamster ovary cells expressing either of the chimeric proteins, as detected by immunoblotting the precipitates with an anti-GLUT1 C-terminal peptide antiserum. No co-immunoprecipitation of native GLUT1 with native GLUT4 from extracts of 3T3-L1 adipocytes, which contain both these transporters, was observed with the same antibody. These data are consistent with the hypothesis that GLUT1 transporters exist as homodimers or higher order oligomers and that a major determinant of oligomerization is located within the first 199 residues of GLUT1.