GLUCOSE-TRANSPORT ACTIVITY AND LIGAND-BINDING (CYTOCHALASIN-B, IAPS-FORSKOLIN) OF CHIMERIC CONSTRUCTS OF GLUT2 AND GLUT4 EXPRESSED IN COS-7-CELLS

Chimeric constructs of glucose transporters GLUT2 and GLUT4 were trans iently expressed in COS-7 cells in order to determine regions of the p roteins responsible for their differences in activity and ligand bindi ng. Exchange of the C-terminal tail (aa 479-509) of GLUT4 failed to af fect glucose transport activity assayed an 1 mM glucose or ligand bind ing (cytochalasin B, IAPS-forskolin). In contrast, exchange of the C-t erminal half of GLUT4 (aa 222-509) for that of GLUT2 markedly reduced ligand binding (Kd of cytochalasin B binding 1.88+/-0.2 mu M vs. 0.21/-0.06 in the wild-type GLUT4), and moderately (25%) reduced glucose t ransport activity. These data support the conclusion that the domains determining differences in ligand binding between GLUT4 and GLUT2 are located in the C-terminal half of the glucose transporters.