C-terminal truncated glucose transporter is locked into an inward-facing form without transport activity

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Abstract
THE facilitated glucose transporters comprise a structurally related family of proteins predicted to have 12 membrane-spanning domains, with the amino terminus, a relatively large middle loop and the carboxy-terminus all oriented towards the cytoplasm1–10. An alternating conformation model has been proposed to explain the mechanism of facilitated glucose transport11–17. To understand the structure-function relationships, especially the role of the intracellular C-terminal domain, we have modified the rabbit equivalent of the erythroid-type transporter, GLUT1 (réf. 18), using complementary DNA to code for a deletion mutant that lacks most (37 out of 42 amino acids) of the intracellular C-terminal domain. This deletion mutant is expressed at the cell surface of Chinese hamster ovary (CHO) cells, but is functionally inactive, probably because it has lost its capacity to alternate in conformation and so is locked into an inward-facing form.