Identification and characterization of a novel glucose transporter binding protein

One mechanism for regulating the function of facultative glucose transporters is thought to occur via their direct interaction with proteins that modulate transporter subcellular localization andor activity. In this study, the yeast two-hybrid system was used to identify a previously unknown 1607 base-pair cDNA whose polypeptide product named GT1BP1, binds to the Glutl C-terminus. The specificity of this interaction was examined using protein overlay assays. We have shown that four ammo acids at the Glutl C-terminus are required for binding to a PDZ domain within GT1BP1. However, GT1BP1 did not bind a putative PDZ recognition motif within the human Glut3 C-terminus. Furthermore, a valine to alanine change at the Glutl C-terminus, which disrupts some PDZ-protein interactions, did not abolish binding to GT1BP1. A GT1BP1 probe hybridized to a 1.6 kilobase RNA present in all rat tissues examined, with highest amounts in brain and kidney tissues. When Glutl and GT1BP1 were co-expressed in Xenopus laevis oocytes, the ratio of fully processed Glutl to core glycosylated Glutl was higher than in oocytes expressing Glutl alone. We conclude that 1)GT1BP1 contains a PDZ domain with unique binding specificity compared to previously reported PDZ domains, 2JGT1BP1 appears to exert a post-translational regulatory effect on Glutl in Xenopus oocytes, and 3JGT1BP1 mRNA expression parallels that of Glutl.