Complementation of a glucose transporter mutant of Schizosaccharomyces pombe by a novel Trypanosoma brucei gene

The African trypanosome Trypanosoma brucei has a digenetic life cycle that involves the insect vector and the mammalian host. This is underscored by b iochemical switches in its nutritional requirements. In the insect vector, the parasite relies on amino acid catabolism, but in the mammalian host, it derives its energy exclusively from blood glucose. Glucose transport is fa cilitated, and constitutes the rate-limiting step in ATP synthesis. Here, w e report the cloning of a novel glucose transporter-related gene by heterol ogous screening of a lambda EMBL4 genomic library of T. brucei EATRO 164 us ing a rat liver glucose transporter cDNA clone. Genomic analysis shows that the gene is present as a single copy within the parasite genome. The gene encodes a protein with an estimated molecular mass of 55.9 kDa, which share s only segmental homology with members of the glucose transporter superfami ly, Several potential post-translational modification sites including phosp horylation, N-glycosylation, and cotranslational myristoylation sites also punctuate the sequence. It is distinguished from classical transporter prot eins by the absence of putative hydrophobic membrane-spanning domains. Howe ver, this protein was capable of complementing Schizosaccharomyces pombe gl ucose transporter mutants. The rescued phenotype conferred the ability of t he cells to grow on a broad range of sugars, both monosaccharides and disac charides. The kinetics of glucose uptake reflected those in T, brucei, In a ddition to complementation in yeast, we also showed that the gene enhanced glucose uptake in cultured mammalian cells.