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A glucose transporter can mediate ribose uptake: definition of residues that confer substrate specificity in a sugar transporter.
- Source :
-
The Journal of biological chemistry [J Biol Chem] 2010 Sep 24; Vol. 285 (39), pp. 29721-8. Date of Electronic Publication: 2010 Jul 02. - Publication Year :
- 2010
-
Abstract
- Sugars, the major energy source for many organisms, must be transported across biological membranes. Glucose is the most abundant sugar in human plasma and in many other biological systems and has been the primary focus of sugar transporter studies in eukaryotes. We have previously cloned and characterized a family of glucose transporter genes from the protozoan parasite Leishmania. These transporters, called LmGT1, LmGT2, and LmGT3, are homologous to the well characterized glucose transporter (GLUT) family of mammalian glucose transporters. We have demonstrated that LmGT proteins are important for parasite viability. Here we show that one of these transporters, LmGT2, is a more effective carrier of the pentose sugar d-ribose than LmGT3, which has a 6-fold lower relative specificity (V(max)/K(m)) for ribose. A pair of threonine residues, located in the putative extracellular loops joining transmembrane helices 3 to 4 and 7 to 8, define a filter that limits ribose approaching the exofacial substrate binding pocket in LmGT3. When these threonines are substituted by alanine residues, as found in LmGT2, the LmGT3 permease acquires ribose permease activity that is similar to that of LmGT2. The location of these residues in hydrophilic loops supports recent suggestions that substrate recognition is separated from substrate binding and translocation in this important group of transporters.
- Subjects :
- Amino Acid Substitution
Animals
Binding Sites
Glucose Transport Proteins, Facilitative chemistry
Glucose Transport Proteins, Facilitative genetics
Humans
Leishmania mexicana chemistry
Leishmania mexicana genetics
Multigene Family physiology
Protein Structure, Secondary
Protozoan Proteins chemistry
Protozoan Proteins genetics
Sequence Homology, Amino Acid
Substrate Specificity
Glucose Transport Proteins, Facilitative metabolism
Leishmania mexicana metabolism
Protozoan Proteins metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 1083-351X
- Volume :
- 285
- Issue :
- 39
- Database :
- MEDLINE
- Journal :
- The Journal of biological chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 20601430
- Full Text :
- https://doi.org/10.1074/jbc.M110.106815