title: Six related nucleoside/nucleobase transporters from Trypanosoma brucei exhibit distinct biochemical functions.
abstract: Purine nucleoside and nucleobase transporters are of fundamental importance for Trypanosoma brucei and related kinetoplastid parasites because these protozoa are not able to synthesize purines de novo and must salvage the compounds from their hosts. In the studies reported here, we have identified a family of six clustered genes in T. brucei that encode nucleoside/nucleobase transporters. These genes, TbNT2/927, TbNT3, TbNT4, TbNT5, TbNT6, and TbNT7, have predicted amino acid sequences that show high identity to each other and to TbNT2, a P1 type nucleoside transporter recently identified in our laboratory. Expression in Xenopus laevis oocytes revealed that TbNT2/927, TbNT5, TbNT6, and TbNT7 are high affinity adenosine/inosine transporters with K(m) values of <5 microm. In addition, TbNT5, and to a limited degree TbNT6 and TbNT7, also mediate the uptake of the nucleobase hypoxanthine. Ribonuclease protection assays showed that mRNA from all of the six members of this gene family are expressed in the bloodstream stage of the T. brucei life cycle but that TbNT2/927 and TbNT5 mRNAs are also expressed in the insect stage of the life cycle. These results demonstrate that T. brucei expresses multiple purine transporters with distinct substrate specificities and different patterns of expression during the parasite life cycle.
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon 97201, USA. sanchezm@ohsu.edu
authors.forename: Marco A
authors.initials: MA
authors.lastname: Sanchez
authors.forename: Rob
authors.initials: R
authors.lastname: Tryon
authors.forename: Joy
authors.initials: J
authors.lastname: Green
authors.forename: Ilja
authors.initials: I
authors.lastname: Boor
authors.forename: Scott M
authors.initials: SM
authors.lastname: Landfear
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism; D018105:DNA, Kinetoplast / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009696:Nucleic Acids / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D016366:Open Reading Frames; D020033:Protein Isoforms; D018075:RNA, Complementary / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013997:Time Factors; D014346:Trypanosoma brucei brucei / Q000378:metabolism*; D014981:Xenopus / Q000378:metabolism
chemical_list: D018105:DNA, Kinetoplast; D009696:Nucleic Acids; D020033:Protein Isoforms; D018075:RNA, Complementary; D012333:RNA, Messenger; D004247:DNA; D012260:Ribonucleases