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Molecular Pharmacology

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Research ArticleArticle

A Novel Proton-Dependent Nucleoside Transporter, CeCNT3, fromCaenorhabditis elegans

Guangqing Xiao, Juan Wang, Tonje Tangen and Kathleen M. Giacomini
Molecular Pharmacology February 2001, 59 (2) 339-348; DOI: https://doi.org/10.1124/mol.59.2.339
Guangqing Xiao
Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, San Francisco, California
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Juan Wang
Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, San Francisco, California
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Tonje Tangen
Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, San Francisco, California
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Kathleen M. Giacomini
Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco, San Francisco, California
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Abstract

In this study, we describe the cloning and characterization of a proton-dependent, broadly selective nucleoside transporter fromCaenorhabditis elegans. Recently, we constructed a broadly selective nucleoside transporter which accepts both purine and pyrimidine nucleosides. Based on these studies, we hypothesized that CNTs with novel substrate selectivities exist in nature and that a CNT homolog in the C. elegans genomic database may function as a broadly selective nucleoside transporter. We cloned the cDNA for this transporter, termed CeCNT3 because of its broad selectivity, using polymerase chain reaction-based methods. CeCNT3 is predicted to have 575 amino acid residues (63.4 kDa) with 11 to 14 putative transmembrane domains and exhibits ∼30% identity to members of the mammalian CNT family. This transporter exhibits a novel substrate selectivity, transporting a wide range of purine and pyrimidine nucleosides (inosine, guanosine, adenosine, uridine, and thymidine) but not cytidine. The apparent K m values for inosine and thymidine are 15.2 ± 5.3 μM and 11.0 ± 2.4 μM, respectively. Kinetic studies demonstrate that purine and pyrimidine nucleosides share a common recognition site in the transporter. In contrast to all known members of the mammalian CNT family, CeCNT3-mediated transport of nucleosides is proton-, but not sodium-, dependent. Mutation of tyrosine 332 in CeCNT3 decreased both the maximum uptake rate and apparent K m of thymidine, suggesting that this residue is in the domain of nucleoside recognition and translocation. The broad nucleoside specificity of CeCNT3 may be explained by this and other residues that restrict purine and pyrimidine nucleoside uptake and that discriminate among pyrimidine nucleosides.

Footnotes

    • Received May 11, 2000.
    • Accepted October 18, 2000.
  • Send reprint requests to: Kathleen M. Giacomini, Ph.D., Department of Biopharmaceutical Sciences, Box 0446, University of California, San Francisco, California. E-mail:kmg{at}itsa.ucsf.edu

  • This study was supported by National Institutes of Health Grant GM42230.

  • The American Society for Pharmacology and Experimental Therapeutics
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Molecular Pharmacology: 59 (2)
Molecular Pharmacology
Vol. 59, Issue 2
1 Feb 2001
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Research ArticleArticle

A Novel Proton-Dependent Nucleoside Transporter, CeCNT3, fromCaenorhabditis elegans

Guangqing Xiao, Juan Wang, Tonje Tangen and Kathleen M. Giacomini
Molecular Pharmacology February 1, 2001, 59 (2) 339-348; DOI: https://doi.org/10.1124/mol.59.2.339

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Research ArticleArticle

A Novel Proton-Dependent Nucleoside Transporter, CeCNT3, fromCaenorhabditis elegans

Guangqing Xiao, Juan Wang, Tonje Tangen and Kathleen M. Giacomini
Molecular Pharmacology February 1, 2001, 59 (2) 339-348; DOI: https://doi.org/10.1124/mol.59.2.339
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