Malaria parasite type 4 equilibrative nucleoside transporters (ENT4) are purine transporters with distinct substrate specificity

I. J. Frame, Emilio F. Merino, Vern L. Schramm, María B. Cassera, Myles Akabas

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Malaria, caused by Plasmodia parasites, affects hundreds of millions of people. As purine auxotrophs, Plasmodia use transporters to import host purines for subsequent metabolism by the purine salvage pathway. Thus purine transporters are attractive drug targets. All sequenced Plasmodia genomes encode four ENTs (equilibrative nucleoside transporters). During the pathogenic intraerythrocytic stages, ENT1 is a major route of purine nucleoside/nucleobase transport. Another plasma membrane purine transporter exists because Plasmodium falciparum ENT1-knockout parasites survive at supraphysiological purine concentrations. The other three ENTs have not been characterized functionally. Codon-optimized Pf- (P. falciparum) and Pv- (Plasmodium vivax) ENT4 were expressed in Xenopus laevis oocytes and substrate transport was determined with radiolabelled substrates. ENT4 transported adenine and 2′-deoxyadenosine at the highest rate, with millimolar-range apparent affinity. ENT4-expressing oocytes did not accumulate hypoxanthine, a key purine salvage pathway substrate, or AMP. Micromolar concentrations of the plant hormone cytokinin compounds inhibited both PfENT4 and PvENT4. In contrast with PfENT1, ENT4 interacted with the immucillin compounds in the millimolar range and was inhibited by 10 μMdipyridamole. Thus ENT4 is a purine transporter with unique substrate and inhibitor specificity. Its role in parasite physiology remains uncertain, but is likely to be significant because of the strong conservation of ENT4 homologues in Plasmodia genomes.

Original languageEnglish (US)
Pages (from-to)179-190
Number of pages12
JournalBiochemical Journal
Volume446
Issue number2
DOIs
StatePublished - Sep 1 2012

Fingerprint

Nucleoside Transport Proteins
Substrate Specificity
Malaria
Parasites
Substrates
Plasmodium
Salvaging
Plasmodium falciparum
Oocytes
Genes
Plasmodium malariae
Genome
Purine Nucleosides
Plasmodium vivax
Cytokinins
Purines
Hypoxanthine
Plant Growth Regulators
Membrane Transport Proteins
Physiology

Keywords

  • Adenine
  • Adenosine
  • Equilibrative nucloside transporter 4 (ENT4)
  • Immucillin
  • Plasmodium
  • Purine transporter

ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Molecular Biology

Cite this

Malaria parasite type 4 equilibrative nucleoside transporters (ENT4) are purine transporters with distinct substrate specificity. / Frame, I. J.; Merino, Emilio F.; Schramm, Vern L.; Cassera, María B.; Akabas, Myles.

In: Biochemical Journal, Vol. 446, No. 2, 01.09.2012, p. 179-190.

Research output: Contribution to journalArticle

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abstract = "Malaria, caused by Plasmodia parasites, affects hundreds of millions of people. As purine auxotrophs, Plasmodia use transporters to import host purines for subsequent metabolism by the purine salvage pathway. Thus purine transporters are attractive drug targets. All sequenced Plasmodia genomes encode four ENTs (equilibrative nucleoside transporters). During the pathogenic intraerythrocytic stages, ENT1 is a major route of purine nucleoside/nucleobase transport. Another plasma membrane purine transporter exists because Plasmodium falciparum ENT1-knockout parasites survive at supraphysiological purine concentrations. The other three ENTs have not been characterized functionally. Codon-optimized Pf- (P. falciparum) and Pv- (Plasmodium vivax) ENT4 were expressed in Xenopus laevis oocytes and substrate transport was determined with radiolabelled substrates. ENT4 transported adenine and 2′-deoxyadenosine at the highest rate, with millimolar-range apparent affinity. ENT4-expressing oocytes did not accumulate hypoxanthine, a key purine salvage pathway substrate, or AMP. Micromolar concentrations of the plant hormone cytokinin compounds inhibited both PfENT4 and PvENT4. In contrast with PfENT1, ENT4 interacted with the immucillin compounds in the millimolar range and was inhibited by 10 μMdipyridamole. Thus ENT4 is a purine transporter with unique substrate and inhibitor specificity. Its role in parasite physiology remains uncertain, but is likely to be significant because of the strong conservation of ENT4 homologues in Plasmodia genomes.",
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