PfNT2, a Permease of the Equilibrative Nucleoside Transporter Family in the Endoplasmic Reticulum of Plasmodium falciparum

Megan J Downie,Kamal El Bissati,April M Bobenchik,Laura Nic Lochlainn,Alexander Amerik,Rachel Zufferey,Kiaran Kirk,Choukri Ben Mamoun

doi:10.1074/jbc.m110.118489

Megan J Downie, Kamal El Bissati + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m110.118489

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Abstract

The survival and proliferation of the obligate intracellular malaria parasite Plasmodium falciparum require salvage of essential purines from the host. Genetic studies have previously shown that the parasite plasma membrane purine permease, PfNT1, plays an essential function in the transport of all naturally occurring purine nucleosides and nucleobases across the parasite plasma membrane. Here, we describe an intracellular permease, PfNT2. PfNT2 is, like PfNT1, a member of the equilibrative nucleoside transporter family. Confocal and immunoelectron microscopic analyses of transgenic parasites harboring green fluorescent protein- or hemagglutinin-tagged PfNT2 demonstrated endoplasmic reticulum localization. This localization was confirmed by colocalization with the endoplasmic reticulum marker PfBiP. Using yeast as a surrogate system, we show that targeting PfNT2 to the plasma membrane of fui1Delta cells lacking the plasma membrane nucleoside transporter Fui1 confers sensitivity to the toxic nucleoside analog 5-fluorouridine. This study provides the first evidence of an intracellular purine permease in apicomplexan parasites and suggests a novel biological function for the parasite endoplasmic reticulum during malaria infection.

Highlights

Plasmodium parasites, the causative agents of malaria, are incapable of synthesizing the purine ring de novo
Searches of Plasmodium genome sequence data with the sequences of known protozoan and mammalian nucleoside transporters led to the identification of a Plasmodium protein, PfNT1 [9, 10], which is a member of the equilibrative nucleoside transporter (ENT)3 family and is localized to the parasite plasma membrane [11]
The localization of PfNT2 to the endoplasmic reticulum (ER), unexpected, was not unprecedented, as several nucleoside transporters are known to function as intracellular transporters

Summary

Introduction

Plasmodium parasites, the causative agents of malaria, are incapable of synthesizing the purine ring de novo. Studies on parasites “isolated” from their host cell have shown that both purine and pyrimidine nucleosides and nucleobases are transported across this membrane via a rapid, low affinity, equilibrative process [7, 8]. Searches of Plasmodium genome sequence data with the sequences of known protozoan and mammalian nucleoside transporters led to the identification of a Plasmodium protein, PfNT1 [9, 10], which is a member of the equilibrative nucleoside transporter (ENT)3 family and is localized to the parasite plasma membrane [11].

Results

Conclusion