Erythrocytic Adenosine Monophosphate as an Alternative Purine Source in Plasmodium falciparum

María B Cassera,Keith Z Hazleton,Paul M Riegelhaupt,Emilio F Merino,Minkui Luo,Myles H Akabas,Vern L Schramm

doi:10.1074/jbc.m804497200

María B Cassera, Keith Z Hazleton + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m804497200

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Abstract

Plasmodium falciparum is a purine auxotroph, salvaging purines from erythrocytes for synthesis of RNA and DNA. Hypoxanthine is the key precursor for purine metabolism in Plasmodium. Inhibition of hypoxanthine-forming reactions in both erythrocytes and parasites is lethal to cultured P. falciparum. We observed that high concentrations of adenosine can rescue cultured parasites from purine nucleoside phosphorylase and adenosine deaminase blockade but not when erythrocyte adenosine kinase is also inhibited. P. falciparum lacks adenosine kinase but can salvage AMP synthesized in the erythrocyte cytoplasm to provide purines when both human and Plasmodium purine nucleoside phosphorylases and adenosine deaminases are inhibited. Transport studies in Xenopus laevis oocytes expressing the P. falciparum nucleoside transporter PfNT1 established that this transporter does not transport AMP. These metabolic patterns establish the existence of a novel nucleoside monophosphate transport pathway in P. falciparum.

Highlights

P. falciparum is a purine auxotroph, salvaging host cell purines for synthesis of cofactors and nucleic acids [4, 5]
P. falciparum cell growth and division demands robust purine salvage, in particular adenosine, because the parasite contains the most (A ϩ T)-rich genome sequenced to date (ϳ80%)
We found that high concentrations of adenosine rescue P. falciparum from PNP inhibition or from combined PNP and ADA inhibition

Summary

Introduction

P. falciparum is a purine auxotroph, salvaging host cell purines for synthesis of cofactors and nucleic acids [4, 5]. Adenosine is efficiently salvaged by adenosine kinase (hAK). In P. falciparum, adenosine is salvaged by conversion to hypoxanthine using adenosine deaminase (PfADA) and purine nucleoside phosphorylase (PfPNP). P. falciparum cell growth and division demands robust purine salvage, in particular adenosine, because the parasite contains the most (A ϩ T)-rich genome sequenced to date (ϳ80%). Inhibition of the purine salvage pathway with transition state analogue inhibitors of both human and Plasmodium PNP, such as immucillin-H (ImmH), is lethal for P. falciparum in vitro [9]. Miltenyi Biotec), washed pathway in P. falciparum, we have characterized adenosine in purine-free medium to remove excess hypoxanthine, and inocmetabolism in this parasite. We demonstrate a previously ulated into freshly drawn erythrocytes that had been washed and unreported salvage pathway for adenosine in P. falciparum that resuspended in purine-free medium. Erythrocytes were obtained involves synthesis of AMP by human erythrocyte AK followed from healthy donors under the Committee on Clinical Investigaby uptake of AMP from the erythrocyte cytosol

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