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Mechanistic basis for multidrug resistance and collateral drug sensitivity conferred to the malaria parasite by polymorphisms in PfMDR1 and PfCRT. PLoS Biol 2022; 20:e3001616. [PMID: 35507548 PMCID: PMC9067703 DOI: 10.1371/journal.pbio.3001616] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 03/31/2022] [Indexed: 01/16/2023] Open
Abstract
Polymorphisms in the Plasmodium falciparum multidrug resistance protein 1 (pfmdr1) gene and the Plasmodium falciparum chloroquine resistance transporter (pfcrt) gene alter the malaria parasite’s susceptibility to most of the current antimalarial drugs. However, the precise mechanisms by which PfMDR1 contributes to multidrug resistance have not yet been fully elucidated, nor is it understood why polymorphisms in pfmdr1 and pfcrt that cause chloroquine resistance simultaneously increase the parasite’s susceptibility to lumefantrine and mefloquine—a phenomenon known as collateral drug sensitivity. Here, we present a robust expression system for PfMDR1 in Xenopus oocytes that enables direct and high-resolution biochemical characterizations of the protein. We show that wild-type PfMDR1 transports diverse pharmacons, including lumefantrine, mefloquine, dihydroartemisinin, piperaquine, amodiaquine, methylene blue, and chloroquine (but not the antiviral drug amantadine). Field-derived mutant isoforms of PfMDR1 differ from the wild-type protein, and each other, in their capacities to transport these drugs, indicating that PfMDR1-induced changes in the distribution of drugs between the parasite’s digestive vacuole (DV) and the cytosol are a key driver of both antimalarial resistance and the variability between multidrug resistance phenotypes. Of note, the PfMDR1 isoforms prevalent in chloroquine-resistant isolates exhibit reduced capacities for chloroquine, lumefantrine, and mefloquine transport. We observe the opposite relationship between chloroquine resistance-conferring mutations in PfCRT and drug transport activity. Using our established assays for characterizing PfCRT in the Xenopus oocyte system and in live parasite assays, we demonstrate that these PfCRT isoforms transport all 3 drugs, whereas wild-type PfCRT does not. We present a mechanistic model for collateral drug sensitivity in which mutant isoforms of PfMDR1 and PfCRT cause chloroquine, lumefantrine, and mefloquine to remain in the cytosol instead of sequestering within the DV. This change in drug distribution increases the access of lumefantrine and mefloquine to their primary targets (thought to be located outside of the DV), while simultaneously decreasing chloroquine’s access to its target within the DV. The mechanistic insights presented here provide a basis for developing approaches that extend the useful life span of antimalarials by exploiting the opposing selection forces they exert upon PfCRT and PfMDR1.
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Monteiro Júnior JC, Krüger A, Palmisano G, Wrenger C. Transporter-Mediated Solutes Uptake as Drug Target in Plasmodium falciparum. Front Pharmacol 2022; 13:845841. [PMID: 35370717 PMCID: PMC8965513 DOI: 10.3389/fphar.2022.845841] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Accepted: 02/09/2022] [Indexed: 02/05/2023] Open
Abstract
Malaria remains a public health problem with still more than half a million deaths annually. Despite ongoing efforts of many countries, malaria elimination has been difficult due to emerging resistances against most traditional drugs, including artemisinin compounds - the most potent antimalarials currently available. Therefore, the discovery and development of new drugs with novel mechanisms of action to circumvent resistances is urgently needed. In this sense, one of the most promising areas is the exploration of transport proteins. Transporters mediate solute uptake for intracellular parasite proliferation and survival. Targeting transporters can exploit these processes to eliminate the parasite. Here, we focus on transporters of the Plasmodium falciparum-infected red blood cell studied as potential biological targets and discuss published drugs directed at them.
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Affiliation(s)
- Júlio César Monteiro Júnior
- Unit for Drug Discovery, Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - Arne Krüger
- Unit for Drug Discovery, Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - Giuseppe Palmisano
- GlycoProteomics Laboratory, Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - Carsten Wrenger
- Unit for Drug Discovery, Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
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3
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An Uninvited Seat at the Dinner Table: How Apicomplexan Parasites Scavenge Nutrients from the Host. Microorganisms 2021; 9:microorganisms9122592. [PMID: 34946193 PMCID: PMC8707601 DOI: 10.3390/microorganisms9122592] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 12/10/2021] [Accepted: 12/13/2021] [Indexed: 12/24/2022] Open
Abstract
Obligate intracellular parasites have evolved a remarkable assortment of strategies to scavenge nutrients from the host cells they parasitize. Most apicomplexans form a parasitophorous vacuole (PV) within the invaded cell, a replicative niche within which they survive and multiply. As well as providing a physical barrier against host cell defense mechanisms, the PV membrane (PVM) is also an important site of nutrient uptake that is essential for the parasites to sustain their metabolism. This means nutrients in the extracellular milieu are separated from parasite metabolic machinery by three different membranes, the host plasma membrane, the PVM, and the parasite plasma membrane (PPM). In order to facilitate nutrient transport from the extracellular environment into the parasite itself, transporters on the host cell membrane of invaded cells can be modified by secreted and exported parasite proteins to maximize uptake of key substrates to meet their metabolic demand. To overcome the second barrier, the PVM, apicomplexan parasites secrete proteins contained in the dense granules that remodel the vacuole and make the membrane permissive to important nutrients. This bulk flow of host nutrients is followed by a more selective uptake of substrates at the PPM that is operated by specific transporters of this third barrier. In this review, we recapitulate and compare the strategies developed by Apicomplexa to scavenge nutrients from their hosts, with particular emphasis on transporters at the parasite plasma membrane and vacuolar solute transporters on the parasite intracellular digestive organelle.
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Molbaek K, Tejada M, Ricke CH, Scharff-Poulsen P, Ellekvist P, Helix-Nielsen C, Kumar N, Klaerke DA, Pedersen PA. Purification and initial characterization of Plasmodium falciparum K + channels, PfKch1 and PfKch2 produced in Saccharomyces cerevisiae. Microb Cell Fact 2020; 19:183. [PMID: 32957994 PMCID: PMC7507820 DOI: 10.1186/s12934-020-01437-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 09/09/2020] [Indexed: 02/07/2023] Open
Abstract
Resistance towards known antimalarial drugs poses a significant problem, urging for novel drugs that target vital proteins in the malaria parasite Plasmodium falciparum. However, recombinant production of malaria proteins is notoriously difficult. To address this, we have investigated two putative K+ channels, PfKch1 and PfKch2, identified in the P. falciparum genome. We show that PfKch1 and PfKch2 and a C-terminally truncated version of PfKch1 (PfKch11−1094) could indeed be functionally expressed in vivo, since a K+-uptake deficient Saccharomyces cerevisiae strain was complemented by the P. falciparum cDNAs. PfKch11−1094-GFP and GFP-PfKch2 fusion proteins were overexpressed in yeast, purified and reconstituted in lipid bilayers to determine their electrophysiological activity. Single channel conductance amounted to 16 ± 1 pS for PfKch11−1094-GFP and 28 ± 2 pS for GFP-PfKch2. We predicted regulator of K+-conductance (RCK) domains in the C-terminals of both channels, and we accordingly measured channel activity in the presence of Ca2+.
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Affiliation(s)
- Karen Molbaek
- Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg, 1870, Denmark.,Department of Biology, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Maria Tejada
- Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg, 1870, Denmark
| | - Christina Hoeier Ricke
- Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg, 1870, Denmark
| | - Peter Scharff-Poulsen
- Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg, 1870, Denmark
| | - Peter Ellekvist
- Medical Department, Herlev-Gentofte Hospital, Herlev, 2730, Denmark
| | - Claus Helix-Nielsen
- Aquaporin A/S, Kgs Lyngby, 2800, Denmark.,Department of Environmental Engineering, Technical University of Denmark, Kgs Lyngby, 2800, Denmark.,University of Maribor, Laboratory for Water Biophysics and Membrane Technology, Maribor, 2000, Slovenia
| | - Nirbhay Kumar
- Department of Global Health, Milken Institute School of Public Health, George Washington University, Washington DC, 20052-0066, USA
| | - Dan A Klaerke
- Department of Veterinary and Animal Sciences, University of Copenhagen, Frederiksberg, 1870, Denmark.
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5
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Shafik SH, Cobbold SA, Barkat K, Richards SN, Lancaster NS, Llinás M, Hogg SJ, Summers RL, McConville MJ, Martin RE. The natural function of the malaria parasite's chloroquine resistance transporter. Nat Commun 2020; 11:3922. [PMID: 32764664 PMCID: PMC7413254 DOI: 10.1038/s41467-020-17781-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 07/15/2020] [Indexed: 01/27/2023] Open
Abstract
The Plasmodium falciparum chloroquine resistance transporter (PfCRT) is a key contributor to multidrug resistance and is also essential for the survival of the malaria parasite, yet its natural function remains unresolved. We identify host-derived peptides of 4-11 residues, varying in both charge and composition, as the substrates of PfCRT in vitro and in situ, and show that PfCRT does not mediate the non-specific transport of other metabolites and/or ions. We find that drug-resistance-conferring mutations reduce both the peptide transport capacity and substrate range of PfCRT, explaining the impaired fitness of drug-resistant parasites. Our results indicate that PfCRT transports peptides from the lumen of the parasite's digestive vacuole to the cytosol, thereby providing a source of amino acids for parasite metabolism and preventing osmotic stress of this organelle. The resolution of PfCRT's native substrates will aid the development of drugs that target PfCRT and/or restore the efficacy of existing antimalarials.
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Affiliation(s)
- Sarah H Shafik
- Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Simon A Cobbold
- Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC, 3052, Australia
| | - Kawthar Barkat
- Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Sashika N Richards
- Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Nicole S Lancaster
- Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Manuel Llinás
- Department of Biochemistry and Molecular Biology, Department of Chemistry, and Huck Center for Malaria Research, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Simon J Hogg
- Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Robert L Summers
- Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia
| | - Malcolm J McConville
- Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC, 3052, Australia
| | - Rowena E Martin
- Research School of Biology, The Australian National University, Canberra, ACT, 2601, Australia.
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Sosa Y, Deniskin R, Frame IJ, Steiginga MS, Bandyopadhyay D, Graybill TL, Kallal LA, Ouellette MT, Pope AJ, Widdowson KL, Young RJ, Akabas MH. Identification via a Parallel Hit Progression Strategy of Improved Small Molecule Inhibitors of the Malaria Purine Uptake Transporter that Inhibit Plasmodium falciparum Parasite Proliferation. ACS Infect Dis 2019; 5:1738-1753. [PMID: 31373203 DOI: 10.1021/acsinfecdis.9b00168] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Emerging resistance to current antimalarial medicines underscores the importance of identifying new drug targets and novel compounds. Malaria parasites are purine auxotrophic and import purines via the Plasmodium falciparum equilibrative nucleoside transporter type 1 (PfENT1). We previously showed that PfENT1 inhibitors block parasite proliferation in culture. Our goal was to identify additional, possibly more optimal chemical starting points for a drug discovery campaign. We performed a high throughput screen (HTS) of GlaxoSmithKline's 1.8 million compound library with a yeast-based assay to identify PfENT1 inhibitors. We used a parallel progression strategy for hit validation and expansion, with an emphasis on chemical properties in addition to potency. In one arm, the most active hits were tested for human cell toxicity; 201 had minimal toxicity. The second arm, hit expansion, used a scaffold-based substructure search with the HTS hits as templates to identify over 2000 compounds; 123 compounds had activity. Of these 324 compounds, 175 compounds inhibited proliferation of P. falciparum parasite strain 3D7 with IC50 values between 0.8 and ∼180 μM. One hundred forty-two compounds inhibited PfENT1 knockout (pfent1Δ) parasite growth, indicating they also hit secondary targets. Thirty-two hits inhibited growth of 3D7 but not pfent1Δ parasites. Thus, PfENT1 inhibition was sufficient to block parasite proliferation. Therefore, PfENT1 may be a viable target for antimalarial drug development. Six compounds with novel chemical scaffolds were extensively characterized in yeast-, parasite-, and human-erythrocyte-based assays. The inhibitors showed similar potencies against drug sensitive and resistant P. falciparum strains. They represent attractive starting points for development of novel antimalarial drugs.
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Affiliation(s)
| | | | | | - Matthew S. Steiginga
- Platform Technology & Science and Discovery Partners in Academia, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
| | - Deepak Bandyopadhyay
- Platform Technology & Science and Discovery Partners in Academia, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
| | - Todd L. Graybill
- Platform Technology & Science and Discovery Partners in Academia, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
| | - Lorena A. Kallal
- Platform Technology & Science and Discovery Partners in Academia, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
| | - Michael T. Ouellette
- Platform Technology & Science and Discovery Partners in Academia, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
| | - Andrew J. Pope
- Platform Technology & Science and Discovery Partners in Academia, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
| | - Katherine L. Widdowson
- Platform Technology & Science and Discovery Partners in Academia, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
| | - Robert J. Young
- Platform Technology & Science and Discovery Partners in Academia, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, Pennsylvania 19426, United States
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7
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Nishtala SN, Arora A, Reyes J, Akabas MH. Accessibility of substituted cysteines in TM2 and TM10 transmembrane segments in the Plasmodium falciparum equilibrative nucleoside transporter PfENT1. J Biol Chem 2019; 294:1924-1935. [PMID: 30541922 DOI: 10.1074/jbc.ra118.006547] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 11/30/2018] [Indexed: 11/06/2022] Open
Abstract
Infection with Plasmodium species parasites causes malaria. Plasmodium parasites are purine auxotrophic. They import purines via an equilibrative nucleoside transporter (ENT). In P. falciparum, the most virulent species, the equilibrative nucleoside transporter 1 (PfENT1) represents the primary purine uptake pathway. This transporter is a potential target for the development of antimalarial drugs. In the absence of a high-resolution structure for either PfENT1 or a homologous ENT, we used the substituted cysteine accessibility method (SCAM) to investigate the membrane-spanning domain structure of PfENT1 to identify potential inhibitor-binding sites. We previously used SCAM to identify water-accessible residues that line the permeation pathway in transmembrane segment 11 (TM11). TM2 and TM10 lie adjacent to TM11 in an ab initio model of a homologous Leishmania donovani nucleoside transporter. To identify TM2 and TM10 residues in PfENT1 that are at least transiently on the water-accessible transporter surface, we assayed the reactivity of single cysteine-substitution mutants with three methanethiosulfonate (MTS) derivatives. Cysteines substituted for 12 of 14 TM2 segment residues reacted with MTS-ethyl-ammonium-biotin (MTSEA-biotin). At eight positions, MTSEA-biotin inhibited transport, and at four positions substrate transport was potentiated. On an α helical wheel projection of TM2, the four positions where potentiation occurred were located in a cluster on one side of the helix. In contrast, although MTSEA-biotin inhibited 9 of 10 TM10 cysteine-substituted mutants, the reactive residues did not form a pattern consistent with either an α helix or β sheet. These results may help identify the binding site(s) of PfENT1 inhibitors.
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Affiliation(s)
| | - Avish Arora
- From the Departments of Physiology and Biophysics
| | - Jorge Reyes
- From the Departments of Physiology and Biophysics
| | - Myles H Akabas
- From the Departments of Physiology and Biophysics, .,Neuroscience, and.,Medicine, Albert Einstein College of Medicine, Bronx, New York 10461
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Hapuarachchi SV, Cobbold SA, Shafik SH, Dennis ASM, McConville MJ, Martin RE, Kirk K, Lehane AM. The Malaria Parasite's Lactate Transporter PfFNT Is the Target of Antiplasmodial Compounds Identified in Whole Cell Phenotypic Screens. PLoS Pathog 2017; 13:e1006180. [PMID: 28178359 PMCID: PMC5298231 DOI: 10.1371/journal.ppat.1006180] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 01/11/2017] [Indexed: 11/19/2022] Open
Abstract
In this study the ‘Malaria Box’ chemical library comprising 400 compounds with antiplasmodial activity was screened for compounds that perturb the internal pH of the malaria parasite, Plasmodium falciparum. Fifteen compounds induced an acidification of the parasite cytosol. Two of these did so by inhibiting the parasite’s formate nitrite transporter (PfFNT), which mediates the H+-coupled efflux from the parasite of lactate generated by glycolysis. Both compounds were shown to inhibit lactate transport across the parasite plasma membrane, and the transport of lactate by PfFNT expressed in Xenopus laevis oocytes. PfFNT inhibition caused accumulation of lactate in parasitised erythrocytes, and swelling of both the parasite and parasitised erythrocyte. Long-term exposure of parasites to one of the inhibitors gave rise to resistant parasites with a mutant form of PfFNT that showed reduced inhibitor sensitivity. This study provides the first evidence that PfFNT is a druggable antimalarial target. The emergence and spread of Plasmodium falciparum strains resistant to leading antimalarial drugs has intensified the need to discover and develop drugs that kill the parasite via new mechanisms. Here we screened compounds that are known to inhibit P. falciparum growth for their effects on the pH inside the parasite. We identified fifteen compounds that decrease the pH inside the parasite, and determined the mechanism by which two of these, MMV007839 and MMV000972, disrupt pH and kill the parasite. The two compounds were found to inhibit the P. falciparum formate nitrite transporter (PfFNT), a transport protein that is located on the parasite surface and that serves to remove the waste product lactic acid from the parasite. The compounds inhibited both the H+-coupled transport of lactate across the parasite plasma membrane and the transport of lactate by PfFNT expressed in Xenopus oocytes. In addition to disrupting pH, PfFNT inhibition led to a build-up of lactate in the parasite-infected red blood cell and the swelling of both the parasite and the infected red blood cell. Exposing parasites to MMV007839 over a prolonged time period gave rise to resistant parasites with a mutant form of PfFNT that was less sensitive to the compound. This study validates PfFNT as a novel antimalarial drug target.
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Affiliation(s)
| | - Simon A Cobbold
- Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC, Australia
| | - Sarah H Shafik
- Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Adelaide S M Dennis
- Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Malcolm J McConville
- Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, VIC, Australia
| | - Rowena E Martin
- Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Kiaran Kirk
- Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Adele M Lehane
- Research School of Biology, Australian National University, Canberra, ACT, Australia
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9
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Arora A, Deniskin R, Sosa Y, Nishtala SN, Henrich PP, Kumar TRS, Fidock DA, Akabas MH. Substrate and Inhibitor Specificity of the Plasmodium berghei Equilibrative Nucleoside Transporter Type 1. Mol Pharmacol 2016; 89:678-85. [PMID: 27048953 DOI: 10.1124/mol.115.101386] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Accepted: 04/04/2016] [Indexed: 12/22/2022] Open
Abstract
Malaria is a critical public health issue in the tropical world, causing extensive morbidity and mortality. Infection by unicellular, obligate intracellular Plasmodium parasites causes malaria. The emergence of resistance to current antimalarial drugs necessitates the development of novel therapeutics. A potential novel drug target is the purine import transporter. Because Plasmodium parasites are purine auxotrophic, they must import purines from their host to fulfill metabolic requirements. They import purines via equilibrative nucleoside transporter 1 (ENT1) homologs. Recently, we used a yeast-based high-throughput screen to identify inhibitors of the P. falciparum ENT1 (PfENT1) that kill P. falciparum parasites in culture. P. berghei infection of mice is an animal model for human malaria. Because P. berghei ENT1 (PbENT1) shares only 60% amino acid sequence identity with PfENT1, we sought to characterize PbENT1 and its sensitivity to our PfENT1 inhibitors. We expressed PbENT1 in purine auxotrophic yeast and used radiolabeled substrate uptake to characterize its function. We showed that PbENT1 transports both purines and pyrimidines. It preferred nucleosides compared with nucleobases. Inosine (IC50 = 3.7 µM) and guanosine (IC50 = 21.3 µM) had the highest affinities. Our recently discovered PfENT1 inhibitors were equally effective against both PbENT1- and PfENT1-mediated purine uptake. The PfENT1 inhibitors are at least 10-fold more potent against PfENT1 than human hENT1. They kill P. berghei parasites in 24-hour ex vivo culture. Thus, the P. berghei murine malaria model may be useful to evaluate the efficacy of PfENT1 inhibitors in vivo and their therapeutic potential for treatment of malaria.
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Affiliation(s)
- Avish Arora
- Departments of Physiology and Biophysics (A.A., R.D., Y.S., S.N.N., M.H.A.) and Neuroscience and Medicine (M.H.A.), Albert Einstein College of Medicine, Bronx, New York; and Departments Microbiology and Immunology (P.P.H., T.R.S.K., D.A.F.) and Medicine (D.A.F.), Columbia University Medical Center, New York, New York
| | - Roman Deniskin
- Departments of Physiology and Biophysics (A.A., R.D., Y.S., S.N.N., M.H.A.) and Neuroscience and Medicine (M.H.A.), Albert Einstein College of Medicine, Bronx, New York; and Departments Microbiology and Immunology (P.P.H., T.R.S.K., D.A.F.) and Medicine (D.A.F.), Columbia University Medical Center, New York, New York
| | - Yvett Sosa
- Departments of Physiology and Biophysics (A.A., R.D., Y.S., S.N.N., M.H.A.) and Neuroscience and Medicine (M.H.A.), Albert Einstein College of Medicine, Bronx, New York; and Departments Microbiology and Immunology (P.P.H., T.R.S.K., D.A.F.) and Medicine (D.A.F.), Columbia University Medical Center, New York, New York
| | - Sita Nirupama Nishtala
- Departments of Physiology and Biophysics (A.A., R.D., Y.S., S.N.N., M.H.A.) and Neuroscience and Medicine (M.H.A.), Albert Einstein College of Medicine, Bronx, New York; and Departments Microbiology and Immunology (P.P.H., T.R.S.K., D.A.F.) and Medicine (D.A.F.), Columbia University Medical Center, New York, New York
| | - Philipp P Henrich
- Departments of Physiology and Biophysics (A.A., R.D., Y.S., S.N.N., M.H.A.) and Neuroscience and Medicine (M.H.A.), Albert Einstein College of Medicine, Bronx, New York; and Departments Microbiology and Immunology (P.P.H., T.R.S.K., D.A.F.) and Medicine (D.A.F.), Columbia University Medical Center, New York, New York
| | - T R Santha Kumar
- Departments of Physiology and Biophysics (A.A., R.D., Y.S., S.N.N., M.H.A.) and Neuroscience and Medicine (M.H.A.), Albert Einstein College of Medicine, Bronx, New York; and Departments Microbiology and Immunology (P.P.H., T.R.S.K., D.A.F.) and Medicine (D.A.F.), Columbia University Medical Center, New York, New York
| | - David A Fidock
- Departments of Physiology and Biophysics (A.A., R.D., Y.S., S.N.N., M.H.A.) and Neuroscience and Medicine (M.H.A.), Albert Einstein College of Medicine, Bronx, New York; and Departments Microbiology and Immunology (P.P.H., T.R.S.K., D.A.F.) and Medicine (D.A.F.), Columbia University Medical Center, New York, New York
| | - Myles H Akabas
- Departments of Physiology and Biophysics (A.A., R.D., Y.S., S.N.N., M.H.A.) and Neuroscience and Medicine (M.H.A.), Albert Einstein College of Medicine, Bronx, New York; and Departments Microbiology and Immunology (P.P.H., T.R.S.K., D.A.F.) and Medicine (D.A.F.), Columbia University Medical Center, New York, New York
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10
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Targeting the Plasmodium vivax equilibrative nucleoside transporter 1 (PvENT1) for antimalarial drug development. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2015; 6:1-11. [PMID: 26862473 PMCID: PMC4706624 DOI: 10.1016/j.ijpddr.2015.11.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Revised: 11/18/2015] [Accepted: 11/25/2015] [Indexed: 11/26/2022]
Abstract
Infection with Plasmodium falciparum and vivax cause most cases of malaria. Emerging resistance to current antimalarial medications makes new drug development imperative. Ideally a new antimalarial drug should treat both falciparum and vivax malaria. Because malaria parasites are purine auxotrophic, they rely on purines imported from the host erythrocyte via Equilibrative Nucleoside Transporters (ENTs). Thus, the purine import transporters represent a potential target for antimalarial drug development. For falciparum parasites the primary purine transporter is the P. falciparum Equilibrative Nucleoside Transporter Type 1 (PfENT1). Recently we identified potent PfENT1 inhibitors with nanomolar IC50 values using a robust, yeast-based high throughput screening assay. In the current work we characterized the Plasmodium vivax ENT1 (PvENT1) homologue and its sensitivity to the PfENT1 inhibitors. We expressed a yeast codon-optimized PvENT1 gene in Saccharomyces cerevisiae. PvENT1-expressing yeast imported both purines ([3H]adenosine) and pyrimidines ([3H]uridine), whereas wild type (fui1Δ) yeast did not. Based on radiolabel substrate uptake inhibition experiments, inosine had the lowest IC50 (3.8 μM), compared to guanosine (14.9 μM) and adenosine (142 μM). For pyrimidines, thymidine had an IC50 of 183 μM (vs. cytidine and uridine; mM range). IC50 values were higher for nucleobases compared to the corresponding nucleosides; hypoxanthine had a 25-fold higher IC50 than inosine. The archetypal human ENT1 inhibitor 4-nitrobenzylthioinosine (NBMPR) had no effect on PvENT1, whereas dipyridamole inhibited PvENT1, albeit with a 40 μM IC50, a 1000-fold less sensitive than human ENT1 (hENT1). The PfENT1 inhibitors blocked transport activity of PvENT1 and the five known naturally occurring non-synonymous single nucleotide polymorphisms (SNPs) with similar IC50 values. Thus, the PfENT1 inhibitors also target PvENT1. This implies that development of novel antimalarial drugs that target both falciparum and vivax ENT1 may be feasible. PvENT1 can be functionally expressed in Saccharomyces cerevisiae. PvENT1 transports purine and pyrimidine nucleosides and nucleobases but does not transport nucleotides. PvENT1 is inhibited by recently described PfENT1 inhibitors with similar potency. Identified PvENT1 non-synonymous SNPs do not change PfENT1 inhibitor potency. Plasmodium ENTs may be feasible target for development of novel antimalarial drugs.
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Key Words
- ACT, Artemisinin-based Combination Therapies
- CQ, chloroquine
- Drug development
- EC50, concentration causing 50% of maximal effect
- ENT, equilibrative nucleoside transporter
- EV, empty vector
- HTS, high throughput screen
- IC50, concentration causing 50% inhibition
- Malaria
- NBMPR, 4-nitrobenzylthioinosine
- Nucleoside/nucleobase transport
- Parasite
- PfENT1, P. falciparum ENT type 1
- Plasmodium vivax
- Purines
- PvENT1, P. vivax ENT type 1
- SDM, synthetic defined media
- SNP, single nucleotide polymorphism
- Single-nucleotide polymorphism (SNP)
- Transporter
- WHO, World Health Organization
- WT, wild type
- hENT1, human ENT type 1
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11
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Spillman NJ, Kirk K. The malaria parasite cation ATPase PfATP4 and its role in the mechanism of action of a new arsenal of antimalarial drugs. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2015; 5:149-62. [PMID: 26401486 PMCID: PMC4559606 DOI: 10.1016/j.ijpddr.2015.07.001] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Revised: 07/03/2015] [Accepted: 07/08/2015] [Indexed: 11/28/2022]
Abstract
The intraerythrocytic malaria parasite, Plasmodium falciparum, maintains a low cytosolic Na(+) concentration and the plasma membrane P-type cation translocating ATPase 'PfATP4' has been implicated as playing a key role in this process. PfATP4 has been the subject of significant attention in recent years as mutations in this protein confer resistance to a growing number of new antimalarial compounds, including the spiroindolones, the pyrazoles, the dihydroisoquinolones, and a number of the antimalarial agents in the Medicines for Malaria Venture's 'Malaria Box'. On exposure of parasites to these compounds there is a rapid disruption of cytosolic Na(+). Whether, and if so how, such chemically distinct compounds interact with PfATP4, and how such interactions lead to parasite death, is not yet clear. The fact that multiple different chemical classes have converged upon PfATP4 highlights its significance as a potential target for new generation antimalarial agents. A spiroindolone (KAE609, now known as cipargamin) has progressed through Phase I and IIa clinical trials with favourable results. In this review we consider the physiological role of PfATP4, summarise the current repertoire of antimalarial compounds for which PfATP4 is implicated in their mechanism of action, and provide an outlook on translation from target identification in the laboratory to patient treatment in the field.
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Affiliation(s)
- Natalie Jane Spillman
- Research School of Biology, The Australian National University, Canberra, Australian Capital Territory 2601, Australia ; Department of Medicine (Infectious Diseases), Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Kiaran Kirk
- Research School of Biology, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
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12
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Srivastava A, Creek DJ, Evans KJ, De Souza D, Schofield L, Müller S, Barrett MP, McConville MJ, Waters AP. Host reticulocytes provide metabolic reservoirs that can be exploited by malaria parasites. PLoS Pathog 2015; 11:e1004882. [PMID: 26042734 PMCID: PMC4456406 DOI: 10.1371/journal.ppat.1004882] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Accepted: 04/14/2015] [Indexed: 11/18/2022] Open
Abstract
Human malaria parasites proliferate in different erythroid cell types during infection. Whilst Plasmodium vivax exhibits a strong preference for immature reticulocytes, the more pathogenic P. falciparum primarily infects mature erythrocytes. In order to assess if these two cell types offer different growth conditions and relate them to parasite preference, we compared the metabolomes of human and rodent reticulocytes with those of their mature erythrocyte counterparts. Reticulocytes were found to have a more complex, enriched metabolic profile than mature erythrocytes and a higher level of metabolic overlap between reticulocyte resident parasite stages and their host cell. This redundancy was assessed by generating a panel of mutants of the rodent malaria parasite P. berghei with defects in intermediary carbon metabolism (ICM) and pyrimidine biosynthesis known to be important for P. falciparum growth and survival in vitro in mature erythrocytes. P. berghei ICM mutants (pbpepc-, phosphoenolpyruvate carboxylase and pbmdh-, malate dehydrogenase) multiplied in reticulocytes and committed to sexual development like wild type parasites. However, P. berghei pyrimidine biosynthesis mutants (pboprt-, orotate phosphoribosyltransferase and pbompdc-, orotidine 5'-monophosphate decarboxylase) were restricted to growth in the youngest forms of reticulocytes and had a severe slow growth phenotype in part resulting from reduced merozoite production. The pbpepc-, pboprt- and pbompdc- mutants retained virulence in mice implying that malaria parasites can partially salvage pyrimidines but failed to complete differentiation to various stages in mosquitoes. These findings suggest that species-specific differences in Plasmodium host cell tropism result in marked differences in the necessity for parasite intrinsic metabolism. These data have implications for drug design when targeting mature erythrocyte or reticulocyte resident parasites.
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Affiliation(s)
- Anubhav Srivastava
- Wellcome Trust Centre for Molecular Parasitology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
- Institute of Infection, Immunity & Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
| | - Darren J. Creek
- Wellcome Trust Centre for Molecular Parasitology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
- Institute of Infection, Immunity & Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Australia
| | - Krystal J. Evans
- Walter and Eliza Hall Institute of Medical Research, Division of Infection and Immunity, Parkville, Victoria, Australia
| | - David De Souza
- Metabolomics Australia, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
| | - Louis Schofield
- Walter and Eliza Hall Institute of Medical Research, Division of Infection and Immunity, Parkville, Victoria, Australia
- Australian Institute of Tropical Health and Medicine, Centre for Biodiscovery and Molecular Development of Therapeutics, James Cook University, Townsville, Australia
| | - Sylke Müller
- Institute of Infection, Immunity & Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
| | - Michael P. Barrett
- Wellcome Trust Centre for Molecular Parasitology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
- Institute of Infection, Immunity & Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
| | - Malcolm J. McConville
- Metabolomics Australia, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
- Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia
| | - Andrew P. Waters
- Wellcome Trust Centre for Molecular Parasitology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
- Institute of Infection, Immunity & Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Scotland, United Kingdom
- * E-mail:
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13
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Frame IJ, Deniskin R, Rinderspacher A, Katz F, Deng SX, Moir RD, Adjalley SH, Coburn-Flynn O, Fidock DA, Willis IM, Landry DW, Akabas MH. Yeast-based high-throughput screen identifies Plasmodium falciparum equilibrative nucleoside transporter 1 inhibitors that kill malaria parasites. ACS Chem Biol 2015; 10:775-83. [PMID: 25602169 DOI: 10.1021/cb500981y] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Equilibrative transporters are potential drug targets; however, most functional assays involve radioactive substrate uptake that is unsuitable for high-throughput screens (HTS). We developed a robust yeast-based growth assay that is potentially applicable to many equilibrative transporters. As proof of principle, we applied our approach to Equilibrative Nucleoside Transporter 1 of the malarial parasite Plasmodium falciparum (PfENT1). PfENT1 inhibitors might serve as novel antimalarial drugs since PfENT1-mediated purine import is essential for parasite proliferation. To identify PfENT1 inhibitors, we screened 64 560 compounds and identified 171 by their ability to rescue the growth of PfENT1-expressing fui1Δ yeast in the presence of a cytotoxic PfENT1 substrate, 5-fluorouridine (5-FUrd). In secondary assays, nine of the highest activity compounds inhibited PfENT1-dependent growth of a purine auxotrophic yeast strain with adenosine as the sole purine source (IC50 0.2-2 μM). These nine compounds completely blocked [(3)H]adenosine uptake into PfENT1-expressing yeast and erythrocyte-free trophozoite-stage parasites (IC50 5-50 nM), and inhibited chloroquine-sensitive and -resistant parasite proliferation (IC50 5-50 μM). Wild-type (WT) parasite IC50 values were up to 4-fold lower compared to PfENT1-knockout (pfent1Δ) parasites. pfent1Δ parasite killing showed a delayed-death phenotype not observed with WT. We infer that, in parasites, the compounds inhibit both PfENT1 and a secondary target with similar efficacy. The secondary target identity is unknown, but its existence may reduce the likelihood of parasites developing resistance to PfENT1 inhibitors. Our data support the hypothesis that blocking purine transport through PfENT1 may be a novel and compelling approach for antimalarial drug development.
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Affiliation(s)
- I. J. Frame
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Roman Deniskin
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Alison Rinderspacher
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Francine Katz
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Shi-Xian Deng
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Robyn D. Moir
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Sophie H. Adjalley
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Olivia Coburn-Flynn
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - David A. Fidock
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Ian M. Willis
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Donald W. Landry
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Myles H. Akabas
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
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14
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Frame IJ, Deniskin R, Arora A, Akabas MH. Purine import into malaria parasites as a target for antimalarial drug development. Ann N Y Acad Sci 2014; 1342:19-28. [PMID: 25424653 DOI: 10.1111/nyas.12568] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Infection with Plasmodium species parasites causes malaria. Plasmodium parasites are purine auxotrophs. In all life cycle stages, they require purines for RNA and DNA synthesis and other cellular metabolic processes. Purines are imported from the host erythrocyte by equilibrative nucleoside transporters (ENTs). They are processed via purine salvage pathway enzymes to form the required purine nucleotides. The Plasmodium falciparum genome encodes four putative ENTs (PfENT1-4). Genetic, biochemical, and physiologic evidence suggest that PfENT1 is the primary purine transporter supplying the purine salvage pathway. Protein mass spectrometry shows that PfENT1 is expressed in all parasite stages. PfENT1 knockout parasites are not viable in culture at purine concentrations found in human blood (<10 μM). Thus, PfENT1 is a potential target for novel antimalarial drugs, but no PfENT1 inhibitors have been identified to test the hypothesis. Identifying inhibitors of PfENT1 is an essential step to validate PfENT1 as a potential antimalarial drug target.
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Affiliation(s)
- I J Frame
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York
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15
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le Roux D, Burger PB, Niemand J, Grobler A, Urbán P, Fernàndez-Busquets X, Barker RH, Serrano AE, I Louw A, Birkholtz LM. Novel S-adenosyl-L-methionine decarboxylase inhibitors as potent antiproliferative agents against intraerythrocytic Plasmodium falciparum parasites. INTERNATIONAL JOURNAL FOR PARASITOLOGY-DRUGS AND DRUG RESISTANCE 2013; 4:28-36. [PMID: 24596666 PMCID: PMC3940083 DOI: 10.1016/j.ijpddr.2013.11.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 11/19/2013] [Accepted: 11/20/2013] [Indexed: 12/31/2022]
Abstract
S-adenosyl-l-methionine decarboxylase (AdoMetDC) in the polyamine biosynthesis pathway has been identified as a suitable drug target in Plasmodium falciparum parasites, which causes the most lethal form of malaria. Derivatives of an irreversible inhibitor of this enzyme, 5'-{[(Z)-4-amino-2-butenyl]methylamino}-5'-deoxyadenosine (MDL73811), have been developed with improved pharmacokinetic profiles and activity against related parasites, Trypanosoma brucei. Here, these derivatives were assayed for inhibition of AdoMetDC from P. falciparum parasites and the methylated derivative, 8-methyl-5'-{[(Z)-4-aminobut-2-enyl]methylamino}-5'-deoxyadenosine (Genz-644131) was shown to be the most active. The in vitro efficacy of Genz-644131 was markedly increased by nanoencapsulation in immunoliposomes, which specifically targeted intraerythrocytic P. falciparum parasites.
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Affiliation(s)
- Dina le Roux
- Department of Biochemistry, Centre for Sustainable Malaria Control, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| | - Pieter B Burger
- Department of Biochemistry, Centre for Sustainable Malaria Control, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| | - Jandeli Niemand
- Department of Biochemistry, Centre for Sustainable Malaria Control, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| | - Anne Grobler
- DST/NWU Preclinical Drug Development Platform, North-West University, Potchefstroom 2531, South Africa
| | - Patricia Urbán
- Nanobioengineering Group, Institute for Bioengineering of Catalonia, Baldiri Reixac 10-12, Barcelona E08028, Spain ; Barcelona Centre for International Health Research (CRESIB), Hospital Clínic-Universitat de Barcelona, Rosselló 149-153, Barcelona E08036, Spain ; Biomolecular Interactions Team, Nanoscience and Nanotechnology Institute (IN2UB), University of Barcelona, Martí i Franquès 1, Barcelona E08028, Spain
| | - Xavier Fernàndez-Busquets
- Nanobioengineering Group, Institute for Bioengineering of Catalonia, Baldiri Reixac 10-12, Barcelona E08028, Spain ; Barcelona Centre for International Health Research (CRESIB), Hospital Clínic-Universitat de Barcelona, Rosselló 149-153, Barcelona E08036, Spain ; Biomolecular Interactions Team, Nanoscience and Nanotechnology Institute (IN2UB), University of Barcelona, Martí i Franquès 1, Barcelona E08028, Spain
| | - Robert H Barker
- Genzyme Corporation, 153 Second Avenue, Waltham, MA 02451, USA
| | - Adelfa E Serrano
- University of Puerto Rico-School of Medicine, Department of Microbiology and Medical Zoology, P.O. Box 365067, San Juan PR 00936-5067, Puerto Rico
| | - Abraham I Louw
- Department of Biochemistry, Centre for Sustainable Malaria Control, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| | - Lyn-Marie Birkholtz
- Department of Biochemistry, Centre for Sustainable Malaria Control, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
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16
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Brunner R, Ng CL, Aissaoui H, Akabas MH, Boss C, Brun R, Callaghan PS, Corminboeuf O, Fidock DA, Frame IJ, Heidmann B, Le Bihan A, Jenö P, Mattheis C, Moes S, Müller IB, Paguio M, Roepe PD, Siegrist R, Voss T, Welford RWD, Wittlin S, Binkert C. UV-triggered affinity capture identifies interactions between the Plasmodium falciparum multidrug resistance protein 1 (PfMDR1) and antimalarial agents in live parasitized cells. J Biol Chem 2013; 288:22576-83. [PMID: 23754276 DOI: 10.1074/jbc.m113.453159] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
A representative of a new class of potent antimalarials with an unknown mode of action was recently described. To identify the molecular target of this class of antimalarials, we employed a photo-reactive affinity capture method to find parasite proteins specifically interacting with the capture compound in living parasitized cells. The capture reagent retained the antimalarial properties of the parent molecule (ACT-213615) and accumulated within parasites. We identified several proteins interacting with the capture compound and established a functional interaction between ACT-213615 and PfMDR1. We surmise that PfMDR1 may play a role in the antimalarial activity of the piperazine-containing compound ACT-213615.
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Affiliation(s)
- Ralf Brunner
- Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, CH-4002 Basel, Switzerland
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17
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Experimental cerebral malaria is suppressed by disruption of nucleoside transporter 1 but not purine nucleoside phosphorylase. Biochem Biophys Res Commun 2013; 432:504-8. [DOI: 10.1016/j.bbrc.2013.02.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Accepted: 02/03/2013] [Indexed: 11/23/2022]
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18
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Malaria parasite type 4 equilibrative nucleoside transporters (ENT4) are purine transporters with distinct substrate specificity. Biochem J 2012; 446:179-90. [PMID: 22670848 DOI: 10.1042/bj20112220] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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 μM dipyridamole. 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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Cruz LN, Juliano MA, Budu A, Juliano L, Holder AA, Blackman MJ, Garcia CR. Extracellular ATP triggers proteolysis and cytosolic Ca²⁺ rise in Plasmodium berghei and Plasmodium yoelii malaria parasites. Malar J 2012; 11:69. [PMID: 22420332 PMCID: PMC3358241 DOI: 10.1186/1475-2875-11-69] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 03/15/2012] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND Plasmodium has a complex cell biology and it is essential to dissect the cell-signalling pathways underlying its survival within the host. METHODS Using the fluorescence resonance energy transfer (FRET) peptide substrate Abz-AIKFFARQ-EDDnp and Fluo4/AM, the effects of extracellular ATP on triggering proteolysis and Ca²⁺ signalling in Plasmodium berghei and Plasmodium yoelii malaria parasites were investigated. RESULTS The protease activity was blocked in the presence of the purinergic receptor blockers suramin (50 μM) and PPADS (50 μM) or the extracellular and intracellular calcium chelators EGTA (5 mM) and BAPTA/AM (25, 100, 200 and 500 μM), respectively for P. yoelii and P. berghei. Addition of ATP (50, 70, 200 and 250 μM) to isolated parasites previously loaded with Fluo4/AM in a Ca²⁺-containing medium led to an increase in cytosolic calcium. This rise was blocked by pre-incubating the parasites with either purinergic antagonists PPADS (50 μM), TNP-ATP (50 μM) or the purinergic blockers KN-62 (10 μM) and Ip5I (10 μM). Incubating P. berghei infected cells with KN-62 (200 μM) resulted in a changed profile of merozoite surface protein 1 (MSP1) processing as revealed by western blot assays. Moreover incubating P. berghei for 17 h with KN-62 (10 μM) led to an increase in rings forms (82% ± 4, n = 11) and a decrease in trophozoite forms (18% ± 4, n = 11). CONCLUSIONS The data clearly show that purinergic signalling modulates P. berghei protease(s) activity and that MSP1 is one target in this pathway.
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Affiliation(s)
- Laura Nogueira Cruz
- Department of Physiology, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, Butantan, 05508-900 São Paulo, SP Brazil
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Yao SYM, Ng AML, Cass CE, Baldwin SA, Young JD. Nucleobase transport by human equilibrative nucleoside transporter 1 (hENT1). J Biol Chem 2011; 286:32552-62. [PMID: 21795683 DOI: 10.1074/jbc.m111.236117] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The human equilibrative nucleoside transporters hENT1 and hENT2 (each with 456 residues) are 40% identical in amino acid sequence and contain 11 putative transmembrane helices. Both transport purine and pyrimidine nucleosides and are distinguished functionally by a difference in sensitivity to inhibition by nanomolar concentrations of nitrobenzylmercaptopurine ribonucleoside (NBMPR), hENT1 being NBMPR-sensitive. Previously, we used heterologous expression in Xenopus oocytes to demonstrate that recombinant hENT2 and its rat ortholog rENT2 also transport purine and pyrimidine bases, h/rENT2 representing the first identified mammalian nucleobase transporter proteins (Yao, S. Y., Ng, A. M., Vickers, M. F., Sundaram, M., Cass, C. E., Baldwin, S. A., and Young, J. D. (2002) J. Biol. Chem. 277, 24938-24948). The same study also revealed lower, but significant, transport of hypoxanthine by h/rENT1. In the present investigation, we have used the enhanced Xenopus oocyte expression vector pGEMHE to demonstrate that hENT1 additionally transports thymine and adenine and, to a lesser extent, uracil and guanine. Fluxes of hypoxanthine, thymine, and adenine by hENT1 were saturable and inhibited by NBMPR. Ratios of V(max) (pmol/oocyte · min(-1)):K(m) (mm), a measure of transport efficiency, were 86, 177, and 120 for hypoxantine, thymine, and adenine, respectively, compared with 265 for uridine. Hypoxanthine influx was competitively inhibited by uridine, indicating common or overlapping nucleobase and nucleoside permeant binding pockets, and the anticancer nucleobase drugs 5-fluorouracil and 6-mercaptopurine were also transported. Nucleobase transport activity was absent from an engineered cysteine-less version hENT1 (hENT1C-) in which all 10 endogenous cysteine residues were mutated to serine. Site-directed mutagenesis identified Cys-414 in transmembrane helix 10 of hENT1 as the residue conferring nucleobase transport activity to the wild-type transporter.
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Affiliation(s)
- Sylvia Y M Yao
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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21
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Nutrient transport and pathogenesis in selected parasitic protozoa. EUKARYOTIC CELL 2011; 10:483-93. [PMID: 21216940 DOI: 10.1128/ec.00287-10] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Parasitic protozoa, such as malaria parasites, trypanosomes, and Leishmania, acquire a plethora of nutrients from their hosts, employing transport proteins located in the plasma membrane of the parasite. Application of molecular genetic approaches and the completion of genome projects have allowed the identification and functional characterization of a cohort of transporters and their genes in these parasites. This review focuses on a subset of these permeases that have been studied in some detail, that import critical nutrients, and that provide examples of approaches being undertaken broadly with these and other parasite transporters. Permeases reviewed include those for hexoses, purines, iron, polyamines, carboxylates, and amino acids. Topics of special emphasis include structure-function approaches, critical roles for transporters in parasite viability and physiology, regulation of transporter expression, and subcellular targeting. Investigations of parasite transporters impact a broad spectrum of basic biological problems in these protozoa.
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Huthmacher C, Hoppe A, Bulik S, Holzhütter HG. Antimalarial drug targets in Plasmodium falciparum predicted by stage-specific metabolic network analysis. BMC SYSTEMS BIOLOGY 2010; 4:120. [PMID: 20807400 PMCID: PMC2941759 DOI: 10.1186/1752-0509-4-120] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Accepted: 08/31/2010] [Indexed: 12/20/2022]
Abstract
BACKGROUND Despite enormous efforts to combat malaria the disease still afflicts up to half a billion people each year of which more than one million die. Currently no approved vaccine is available and resistances to antimalarials are widely spread. Hence, new antimalarial drugs are urgently needed. RESULTS Here, we present a computational analysis of the metabolism of Plasmodium falciparum, the deadliest malaria pathogen. We assembled a compartmentalized metabolic model and predicted life cycle stage specific metabolism with the help of a flux balance approach that integrates gene expression data. Predicted metabolite exchanges between parasite and host were found to be in good accordance with experimental findings when the parasite's metabolic network was embedded into that of its host (erythrocyte). Knock-out simulations identified 307 indispensable metabolic reactions within the parasite. 35 out of 57 experimentally demonstrated essential enzymes were recovered and another 16 enzymes, if additionally the assumption was made that nutrient uptake from the host cell is limited and all reactions catalyzed by the inhibited enzyme are blocked. This predicted set of putative drug targets, shown to be enriched with true targets by a factor of at least 2.75, was further analyzed with respect to homology to human enzymes, functional similarity to therapeutic targets in other organisms and their predicted potency for prophylaxis and disease treatment. CONCLUSIONS The results suggest that the set of essential enzymes predicted by our flux balance approach represents a promising starting point for further drug development.
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Affiliation(s)
- Carola Huthmacher
- Institute of Biochemistry, Charité, Monbijoustraße 2, 10117 Berlin, Germany
| | - Andreas Hoppe
- Institute of Biochemistry, Charité, Monbijoustraße 2, 10117 Berlin, Germany
| | - Sascha Bulik
- Institute of Biochemistry, Charité, Monbijoustraße 2, 10117 Berlin, Germany
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Keough DT, Hocková D, Krecmerová M, Cesnek M, Holý A, Naesens L, Brereton IM, Winzor DJ, de Jersey J, Guddat LW. Plasmodium vivax hypoxanthine-guanine phosphoribosyltransferase: a target for anti-malarial chemotherapy. Mol Biochem Parasitol 2010; 173:165-9. [PMID: 20595032 DOI: 10.1016/j.molbiopara.2010.05.018] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 05/25/2010] [Accepted: 05/25/2010] [Indexed: 11/30/2022]
Abstract
The malarial parasite, Plasmodium vivax (Pv), causes a serious infectious disease found primarily in Asia and the Americas. For protozoan parasites, 6-oxopurine phosphoribosyltransferases (PRTases) provide the only metabolic pathway to synthesize the purine nucleoside monophosphates essential for DNA/RNA production. We have purified the recombinant Pv 6-oxopurine (PRTase) and compared its properties with the human and Pf enzymes. The Pv enzyme uses hypoxanthine and guanine with similar catalytic efficiency to the Pf enzyme but xanthine is not a substrate, hence we identify this enzyme as PvHGPRT. Mass spectrometry suggests that PvHGPRT contains bound magnesium ions that are removed by EDTA resulting in loss of activity. However, the addition of Mg(2+) restores activity. Acyclic nucleoside phosphonates (ANPs) are good inhibitors of PvHGPRT having K(i) values as low as 3 microM. These compounds can form the basis for the design of new drugs aimed at combating malaria caused by Pv.
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Affiliation(s)
- Dianne T Keough
- The School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, 4072, QLD, Australia
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24
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Exploiting the therapeutic potential of Plasmodium falciparum solute transporters. Trends Parasitol 2010; 26:284-96. [DOI: 10.1016/j.pt.2010.03.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2009] [Revised: 03/02/2010] [Accepted: 03/05/2010] [Indexed: 01/16/2023]
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25
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Downie MJ, El Bissati K, Bobenchik AM, Nic Lochlainn L, Amerik A, Zufferey R, Kirk K, Ben Mamoun C. PfNT2, a permease of the equilibrative nucleoside transporter family in the endoplasmic reticulum of Plasmodium falciparum. J Biol Chem 2010; 285:20827-33. [PMID: 20439460 DOI: 10.1074/jbc.m110.118489] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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.
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Affiliation(s)
- Megan J Downie
- Section of Infectious Diseases, Yale School of Medicine, New Haven, CT 06512, USA
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26
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Riegelhaupt PM, Frame IJ, Akabas MH. Transmembrane segment 11 appears to line the purine permeation pathway of the Plasmodium falciparum equilibrative nucleoside transporter 1 (PfENT1). J Biol Chem 2010; 285:17001-10. [PMID: 20335165 DOI: 10.1074/jbc.m110.115758] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Purine transport is essential for malaria parasites to grow because they lack the enzymes necessary for de novo purine biosynthesis. The Plasmodium falciparum Equilibrative Nucleoside Transporter 1 (PfENT1) is a member of the equilibrative nucleoside transporter (ENT) gene family. PfENT1 is a primary purine transport pathway across the P. falciparum plasma membrane because PfENT1 knock-out parasites are not viable at physiologic extracellular purine concentrations. Topology predictions and experimental data indicate that ENT family members have eleven transmembrane (TM) segments although their tertiary structure is unknown. In the current work, we showed that a naturally occurring polymorphism, F394L, in TM11 affects transport substrate K(m). We investigated the structure and function of the TM11 segment using the substituted cysteine accessibility method. We showed that mutation to Cys of two highly conserved glycine residues in a GXXXG motif significantly reduces PfENT1 protein expression levels. We speculate that the conserved TM11 GXXXG glycines may be critical for folding and/or assembly. Small, cysteine-specific methanethiosulfonate (MTS) reagents reacted with four TM11 Cys substitution mutants, L393C, I397C, T400C, and Y403C. Larger MTS reagents do not react with the more cytoplasmic positions. Hypoxanthine, a transported substrate, protected L393C, I397C, and T400C from covalent modification by the MTS reagents. Plotted on an alpha-helical wheel, Leu-393, Ile-397, and Thr-400 lie on one face of the helix in a 60 degrees arc suggesting that TM11 is largely alpha helical. We infer that they line a water-accessible surface, possibly the purine permeation pathway. These results advance our understanding of the ENT structure.
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Affiliation(s)
- Paul M Riegelhaupt
- Department of Physiology and Biophysics, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA
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27
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Quashie NB, Ranford-Cartwright LC, de Koning HP. Uptake of purines in Plasmodium falciparum-infected human erythrocytes is mostly mediated by the human equilibrative nucleoside transporter and the human facilitative nucleobase transporter. Malar J 2010; 9:36. [PMID: 20113503 PMCID: PMC2825241 DOI: 10.1186/1475-2875-9-36] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Accepted: 01/29/2010] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND Plasmodium parasites are unable to synthesize purines de novo and have to salvage them from the host. Due to this limitation in the parasite, purine transporters have been an area of focus in the search for anti-malarial drugs. Although the uptake of purines through the human equilibrative nucleoside transporter (hENT1), the human facilitative nucleobase transporter (hFNT1) and the parasite-induced new permeation pathway (NPP) has been studied, no information appears to exist on the relative contribution of these three transporters to the uptake of adenosine and hypoxanthine. Using the appropriate transporter inhibitors, the role of each of these salvage pathways to the overall purine transport in intraerythrocytic Plasmodium falciparum was systematically investigated. METHODS The transport of adenosine, hypoxanthine and adenine into uninfected and P. falciparum-infected human erythrocytes was investigated in the presence or absence of classical inhibitors of the hFNT1, hENT1 and NPP. The effective inhibition of the various transporters by the classical inhibitors was verified using appropriate known substrates. The ability of high concentration of unlabelled substrates to saturate these transporters was also studied. RESULTS Transport of exogenous purine into infected or uninfected erythrocytes occurred primarily through saturable transporters rather than through the NPP. Hypoxanthine and adenine appeared to enter erythrocytes mainly through the hFNT1 nucleobase transporter whereas adenosine entered predominantly through the hENT1 nucleoside transporter. The rate of purine uptake was approximately doubled in infected cells compared to uninfected erythrocytes. In addition, it was found that the rate of adenosine uptake was considerably higher than the rate of hypoxanthine uptake in infected human red blood cells (RBC). It was also demonstrated that furosemide inhibited the transport of purine bases through hFNT1. CONCLUSION Collectively, the data obtained in this study clearly show that the endogenous host erythrocyte transporters hENT1 and hFNT1, rather than the NPP, are the major route of entry of purine into parasitized RBC. Inhibitors of hENT1 and hFNT1, as well as the NPP, should be considered in the development of anti-malarials targeted to purine transport.
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Affiliation(s)
- Neils B Quashie
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow G12 8TA, UK
- Centre for Tropical Clinical Pharmacology and Therapeutics, University of Ghana Medical School, PO Box GP 4236, Accra Ghana
| | - Lisa C Ranford-Cartwright
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow G12 8TA, UK
| | - Harry P de Koning
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow G12 8TA, UK
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Riegelhaupt PM, Cassera MB, Fröhlich RFG, Hazleton KZ, Hefter JJ, Schramm VL, Akabas MH. Transport of purines and purine salvage pathway inhibitors by the Plasmodium falciparum equilibrative nucleoside transporter PfENT1. Mol Biochem Parasitol 2009; 169:40-9. [PMID: 19818813 DOI: 10.1016/j.molbiopara.2009.10.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Revised: 09/24/2009] [Accepted: 10/04/2009] [Indexed: 11/28/2022]
Abstract
Plasmodium falciparum is a purine auxotroph. The transport of purine nucleosides and nucleobases from the host erythrocyte to the parasite cytoplasm is essential to support parasite growth. P. falciparum equilibrative nucleoside transporter 1 (PfENT1) is a major route for purine transport across the parasite plasma membrane. Malarial parasites are sensitive to inhibitors of purine salvage pathway enzymes. The immucillin class of purine nucleoside phosphorylase inhibitors and the adenosine analog, tubercidin, block growth of P. falciparum under in vitro culture conditions. We sought to determine whether these inhibitors utilize PfENT1 to gain access to the parasite cytosol. There is considerable controversy in the literature regarding the K(m) and/or K(i) for purine transport by PfENT1 in the Xenopus oocyte expression system. We show that oocytes metabolize adenosine but not hypoxanthine. For adenosine, metabolism is the rate limiting step in oocyte uptake assays, making hypoxanthine the preferred substrate for PfENT1 transport studies in oocytes. We demonstrate that the K(i) for PfENT1 transport of hypoxanthine and adenosine is in the 300-700microM range. Effects of substrate metabolism on uptake studies may explain conflicting results in the literature regarding the PfENT1 adenosine transport K(m). PfENT1 transports the tubercidin class of compounds. None of the immucillin compounds tested inhibited PfENT1 transport of [(3)H]hypoxanthine or [(3)H]adenosine. Although nucleobases are transported, modifications of the ribose ring in corresponding nucleoside analogs affect substrate recognition by PfENT1. These results provide new insights into PfENT1 and the mechanism by which purine salvage pathway inhibitors are transported into the parasite cytoplasm.
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Affiliation(s)
- Paul M Riegelhaupt
- Department of Physiology and Biophysics, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY 10461, USA
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29
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Kirk K, Howitt SM, Bröer S, Saliba KJ, Downie MJ. Purine uptake in Plasmodium: transport versus metabolism. Trends Parasitol 2009; 25:246-9. [PMID: 19423394 DOI: 10.1016/j.pt.2009.03.006] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2008] [Revised: 08/28/2008] [Accepted: 03/13/2009] [Indexed: 10/20/2022]
Abstract
In a recent paper, Quashie et al. have proposed that purine uptake into the intraerythrocytic malaria parasite involves four different plasma membrane transporters - two high affinity and two low affinity. They equate one of the two high-affinity transporters with PfNT1, a transporter reported previously to be a low-affinity system. Here, we offer an alternative interpretation of their data, suggesting that the conclusions drawn by Quashie et al. take insufficient account of metabolism.
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Affiliation(s)
- Kiaran Kirk
- Biochemistry and Molecular Biology, School of Biology, The Australian National University, Canberra ACT 0200, Australia.
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30
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Madrid DC, Ting LM, Waller KL, Schramm VL, Kim K. Plasmodium falciparum purine nucleoside phosphorylase is critical for viability of malaria parasites. J Biol Chem 2008; 283:35899-907. [PMID: 18957439 PMCID: PMC2602904 DOI: 10.1074/jbc.m807218200] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2008] [Revised: 10/22/2008] [Indexed: 11/06/2022] Open
Abstract
Human malaria infections resulting from Plasmodium falciparum have become increasingly difficult to treat due to the emergence of drug-resistant parasites. The P. falciparum purine salvage enzyme purine nucleoside phosphorylase (PfPNP) is a potential drug target. Previous studies, in which PfPNP was targeted by transition state analogue inhibitors, found that those inhibiting human PNP and PfPNPs killed P. falciparum in vitro. However, many drugs have off-target interactions, and genetic evidence is required to demonstrate single target action for this class of potential drugs. We used targeted gene disruption in P. falciparum strain 3D7 to ablate PNP expression, yielding transgenic 3D7 parasites (Deltapfpnp). Lysates of the Deltapfpnp parasites showed no PNP activity, but activity of another purine salvage enzyme, adenosine deaminase (PfADA), was normal. When compared with wild-type 3D7, the Deltapfpnp parasites showed a greater requirement for exogenous purines and a severe growth defect at physiological concentrations of hypoxanthine. Drug assays using immucillins, specific transition state inhibitors of PNP, were performed on wild-type and Deltapfpnp parasites. The Deltapfpnp parasites were more sensitive to PNP inhibitors that bound hPNP tighter and less sensitive to MT-ImmH, an inhibitor with 100-fold preference for PfPNP over hPNP. The results demonstrate the importance of purine salvage in P. falciparum and validate PfPNP as the target of immucillins.
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Affiliation(s)
- Dennis C Madrid
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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31
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Heterologous expression of plasmodial proteins for structural studies and functional annotation. Malar J 2008; 7:197. [PMID: 18828893 PMCID: PMC2567985 DOI: 10.1186/1475-2875-7-197] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2008] [Accepted: 10/01/2008] [Indexed: 11/10/2022] Open
Abstract
Malaria remains the world's most devastating tropical infectious disease with as many as 40% of the world population living in risk areas. The widespread resistance of Plasmodium parasites to the cost-effective chloroquine and antifolates has forced the introduction of more costly drug combinations, such as Coartem®. In the absence of a vaccine in the foreseeable future, one strategy to address the growing malaria problem is to identify and characterize new and durable antimalarial drug targets, the majority of which are parasite proteins. Biochemical and structure-activity analysis of these proteins is ultimately essential in the characterization of such targets but requires large amounts of functional protein. Even though heterologous protein production has now become a relatively routine endeavour for most proteins of diverse origins, the functional expression of soluble plasmodial proteins is highly problematic and slows the progress of antimalarial drug target discovery. Here the status quo of heterologous production of plasmodial proteins is presented, constraints are highlighted and alternative strategies and hosts for functional expression and annotation of plasmodial proteins are reviewed.
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32
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Cassera MB, Hazleton KZ, Riegelhaupt PM, Merino EF, Luo M, Akabas MH, Schramm VL. Erythrocytic adenosine monophosphate as an alternative purine source in Plasmodium falciparum. J Biol Chem 2008; 283:32889-99. [PMID: 18799466 DOI: 10.1074/jbc.m804497200] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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.
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Affiliation(s)
- María B Cassera
- Department of Biochemistry, Albert Einstein College of Medicine, Yeshiva University, Bronx, New York 10461, USA
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El Bissati K, Downie MJ, Kim SK, Horowitz M, Carter N, Ullman B, Ben Mamoun C. Genetic evidence for the essential role of PfNT1 in the transport and utilization of xanthine, guanine, guanosine and adenine by Plasmodium falciparum. Mol Biochem Parasitol 2008; 161:130-9. [PMID: 18639591 DOI: 10.1016/j.molbiopara.2008.06.012] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 06/18/2008] [Accepted: 06/19/2008] [Indexed: 11/16/2022]
Abstract
The malaria parasite, Plasmodium falciparum, is unable to synthesize the purine ring de novo and is therefore wholly dependent upon purine salvage from the host for survival. Previous studies have indicated that a P. falciparum strain in which the purine transporter PfNT1 had been disrupted was unable to grow on physiological concentrations of adenosine, inosine and hypoxanthine. We have now used an episomally complemented pfnt1Delta knockout parasite strain to confirm genetically the functional role of PfNT1 in P. falciparum purine uptake and utilization. Episomal complementation by PfNT1 restored the ability of pfnt1Delta parasites to transport and utilize adenosine, inosine and hypoxanthine as purine sources. The ability of wild-type and pfnt1Delta knockout parasites to transport and utilize the other physiologically relevant purines adenine, guanine, guanosine and xanthine was also examined. Unlike wild-type and complemented P. falciparum parasites, pfnt1Delta parasites could not proliferate on guanine, guanosine or xanthine as purine sources, and no significant transport of these substrates could be detected in isolated parasites. Interestingly, whereas isolated pfnt1Delta parasites were still capable of adenine transport, these parasites grew only when adenine was provided at high, non-physiological concentrations. Taken together these results demonstrate that, in addition to hypoxanthine, inosine and adenosine, PfNT1 is essential for the transport and utilization of xanthine, guanine and guanosine.
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Affiliation(s)
- Kamal El Bissati
- Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030, USA
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Purine salvage pathways in the intraerythrocytic malaria parasite Plasmodium falciparum. EUKARYOTIC CELL 2008; 7:1231-7. [PMID: 18567789 DOI: 10.1128/ec.00159-08] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Critical role of a K+ channel in Plasmodium berghei transmission revealed by targeted gene disruption. Proc Natl Acad Sci U S A 2008; 105:6398-402. [PMID: 18434537 DOI: 10.1073/pnas.0802384105] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Regulated K(+) transport across the plasma membrane is of vital importance for the survival of most cells. Two K(+) channels have been identified in the Plasmodium falciparum genome; however, their functional significance during parasite life cycle in the vertebrate host and during transmission through the mosquito vector remains unknown. We hypothesize that these two K(+) channels mediate the transport of K(+) in the parasites, and thus are important for parasite survival. To test this hypothesis, we identified the orthologue of one of the P. falciparum K(+) channels, PfKch1, in the rodent malaria parasite P. berghei (PbKch1) and examined the biological role by performing a targeted disruption of the gene encoding PbKch1. The deduced amino acid sequence of the six transmembrane domains of PfKch1 and PbKch1 share 82% identity, and in particular the pore regions are completely identical. The PbKch1-null parasites were viable despite a marked reduction in the uptake of the K(+) congener (86)Rb(+), and mice infected with PbKch1-null parasites survived slightly longer than mice infected with WT parasites. However, the most striking feature of the phenotype was the virtually complete inhibition of the development of PbKch1-null parasites in Anopheles stephensi mosquitoes. In conclusion, these studies demonstrate that PbKch1 contributes to the transport of K(+) in P. berghei parasites and supports the growth of the parasites, in particular the development of oocysts in the mosquito midgut. K(+) channels therefore may constitute a potential antimalarial drug target.
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36
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Sherman IW. References. ADVANCES IN PARASITOLOGY 2008. [DOI: 10.1016/s0065-308x(08)00430-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Ghérardi A, Sarciron ME. Molecules targeting the purine salvage pathway in Apicomplexan parasites. Trends Parasitol 2007; 23:384-9. [PMID: 17574921 DOI: 10.1016/j.pt.2007.06.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2006] [Revised: 03/21/2007] [Accepted: 06/06/2007] [Indexed: 01/10/2023]
Abstract
The need of intracellular parasites to retrieve nutrients and fulfill their energy requirements is achieved by manipulating the host's metabolism. With the spread of AIDS, research on purine metabolism has gained in importance with the aim to develop drugs against opportunistic infections. Many studies over the past ten years have yielded contradictory results, but this review tries to clarify these findings by exposing the latest data concerning purine transport and the specific activities of the major enzymes of the purine salvage pathway of Toxoplasma gondii, Plasmodium falciparum and Cryptosporidium parvum.
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Affiliation(s)
- Arnaud Ghérardi
- Pharmaceutical Department of Parasitology and Medical Mycology, Claude-Bernard University Lyon I, 8 Avenue Rockefeller, 69373 Lyon Cedex 08, France
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Too K, Brown DM, Bongard E, Yardley V, Vivas L, Loakes D. Anti-malarial activity of N6-modified purine analogues. Bioorg Med Chem 2007; 15:5551-62. [PMID: 17548196 DOI: 10.1016/j.bmc.2007.05.038] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2007] [Revised: 05/10/2007] [Accepted: 05/15/2007] [Indexed: 11/16/2022]
Abstract
Plasmodium falciparum causes one of the deadliest forms of malaria and resistance to the currently available drugs makes it imperative to develop new, safe and potent drugs. Parasites such as P. falciparum are unable to synthesise purines de novo and to this end often have multiple purine uptake and salvage systems. With this in mind, we have designed and synthesised libraries of purine analogues as potential anti-malarial agents. Herein, we report three compounds with promising activity against the highly chloroquine-resistant VS1 P. falciparum namely: N(6)-hydroxyadenine (1c), 2-amino-N(6)-aminoadenosine (2b) and 2-amino-N(6)-amino-N(6)-methyladenosine (4b).
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Affiliation(s)
- Kathleen Too
- Medical Research Council, Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
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39
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Abstract
Synthesis de novo, acquisition by salvage and interconversion of purines and pyrimidines represent the fundamental requirements for their eventual assembly into nucleic acids as nucleotides and the deployment of their derivatives in other biochemical pathways. A small number of drugs targeted to nucleotide metabolism, by virtue of their effect on folate biosynthesis and recycling, have been successfully used against apicomplexan parasites such as Plasmodium and Toxoplasma for many years, although resistance is now a major problem in the prevention and treatment of malaria. Many targets not involving folate metabolism have also been explored at the experimental level. However, the unravelling of the genome sequences of these eukaryotic unicellular organisms, together with increasingly sophisticated molecular analyses, opens up possibilities of introducing new drugs that could interfere with these processes. This review examines the status of established drugs of this type and the potential for further exploiting the vulnerability of apicomplexan human pathogens to inhibition of this key area of metabolism.
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Affiliation(s)
- John E Hyde
- Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, 131 Princess Street, Manchester M1 7ND, UK.
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Kelly JX, Winter RW, Braun TP, Osei-Agyemang M, Hinrichs DJ, Riscoe MK. Selective killing of the human malaria parasite Plasmodium falciparum by a benzylthiazolium dye. Exp Parasitol 2006; 116:103-10. [PMID: 17266952 PMCID: PMC1965281 DOI: 10.1016/j.exppara.2006.12.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 11/30/2006] [Accepted: 12/06/2006] [Indexed: 11/25/2022]
Abstract
Malaria is an infectious disease caused by protozoan parasites of the genus Plasmodium. The most virulent form of the disease is caused by Plasmodium falciparum which infects hundreds of millions of people and is responsible for the deaths of 1-2 million individuals each year. An essential part of the parasitic process is the remodeling of the red blood cell membrane and its protein constituents to permit a higher flux of nutrients and waste products into or away from the intracellular parasite. Much of this increased permeability is due to a single type of broad specificity channel variously called the new permeation pathway (NPP), the nutrient channel, and the Plasmodial surface anion channel (PSAC). This channel is permeable to a range of low molecular weight solutes both charged and uncharged, with a strong preference for anions. Drugs such as furosemide that are known to block anion-selective channels inhibit PSAC. In this study, we have investigated a dye known as benzothiocarboxypurine, BCP, which had been studied as a possible diagnostic aid given its selective uptake by P. falciparum infected red cells. We found that the dye enters parasitized red cells via the furosemide-inhibitable PSAC, forms a brightly fluorescent complex with parasite nucleic acids, and is selectively toxic to infected cells. Our study describes an antimalarial agent that exploits the altered permeability of Plasmodium-infected red cells as a means to killing the parasite and highlights a chemical reagent that may prove useful in high throughput screening of compounds for inhibitors of the channel.
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Affiliation(s)
- Jane X. Kelly
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
- Department of Chemistry, Portland State University, Portland, Oregon, 97207-0751
| | - Rolf W. Winter
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
- Department of Chemistry, Portland State University, Portland, Oregon, 97207-0751
| | - Theodore P. Braun
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
| | - Myralyn Osei-Agyemang
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
| | - David J. Hinrichs
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
| | - Michael K. Riscoe
- Medical Research Service, RD-33, Department of Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, OR, USA 97239
- Department of Chemistry, Portland State University, Portland, Oregon, 97207-0751
- Mailing Address: *Michael Riscoe, Ph.D., Medical Research Service, RD-33, Veterans Affairs Medical Center, 3710 SW U.S. Veterans Hospital Road, Portland, Oregon 97239 Phone Number: 503-721-7885/Telefacsimile: 503-402-2817/e-mail:
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41
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Downie MJ, Saliba KJ, Howitt SM, Bröer S, Kirk K. Transport of nucleosides across the Plasmodium falciparum parasite plasma membrane has characteristics of PfENT1. Mol Microbiol 2006; 60:738-48. [PMID: 16629674 DOI: 10.1111/j.1365-2958.2006.05125.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Like all parasitic protozoa, the human malaria parasite Plasmodium falciparum lacks the enzymes required for de novo synthesis of purines and it is therefore reliant upon the salvage of these compounds from the external environment. P. falciparum equilibrative nucleoside transporter 1 (PfENT1) is a nucleoside transporter that has been localized to the plasma membrane of the intraerythrocytic form of the parasite. In this study we have characterized the transport of purine and pyrimidine nucleosides across the plasma membrane of 'isolated' trophozoite-stage P. falciparum parasites and compared the transport characteristics of the parasite with those of PfENT1 expressed in Xenopus oocytes. The transport of nucleosides into the parasite: (i) was, in the case of adenosine, inosine and thymidine, very fast, equilibrating within a few seconds; (ii) was of low affinity [K(m) (adenosine) = 1.45 +/- 0.25 mM; K(m) (thymidine) = 1.11 +/- 0.09 mM]; and (iii) showed 'cross-competition' for adenosine, inosine and thymidine, but not cytidine. The kinetic characteristics of nucleoside transport in intact parasites matched very closely those of PfENT1 expressed in Xenopus oocytes [K(m) (adenosine) = 1.86 +/- 0.28 mM; K(m) (thymidine) = 1.33 +/- 0.17 mM]. Furthermore, PfENT1 transported adenosine, inosine and thymidine, with a cross-competition profile the same as that seen for isolated parasites. The data are consistent with PfENT1 serving as a major route for the uptake of nucleosides across the parasite plasma membrane.
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Affiliation(s)
- Megan J Downie
- School of Biochemistry and Molecular Biology, The Australian National University, Canberra ACT 0200, Australia
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El Bissati K, Zufferey R, Witola WH, Carter NS, Ullman B, Ben Mamoun C. The plasma membrane permease PfNT1 is essential for purine salvage in the human malaria parasite Plasmodium falciparum. Proc Natl Acad Sci U S A 2006; 103:9286-91. [PMID: 16751273 PMCID: PMC1482602 DOI: 10.1073/pnas.0602590103] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The human malaria parasite Plasmodium falciparum relies on the acquisition of host purines for its survival within human erythrocytes. Purine salvage by the parasite requires specialized transporters at the parasite plasma membrane (PPM), but the exact mechanism of purine entry into the infected erythrocyte, and the primary purine source used by the parasite, remain unknown. Here, we report that transgenic parasites lacking the PPM transporter PfNT1 (P. falciparum nucleoside transporter 1) are auxotrophic for hypoxanthine, inosine, and adenosine under physiological conditions and are viable only if these normally essential nutrients are provided at excess concentrations. Transport measurements across the PPM revealed a severe reduction in hypoxanthine uptake in the knockout, whereas adenosine and inosine transport were only partially affected. These data provide compelling evidence for a sequential pathway for exogenous purine conversion into hypoxanthine using host enzymes followed by PfNT1-mediated transport into the parasite. The phenotype of the conditionally lethal mutant establishes PfNT1 as a critical component of purine salvage in P. falciparum and validates PfNT1 as a potential therapeutic target.
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Affiliation(s)
- Kamal El Bissati
- *Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030-3301; and
| | - Rachel Zufferey
- *Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030-3301; and
| | - William H. Witola
- *Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030-3301; and
| | - Nicola S. Carter
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, OR 97201
| | - Buddy Ullman
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, OR 97201
| | - Choukri Ben Mamoun
- *Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030-3301; and
- To whom correspondence should be addressed. E-mail:
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Kirk K, Martin RE, Bröer S, Howitt SM, Saliba KJ. Plasmodium permeomics: membrane transport proteins in the malaria parasite. Curr Top Microbiol Immunol 2005; 295:325-56. [PMID: 16265897 DOI: 10.1007/3-540-29088-5_13] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Membrane transport proteins are integral membrane proteins that mediate the passage across the membrane bilayer of specific molecules and/or ions. Such proteins serve a diverse range of physiological roles, mediating the uptake of nutrients into cells, the removal of metabolic wastes and xenobiotics (including drugs), and the generation and maintenance of transmembrane electrochemical gradients. In this chapter we review the present state of knowledge of the membrane transport mechanisms underlying the cell physiology of the intraerythrocytic malaria parasite and its host cell, considering in particular physiological measurements on the parasite and parasitized erythrocyte, the annotation of transport proteins in the Plasmodium genome, and molecular methods used to analyze transport protein function.
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Affiliation(s)
- K Kirk
- School of Biochemistry and Molecular Biology, The Australian National University, 0200 Canberra, ACT, Australia.
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44
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de Koning HP, Bridges DJ, Burchmore RJS. Purine and pyrimidine transport in pathogenic protozoa: From biology to therapy. FEMS Microbiol Rev 2005; 29:987-1020. [PMID: 16040150 DOI: 10.1016/j.femsre.2005.03.004] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2004] [Revised: 03/22/2005] [Accepted: 03/24/2005] [Indexed: 01/10/2023] Open
Abstract
Purine salvage is an essential function for all obligate parasitic protozoa studied to date and most are also capable of efficient uptake of preformed pyrimidines. Much progress has been made in the identification and characterisation of protozoan purine and pyrimidine transporters. While the genes encoding protozoan or metazoan pyrimidine transporters have yet to be identified, numerous purine transporters have now been cloned. All protozoan purine transporter-encoding genes characterised to date have been of the Equilibrative Nucleoside Transporter family conserved in a great variety of eukaryote organisms. However, these protozoan transporters have been shown to be sufficiently different from mammalian transporters to mediate selective uptake of therapeutic agents. Recent studies are increasingly addressing the structure and substrate recognition mechanisms of these vital transport proteins.
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Affiliation(s)
- Harry P de Koning
- Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, UK.
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45
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Martin RE, Henry RI, Abbey JL, Clements JD, Kirk K. The 'permeome' of the malaria parasite: an overview of the membrane transport proteins of Plasmodium falciparum. Genome Biol 2005; 6:R26. [PMID: 15774027 PMCID: PMC1088945 DOI: 10.1186/gb-2005-6-3-r26] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2004] [Revised: 12/31/2004] [Accepted: 01/28/2005] [Indexed: 11/24/2022] Open
Abstract
Bioinformatic and expression analyses attribute putative functions to transporters and channels encoded by the Plasmodium falciparum genome. The malaria parasite has substantially more membrane transport proteins than previously thought. Background The uptake of nutrients, expulsion of metabolic wastes and maintenance of ion homeostasis by the intraerythrocytic malaria parasite is mediated by membrane transport proteins. Proteins of this type are also implicated in the phenomenon of antimalarial drug resistance. However, the initial annotation of the genome of the human malaria parasite Plasmodium falciparum identified only a limited number of transporters, and no channels. In this study we have used a combination of bioinformatic approaches to identify and attribute putative functions to transporters and channels encoded by the malaria parasite, as well as comparing expression patterns for a subset of these. Results A computer program that searches a genome database on the basis of the hydropathy plots of the corresponding proteins was used to identify more than 100 transport proteins encoded by P. falciparum. These include all the transporters previously annotated as such, as well as a similar number of candidate transport proteins that had escaped detection. Detailed sequence analysis enabled the assignment of putative substrate specificities and/or transport mechanisms to all those putative transport proteins previously without. The newly-identified transport proteins include candidate transporters for a range of organic and inorganic nutrients (including sugars, amino acids, nucleosides and vitamins), and several putative ion channels. The stage-dependent expression of RNAs for 34 candidate transport proteins of particular interest are compared. Conclusion The malaria parasite possesses substantially more membrane transport proteins than was originally thought, and the analyses presented here provide a range of novel insights into the physiology of this important human pathogen.
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Affiliation(s)
- Rowena E Martin
- School of Biochemistry and Molecular Biology, Faculty of Science, The Australian National University, Canberra, ACT 0200, Australia
| | - Roselani I Henry
- School of Biochemistry and Molecular Biology, Faculty of Science, The Australian National University, Canberra, ACT 0200, Australia
| | - Janice L Abbey
- School of Biochemistry and Molecular Biology, Faculty of Science, The Australian National University, Canberra, ACT 0200, Australia
| | - John D Clements
- School of Biochemistry and Molecular Biology, Faculty of Science, The Australian National University, Canberra, ACT 0200, Australia
- Division of Neuroscience, The John Curtin School of Medical Research, The Australian National University, Canberra, ACT 0200, Australia
| | - Kiaran Kirk
- School of Biochemistry and Molecular Biology, Faculty of Science, The Australian National University, Canberra, ACT 0200, Australia
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46
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Landfear SM, Ullman B, Carter NS, Sanchez MA. Nucleoside and nucleobase transporters in parasitic protozoa. EUKARYOTIC CELL 2004; 3:245-54. [PMID: 15075255 PMCID: PMC387651 DOI: 10.1128/ec.3.2.245-254.2004] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Scott M Landfear
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon 97239-3098, USA.
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47
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Abstract
Parasites are responsible for a wide variety of infectious diseases in human as well as in domestic and wild animals, causing an enormous health and economical blight. Current containment strategies are not entirely successful and parasitic infections are on the rise. In the absence of availability of antiparasitic vaccines, chemotherapy remains the mainstay for the treatment of most parasitic diseases. However, there is an urgent need for new drugs to prevent or combat some major parasitic infections because of lack of a single effective approach for controlling the parasites (e.g., trypanosomiasis) or because some serious parasitic infections developed resistance to presently available drugs (e.g., malaria). The rational design of a drug is usually based on biochemical and physiological differences between pathogens and host. Some of the most striking differences between parasites and their mammalian host are found in purine metabolism. Purine nucleotides can be synthesized by the de novo and/or the so-called "salvage" pathways. Unlike their mammalian host, most parasites studied lack the pathways for de novo purine biosynthesis and rely on the salvage pathways to meet their purine demands. Moreover, because of the great phylogenic separation between the host and the parasite, there are in some cases sufficient distinctions between corresponding enzymes of the purine salvage from the host and the parasite that can be exploited to design specific inhibitors or "subversive substrates" for the parasitic enzymes. Furthermore, the specificities of purine transport, the first step in purine salvage, diverge significantly between parasites and their mammalian host. This review highlights the unique transporters and enzymes responsible for the salvage of purines in parasites that could constitute excellent potential targets for the design of safe and effective antiparasitic drugs.
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Affiliation(s)
- Mahmoud H el Kouni
- Department of Pharmacology and Toxicology, Center for AIDS Research, Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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48
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De Koning HP, Al-Salabi MI, Cohen AM, Coombs GH, Wastling JM. Identification and characterisation of high affinity nucleoside and nucleobase transporters in Toxoplasma gondii. Int J Parasitol 2003; 33:821-31. [PMID: 12865082 DOI: 10.1016/s0020-7519(03)00091-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The protozoan parasite Toxoplasma gondii depends upon salvaging the purines that it requires. We have re-analysed purine transport in T. gondii and identified novel nucleoside and nucleobase transporters. The latter transports hypoxanthine (TgNBT1; K(m)=0.91+/-0.19 microM) and is inhibited by guanine and xanthine: it is the first high affinity nucleobase transporter to be identified in an apicomplexan parasite. The previously reported nucleoside transporter, TgAT1, is low affinity with K(m) values of 105 and 134 microM for adenosine and inosine, respectively. We have now identified a second nucleoside transporter, TgAT2, which is high affinity and inhibited by adenosine, inosine, guanosine, uridine and thymidine (K(m) values 0.28-1.5 microM) as well as cytidine (K(i)=32 microM). TgAT2 also recognises several nucleoside analogues with therapeutic potential. We have investigated the basis for the broad specificity of TgAT2 and found that hydrogen bonds are formed with the 3' and 5' hydroxyl groups and that the base groups are bound through H-bonds with either N3 of the purine ring or N(3)H of the pyrimidine ring, and most probably pi-pi-stacking as well. The identification of these high affinity purine nucleobase and nucleoside transporters reconciles for the first time the low abundance of free nucleosides and nucleobases in the intracellular environment with the efficient purine salvage carried out by T. gondii.
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Affiliation(s)
- Harry P De Koning
- Division of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, UK.
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49
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Krishna S, Eckstein-Ludwig U, Joët T, Uhlemann AC, Morin C, Webb R, Woodrow C, Kun JFJ, Kremsner PG. Transport processes in Plasmodium falciparum-infected erythrocytes: potential as new drug targets. Int J Parasitol 2002; 32:1567-73. [PMID: 12435441 DOI: 10.1016/s0020-7519(02)00185-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Plasmodium falciparum infection induces alterations in the transport properties of infected erythrocytes that have recently been defined using electrophysiological techniques. Mechanisms responsible for transport of substrates into intraerythrocytic parasites have also been clarified by studies of three substrate-specific (hexose, nucleoside and aquaglyceroporin) parasite plasma membrane transporters. These have been characterised functionally using the Xenopus laevis oocyte heterologous expression system. The same expression system is currently being used to define the function of parasite 'P' type ATPases responsible for intraparasitic [Ca(2+)] homeostasis. We review studies on these transport processes and examine their potential as novel drug targets.
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Affiliation(s)
- Sanjeev Krishna
- Department of Infectious Diseases, St. George's Hospital Medical School, Cranmer Terrace, London, UK.
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50
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Saliba KJ, Kirk K. Nutrient acquisition by intracellular apicomplexan parasites: staying in for dinner. Int J Parasitol 2001; 31:1321-30. [PMID: 11566300 DOI: 10.1016/s0020-7519(01)00258-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The intracellular forms of the apicomplexan parasites Plasmodium, Toxoplasma and Eimeria reside within a parasitophorous vacuole. The nutrients required by these intracellular parasites to support their high rate of growth and replication originate from the host cell which, in turn, takes up such compounds from the extracellular milieu. Solutes moving from the external medium to the interior of the parasite, are confronted by a series of three membranes --the host cell membrane, the parasitophorous vacuole membrane and the parasite plasma membrane. Each constitutes a potential permeability barrier which must be either crossed or bypassed. It is the mechanisms by which this occurs that are the subject of this review.
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Affiliation(s)
- K J Saliba
- School of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, A.C.T. 0200, Australia
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