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García-Torres I, De la Mora-De la Mora I, López-Velázquez G, Cabrera N, Flores-López LA, Becker I, Herrera-López J, Hernández R, Pérez-Montfort R, Enríquez-Flores S. Repurposing of rabeprazole as an anti- Trypanosoma cruzi drug that targets cellular triosephosphate isomerase. J Enzyme Inhib Med Chem 2023; 38:2231169. [PMID: 37401012 PMCID: PMC10351538 DOI: 10.1080/14756366.2023.2231169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 06/23/2023] [Accepted: 06/25/2023] [Indexed: 07/05/2023] Open
Abstract
Trypanosoma cruzi is the causative agent of American trypanosomiasis, which mainly affects populations in Latin America. Benznidazole is used to control the disease, with severe effects in patients receiving this chemotherapy. Previous studies have demonstrated the inhibition of triosephosphate isomerase from T. cruzi, but cellular enzyme inhibition has yet to be established. This study demonstrates that rabeprazole inhibits both cell viability and triosephosphate isomerase activity in T. cruzi epimastigotes. Our results show that rabeprazole has an IC50 of 0.4 µM, which is 14.5 times more effective than benznidazole. Additionally, we observed increased levels of methyl-glyoxal and advanced glycation end products after the inhibition of cellular triosephosphate isomerase by rabeprazole. Finally, we demonstrate that the inactivation mechanisms of rabeprazole on triosephosphate isomerase of T. cruzi can be achieved through the derivatization of three of its four cysteine residues. These results indicate that rabeprazole is a promising candidate against American trypanosomiasis.
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Affiliation(s)
- Itzhel García-Torres
- Laboratorio de Biomoléculas y Salud Infantil, Instituto Nacional de Pediatría, CDMX, México
| | | | | | - Nallely Cabrera
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, CDMX, México
| | - Luis Antonio Flores-López
- CONAHCYT Instituto Nacional de Pediatría, Laboratorio de Biomoléculas y Salud Infantil, CDMX, México
| | - Ingeborg Becker
- Centro de Medicina Tropical, Unidad de Investigación en Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México, CDMX, México
| | - Juliana Herrera-López
- Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, CDMX, México
| | - Roberto Hernández
- Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, CDMX, México
| | - Ruy Pérez-Montfort
- Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, CDMX, México
| | - Sergio Enríquez-Flores
- Laboratorio de Biomoléculas y Salud Infantil, Instituto Nacional de Pediatría, CDMX, México
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Nikolaev DM, Mironov VN, Shtyrov AA, Kvashnin ID, Mereshchenko AS, Vasin AV, Panov MS, Ryazantsev MN. Fluorescence Imaging of Cell Membrane Potential: From Relative Changes to Absolute Values. Int J Mol Sci 2023; 24:ijms24032435. [PMID: 36768759 PMCID: PMC9916766 DOI: 10.3390/ijms24032435] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Revised: 01/20/2023] [Accepted: 01/23/2023] [Indexed: 01/28/2023] Open
Abstract
Membrane potential is a fundamental property of biological cells. Changes in membrane potential characterize a vast number of vital biological processes, such as the activity of neurons and cardiomyocytes, tumorogenesis, cell-cycle progression, etc. A common strategy to record membrane potential changes that occur in the process of interest is to utilize organic dyes or genetically-encoded voltage indicators with voltage-dependent fluorescence. Sensors are introduced into target cells, and alterations of fluorescence intensity are recorded with optical methods. Techniques that allow recording relative changes of membrane potential and do not take into account fluorescence alterations due to factors other than membrane voltage are already widely used in modern biological and biomedical studies. Such techniques have been reviewed previously in many works. However, in order to investigate a number of processes, especially long-term processes, the measured signal must be corrected to exclude the contribution from voltage-independent factors or even absolute values of cell membrane potential have to be evaluated. Techniques that enable such measurements are the subject of this review.
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Affiliation(s)
- Dmitrii M. Nikolaev
- Institute of Biomedical Systems and Biotechnologies, Peter the Great Saint Petersburg Polytechnic University, 29 Polytechnicheskaya str., 195251 Saint Petersburg, Russia
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
| | - Vladimir N. Mironov
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
| | - Andrey A. Shtyrov
- Institute of Biomedical Systems and Biotechnologies, Peter the Great Saint Petersburg Polytechnic University, 29 Polytechnicheskaya str., 195251 Saint Petersburg, Russia
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
| | - Iaroslav D. Kvashnin
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
| | - Andrey S. Mereshchenko
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 Saint Petersburg, Russia
| | - Andrey V. Vasin
- Institute of Biomedical Systems and Biotechnologies, Peter the Great Saint Petersburg Polytechnic University, 29 Polytechnicheskaya str., 195251 Saint Petersburg, Russia
| | - Maxim S. Panov
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 Saint Petersburg, Russia
- Center for Biophysical Studies, Saint Petersburg State Chemical Pharmaceutical University, 14 Professor Popov str., lit. A, 197022 Saint Petersburg, Russia
| | - Mikhail N. Ryazantsev
- Nanotechnology Research and Education Centre RAS, Saint Petersburg Academic University, 8/3 Khlopina str., 194021 Saint Petersburg, Russia
- Institute of Chemistry, Saint Petersburg State University, 26 Universitetskii pr, 198504 Saint Petersburg, Russia
- Correspondence:
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3
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Greene AS, Hajduk SL. Trypanosome Lytic Factor-1 Initiates Oxidation-stimulated Osmotic Lysis of Trypanosoma brucei brucei. J Biol Chem 2016; 291:3063-75. [PMID: 26645690 PMCID: PMC4742767 DOI: 10.1074/jbc.m115.680371] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Revised: 11/12/2015] [Indexed: 01/18/2023] Open
Abstract
Human innate immunity against the veterinary pathogen Trypanosoma brucei brucei is conferred by trypanosome lytic factors (TLFs), against which human-infective T. brucei gambiense and T. brucei rhodesiense have evolved resistance. TLF-1 is a subclass of high density lipoprotein particles defined by two primate-specific apolipoproteins: the ion channel-forming toxin ApoL1 (apolipoprotein L1) and the hemoglobin (Hb) scavenger Hpr (haptoglobin-related protein). The role of oxidative stress in the TLF-1 lytic mechanism has been controversial. Here we show that oxidative processes are involved in TLF-1 killing of T. brucei brucei. The lipophilic antioxidant N,N'-diphenyl-p-phenylenediamine protected TLF-1-treated T. brucei brucei from lysis. Conversely, lysis of TLF-1-treated T. brucei brucei was increased by the addition of peroxides or thiol-conjugating agents. Previously, the Hpr-Hb complex was postulated to be a source of free radicals during TLF-1 lysis. However, we found that the iron-containing heme of the Hpr-Hb complex was not involved in TLF-1 lysis. Furthermore, neither high concentrations of transferrin nor knock-out of cytosolic lipid peroxidases prevented TLF-1 lysis. Instead, purified ApoL1 was sufficient to induce lysis, and ApoL1 lysis was inhibited by the antioxidant DPPD. Swelling of TLF-1-treated T. brucei brucei was reminiscent of swelling under hypotonic stress. Moreover, TLF-1-treated T. brucei brucei became rapidly susceptible to hypotonic lysis. T. brucei brucei cells exposed to peroxides or thiol-binding agents were also sensitized to hypotonic lysis in the absence of TLF-1. We postulate that ApoL1 initiates osmotic stress at the plasma membrane, which sensitizes T. brucei brucei to oxidation-stimulated osmotic lysis.
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Affiliation(s)
- Amy Styer Greene
- From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602
| | - Stephen L Hajduk
- From the Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602
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Steinmann ME, González-Salgado A, Bütikofer P, Mäser P, Sigel E. A heteromeric potassium channel involved in the modulation of the plasma membrane potential is essential for the survival of African trypanosomes. FASEB J 2015; 29:3228-37. [DOI: 10.1096/fj.15-271353] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Accepted: 03/31/2015] [Indexed: 11/11/2022]
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Jimenez V, Docampo R. Molecular and electrophysiological characterization of a novel cation channel of Trypanosoma cruzi. PLoS Pathog 2012; 8:e1002750. [PMID: 22685407 PMCID: PMC3369953 DOI: 10.1371/journal.ppat.1002750] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2012] [Accepted: 04/27/2012] [Indexed: 01/27/2023] Open
Abstract
We report the identification, functional expression, purification, reconstitution and electrophysiological characterization of a novel cation channel (TcCat) from Trypanosoma cruzi, the etiologic agent of Chagas disease. This channel is potassium permeable and shows inward rectification in the presence of magnesium. Western blot analyses with specific antibodies indicated that the protein is expressed in the three main life cycle stages of the parasite. Surprisingly, the parasites have the unprecedented ability to rapidly change the localization of the channel when they are exposed to different environmental stresses. TcCat rapidly translocates to the tip of the flagellum when trypomastigotes are submitted to acidic pH, to the plasma membrane when epimastigotes are submitted to hyperosmotic stress, and to the cell surface when amastigotes are released to the extracellular medium. Pharmacological block of TcCat activity also resulted in alterations in the trypomastigotes ability to respond to hyperosmotic stress. We also demonstrate the feasibility of purifying and reconstituting a functional ion channel from T. cruzi after recombinant expression in bacteria. The peculiar characteristics of TcCat could be important for the development of specific inhibitors with therapeutic potential against trypanosomes. The use of high-resolution electrophysiological techniques to study ion channels has provided a large amount of information on functional aspects of these important membrane proteins. However, the study of ion channels in unicellular eukaryotes has been limited to detection of ion conductances in large cells, gene identification studies, and pharmacological treatments to investigate the potential presence of different ion channels. In this paper we report the first identification, functional expression, purification, reconstitution, and electrophysiological characterization with single-molecule resolution of a novel cation channel (TcCat) from Trypanosoma cruzi. This is a novel channel that shares little sequence and functional similarities to other potassium channels and its peculiar characteristics could be important for the development of specific inhibitors with therapeutic potential against trypanosomiasis. Surprisingly, the parasites have the unprecedented ability to rapidly change the localization of the channel when they are exposed to different environmental stresses. We demonstrated the feasibility of purifying and reconstituting a functional ion channel from T. cruzi after recombinant expression in bacteria. In addition, we obtained yeast mutants that will provide a useful genetic system for studies of the assembly and composition of the channel.
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Affiliation(s)
- Veronica Jimenez
- Center for Tropical and Emerging Global Diseases and Department of Cellular Biology, University of Georgia, Athens, Georgia, United States of America
- * E-mail: (VJ); (RD)
| | - Roberto Docampo
- Center for Tropical and Emerging Global Diseases and Department of Cellular Biology, University of Georgia, Athens, Georgia, United States of America
- * E-mail: (VJ); (RD)
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6
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Abstract
The molecular mechanisms of K(+) homeostasis are only poorly understood for protozoan parasites. Trypanosoma brucei subsp. parasites, the causative agents of human sleeping sickness and nagana, are strictly extracellular and need to actively concentrate K(+) from their hosts' body fluids. The T. brucei genome contains two putative K(+) channel genes, yet the trypanosomes are insensitive to K(+) antagonists and K(+) channel-blocking agents, and they do not spontaneously depolarize in response to high extracellular K(+) concentrations. However, the trypanosomes are extremely sensitive to K(+) ionophores such as valinomycin. Surprisingly, T. brucei possesses a member of the Trk/HKT superfamily of monovalent cation permeases which so far had only been known from bacteria, archaea, fungi, and plants. The protein was named TbHKT1 and functions as a Na(+)-independent K(+) transporter when expressed in Escherichia coli, Saccharomyces cerevisiae, or Xenopus laevis oocytes. In trypanosomes, TbHKT1 is expressed in both the mammalian bloodstream stage and the Tsetse fly midgut stage; however, RNA interference (RNAi)-mediated silencing of TbHKT1 expression did not produce a growth phenotype in either stage. The presence of HKT genes in trypanosomatids adds a further piece to the enigmatic phylogeny of the Trk/HKT superfamily of K(+) transporters. Parsimonial analysis suggests that the transporters were present in the first eukaryotes but subsequently lost in several of the major eukaryotic lineages, in at least four independent events.
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7
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Klapperstück T, Glanz D, Klapperstück M, Wohlrab J. Methodological aspects of measuring absolute values of membrane potential in human cells by flow cytometry. Cytometry A 2009; 75:593-608. [PMID: 19504578 DOI: 10.1002/cyto.a.20735] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The bis-barbituric acid oxonol, DiBAC(4)(3) is used as a standard potentiometric probe in human cells. However, its fluorescence depends not only on membrane potential but also varies with nonpotential related changes in the amount of intracellular free and bound dye. This study demonstrates the influence of different experimental conditions on this nonspecific fluorescence proportion. IGR1 melanoma cells as a model were specifically altered in cell volume and protein content by depolarizing treatments or cell cycle synchronization. Flow cytometry was performed over a wide range of extracellular DiBAC(4)(3) concentrations. Fixation and increase in protein content led to a nonspecifically enhanced fluorescence, while changes in the amount of free intracellular dye as a result of altered cell volume proved to be negligible. To establish a calibration curve using totally depolarized cells, the pore-forming action of gramicidin should be preferred to fixation. Below 100 nM DiBAC(4)(3), the logarithmic relation between cell fluorescence and dye concentration turned into a virtually linear function intersecting with zero. Consequently, calibration can then be confined to determination of the fluorescence of depolarized cells stained with the same concentration as used for the actual measurement of membrane potential. Unexpectedly, quenching of fluorescence occurred in totally depolarized cells at concentrations higher than 6,250 nM. Linearity and quenching could be confirmed by additional experiments on Chinese hamster ovary CHO-K1 and B lymphoblastoid LCL-HO cells.
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Affiliation(s)
- Thomas Klapperstück
- Department of Dermatology and Venereology, Martin Luther University of Halle-Wittenberg, Saale, Germany.
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8
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Galvez Rojas RL, Frossard ML, Machado Motta MC, Silber AM. l-Proline uptake in Crithidia deanei is influenced by its endosymbiont bacterium. FEMS Microbiol Lett 2008; 283:15-22. [DOI: 10.1111/j.1574-6968.2008.01125.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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9
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Allen RJW, Kirk K. The membrane potential of the intraerythrocytic malaria parasite Plasmodium falciparum. J Biol Chem 2003; 279:11264-72. [PMID: 14630911 DOI: 10.1074/jbc.m311110200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The membrane potential (Deltapsi) of the mature asexual form of the human malaria parasite, Plasmodium falciparum, isolated from its host erythrocyte using a saponin permeabilization technique, was investigated using both the radiolabeled Deltapsi indicator tetraphenylphosphonium ([(3)H]TPP(+)) and the fluorescent Deltapsi indicator DiBAC(4)(3) (bis-oxonol). For isolated parasites suspended in a high Na(+), low K(+) solution, Deltapsi was estimated from the measured distribution of [(3)H]TPP(+) to be -95 +/- 2 mV. Deltapsi was reduced by the specific V-type H(+) pump inhibitor bafilomycin A(1), by the H(+) ionophore CCCP, and by glucose deprivation. Acidification of the parasite cytosol (induced by the addition of lactate) resulted in a transient hyperpolarization, whereas a cytosolic alkalinization (induced by the addition of NH(4)(+)) resulted in a transient depolarization. A decrease in the extracellular pH resulted in a membrane depolarization, whereas an increase in the extracellular pH resulted in a membrane hyperpolarization. The parasite plasma membrane depolarized in response to an increase in the extracellular K(+) concentration and hyperpolarized in response to a decrease in the extracellular K(+) concentration and to the addition of the K(+) channel blockers Ba(2+) or Cs(+) to the suspending medium. The data are consistent with Deltapsi of the intraerythrocytic P. falciparum trophozoite being due to the electrogenic extrusion of H(+) via the V-type H(+) pump at the parasite surface. The current associated with the efflux of H(+) is countered, in part, by the influx of K(+) via Ba(2+)- and Cs(+)-sensitive K(+) channels in the parasite plasma membrane.
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Affiliation(s)
- Richard J W Allen
- School of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, Australian Capital Territory 0200, Australia
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10
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Van der Heyden N, Docampo R. Significant differences between procyclic and bloodstream forms of Trypanosoma brucei in the maintenance of their plasma membrane potential. J Eukaryot Microbiol 2002; 49:407-13. [PMID: 12425529 DOI: 10.1111/j.1550-7408.2002.tb00220.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The plasma membrane potential (deltapsi) of procyclic and bloodstream trypomastigotes of Trypanosoma brucei was studied using the potentiometric fluorescent dye bisoxonol. Our results suggest that a proton pump plays a significant role in the regulation of deltapsi in procyclic and bloodstream forms, as evidenced by depolarization of the plasma membrane by H(+)-ATPase inhibitors (e.g. dicyclohexylcarbo-diimide, N-ethylmaleimide, diethylstilbestrol, and bafilomycin A1). In bloodstream stages the plasma membrane was significantly depolarized by ouabain only when the cells were incubated in sodium-rich buffers indicating that a sodium pump was being inhibited. In contrast, ouabain had no effect on the deltapsi of the procyclic stages in a sodium-rich buffer. However, it induced an additional significant depolarization in these stages when their plasma membrane was already partially depolarized by the H(+)-ATPase inhibitor dicyclohexylcarbo-diimide, indicating the presence of an ouabain-sensitive sodium pump whose activity is masked by the H(+)-ATPase. Unlike procyclic forms, the deltapsi of bloodstream-stage trypomastigotes was markedly sensitive to extracellular Na+ and K+ concentrations. Thus, there are significant differences between procyclic and bloodstream forms in the maintenance of the deltapsi and in their permeability to cations.
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11
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Abstract
Purines and pyrimidines play a key role in nucleic acid and nucleotide metabolism of all cells. In addition, they can be used as nitrogen sources in plants and many microorganisms. Transport of nucleobases across biological membranes is mediated by specific transmembrane transport proteins. Nucleobase transporters have been identified genetically and/or physiologically in bacteria, fungi, protozoa, algae, plants and mammals. A limited number of bacterial and fungal transporter genes have been cloned and analysed in great detail at the molecular level. Very recently, nucleobase transporters have been identified in plants. In other systems, with less accessible genetics, such as vertebrates and protozoa, no nucleobase transporter genes have been identified, and the transporters have been characterized and classified by physiological and biochemical approaches instead. In this review, it is shown that nucleobase transporters and similar sequences of unknown function present in databases constitute three basic families, which will be designated NAT, PRT and PUP. The first includes members from archea, eubacteria, fungi, plants and metazoa, the second is restricted to prokaryotes and fungi, and the last one is only found in plants. Interestingly, mammalian ascorbate transporters are homologous to NAT sequences. The function of different nucleobase transporters is also described, as is how their expression is regulated and what is currently known about their structure-function relationships. Common features emerging from these studies are expected to prove critical in understanding what governs nucleobase transporter specificity and in selecting proper model microbial systems for cloning and studying plant, protozoan and mammalian nucleobase transporters of agricultural, pharmacological and medical importance.
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Affiliation(s)
- H de Koning
- Institute of Biomedical and Life Sciences, University of Glasgow, UK
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12
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Vieira LL. pH and volume homeostasis in trypanosomatids: current views and perspectives. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1376:221-41. [PMID: 9748588 DOI: 10.1016/s0304-4157(98)00007-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- L L Vieira
- Department of Cell Biology, Institute of Experimental Biology, Faculty of Science, Universidad Central de Venezuela, Caracas 47069, Venezuela
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13
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de Koning HP, Watson CJ, Jarvis SM. Characterization of a nucleoside/proton symporter in procyclic Trypanosoma brucei brucei. J Biol Chem 1998; 273:9486-94. [PMID: 9545276 DOI: 10.1074/jbc.273.16.9486] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adenosine transport at 22 degrees C in procyclic forms of Trypanosoma brucei brucei was investigated using an oil-inhibitor stop procedure for determining initial rates of adenosine uptake in suspended cells. Adenosine influx was mediated by a single high affinity transporter (Km 0.26 +/- 0.02 microM, Vmax 0.63 +/- 0.18 pmol/10(7) cells s-1). Purine nucleosides, with the exception of tubercidin (7-deazaadenosine), and dipyridamole inhibited adenosine influx (Ki 0.18-5.2 microM). Purine nucleobases and pyrimidine nucleosides and nucleobases had no effect on adenosine transport. This specificity of the transporter appears to be similar to the previously described P1 adenosine transporter in bloodstream forms of trypanosomes. Uptake of adenosine was Na+-independent, but ionophores reducing the membrane potential and/or the transmembrane proton gradient (monitored with the fluorescent probes bis-(1,3-diethylthiobarbituric acid)-trimethine oxonol and 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein acetoxymethyl ester, respectively) inhibited adenosine transport. Similarly, an increase in extracellular pH from 7.3 to 8.0 reduced adenosine influx by 30%. A linear correlation was demonstrated between the rate of adenosine transport and the protonmotive force. Adenosine uptake was accompanied by a proton influx in base-loaded cells and was also shown to be electrogenic. These combined results indicate that transport of adenosine in T. brucei brucei procyclics is protonmotive force-driven and strongly suggest that the adenosine transporter functions as an H+ symporter.
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Affiliation(s)
- H P de Koning
- Research School of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, United Kingdom
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14
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de Koning HP, Jarvis SM. Purine nucleobase transport in bloodstream forms of Trypanosoma brucei is mediated by two novel transporters. Mol Biochem Parasitol 1997; 89:245-58. [PMID: 9364969 DOI: 10.1016/s0166-6851(97)00129-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The mechanism and inhibitor sensitivity of hypoxanthine transport by bloodstream forms of Trypanosoma brucei brucei was investigated. The dose response curve for the inhibition of hypoxanthine transport (1 microM) by guanosine was biphasic; approximately 90% of transport activity was inhibited with a Ki value of 10.8 +/- 1.8 microM, but 10% of the activity remained insensitive to concentrations as high as 2 mM. These two components of hypoxanthine transport are defined as guanosine-sensitive (H2) and guanosine-insensitive (H3). Hypoxanthine influx by both components was saturable, but there was a marked difference in their Km values (123 +/- 15 nM and 4.7 +/- 0.9 microM for H2 and H3, respectively) although the Vmax values (1.1 +/- 0.2 and 1.1 +/- 0.1 pmol (10[7] cells)[-1] s[-1], n = 3) were similar. Hypoxanthine uptake via the H2 carrier was inhibited by purine bases and analogues as well as by some pyrimidine bases and one nucleoside (guanosine), whereas the H3 transporter was sensitive only to inhibition by purine nucleobases. H2-mediated hypoxanthine uptake was inhibited by ionophores, ion exchangers and the potential H+-ATPase inhibitors, N,N'-dicyclohexylcarbodiimide (DCCD) and N-ethylmaleimide (NEM). Measurements of the intracellular pH and membrane potential of bloodstream trypanosomes in the presence and absence of these agents established a linear correlation between protonmotive force and rate of [3H]hypoxanthine (30 nM) uptake. We conclude that hypoxanthine transport in bloodstream forms of T. b. brucei occurs by two transport systems with different affinities and substrate specificities, one of which, H2, appears to function as a H+-/hypoxanthine symporter.
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Affiliation(s)
- H P de Koning
- Research School of Biosciences, University of Kent at Canterbury, UK
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15
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de Koning HP, Jarvis SM. Hypoxanthine uptake through a purine-selective nucleobase transporter in Trypanosoma brucei brucei procyclic cells is driven by protonmotive force. EUROPEAN JOURNAL OF BIOCHEMISTRY 1997; 247:1102-10. [PMID: 9288936 DOI: 10.1111/j.1432-1033.1997.01102.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The mechanism of purine nucleobase transport in procyclic cells of the protozoan parasite Trypanosoma brucei brucei was investigated. Hypoxanthine uptake at 22 degrees C was rapid and saturable, exhibiting an apparent Km of 9.3 +/- 2.0 microM and a Vmax of 4.5 +/- 0.8 pmol x (10(7) cells)(-1) x s(-1). All the natural purine nucleobases tested (Ki 1.8-7.2 microM), as well as the purine analogues oxypurinol and allopurinol, inhibited hypoxanthine influx in a manner consistent with the presence of a single high-affinity carrier. Nucleosides and pyrimidine nucleobases had little or no effect on hypoxanthine influx. The uptake process was independent of extracellular sodium, but inhibited by ionophores inducing cytosolic acidification (carbonyl cyanide chlorophenylhydrazone, nigericin, valinomycin) or membrane depolarisation (gramicidin) as well as by the adenosine triphosphatase inhibitors N-ethylmaleimide and N,N'-dicyclohexylcarbodiimide. Using the fluorescent dyes bisoxonol and 2',7'-bis-(carboxyethyl)-5,6-carboxy-fluorescein to determine membrane potential and intracellular pH (pHi), the rate of hypoxanthine uptake was shown to be directly proportional to the protonmotive force. Similarly, under alkaline extracellular conditions hypoxanthine uptake was reversibly inhibited alongside a reduction in protonmotive force. In addition, hypoxanthine accelerated the rate of pH, recovery to pH 7 after base-loading with NH4Cl, indicative of a proton influx concurrent with hypoxanthine transport. Finally, after pretreatment of cells with N-ethylmaleimide, hypoxanthine induced a slow membrane depolarisation, demonstrating that hypoxanthine transport is electrogenic. These data show that hypoxanthine uptake in T. b. brucei procyclic cells is dependent on the protonmotive force, and are consistent with a nucleobase/H+-symporter model for this transporter.
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Affiliation(s)
- H P de Koning
- Research School of Biosciences, University of Kent, Canterbury, United Kingdom
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