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Piro F, Masci S, Kannan G, Focaia R, Schultz TL, Thaprawat P, Carruthers VB, Di Cristina M. A Toxoplasma gondii putative amino acid transporter localizes to the plant-like vacuolar compartment and controls parasite extracellular survival and stage differentiation. mSphere 2024; 9:e0059723. [PMID: 38051073 PMCID: PMC10871165 DOI: 10.1128/msphere.00597-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Accepted: 10/26/2023] [Indexed: 12/07/2023] Open
Abstract
Toxoplasma gondii is a protozoan parasite that infects a broad spectrum of hosts and can colonize many organs and cell types. The ability to reside within a wide range of different niches requires substantial adaptability to diverse microenvironments. Very little is known about how this parasite senses various milieus and adapts its metabolism to survive, replicate during the acute stage, and then differentiate to the chronic stage. T. gondii possesses a lysosome-like organelle known as the plant-like vacuolar compartment (PLVAC), which serves various functions, including digestion, ion storage and homeostasis, endocytosis, and autophagy. Lysosomes are critical for maintaining cellular health and function by degrading waste materials and recycling components. To supply the cell with the essential building blocks and energy sources required for the maintenance of its functions and structures, the digested solutes generated within the lysosome are transported into the cytosol by proteins embedded in the lysosomal membrane. Currently, a limited number of PLVAC transporters have been characterized, with TgCRT being the sole potential transporter of amino acids and small peptides identified thus far. To bridge this knowledge gap, we used lysosomal amino acid transporters from other organisms as queries to search the T. gondii proteome. This led to the identification of four potential amino acid transporters, which we have designated as TgAAT1-4. Assessing their expression and sub-cellular localization, we found that one of them, TgAAT1, localized to the PLVAC and is necessary for normal parasite extracellular survival and bradyzoite differentiation. Moreover, we present preliminary data showing the possible involvement of TgAAT1 in the PLVAC transport of arginine.IMPORTANCEToxoplasma gondii is a highly successful parasite infecting a broad range of warm-blooded organisms, including about one-third of all humans. Although Toxoplasma infections rarely result in symptomatic disease in individuals with a healthy immune system, the incredibly high number of persons infected, along with the risk of severe infection in immunocompromised patients and the potential link of chronic infection to mental disorders, makes this infection a significant public health concern. As a result, there is a pressing need for new treatment approaches that are both effective and well tolerated. The limitations in understanding how Toxoplasma gondii manages its metabolism to adapt to changing environments and triggers its transformation into bradyzoites have hindered the discovery of vulnerabilities in its metabolic pathways or nutrient acquisition mechanisms to identify new therapeutic targets. In this work, we have shown that the lysosome-like organelle plant-like vacuolar compartment (PLVAC), acting through the putative arginine transporter TgAAT1, plays a pivotal role in regulating the parasite's extracellular survival and differentiation into bradyzoites.
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Affiliation(s)
- Federica Piro
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Silvia Masci
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Geetha Kannan
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Riccardo Focaia
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Tracey L. Schultz
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Pariyamon Thaprawat
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Vern B. Carruthers
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Manlio Di Cristina
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
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2
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Down the membrane hole: Ion channels in protozoan parasites. PLoS Pathog 2022; 18:e1011004. [PMID: 36580479 PMCID: PMC9799330 DOI: 10.1371/journal.ppat.1011004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Parasitic diseases caused by protozoans are highly prevalent around the world, disproportionally affecting developing countries, where coinfection with other microorganisms is common. Control and treatment of parasitic infections are constrained by the lack of specific and effective drugs, plus the rapid emergence of resistance. Ion channels are main drug targets for numerous diseases, but their potential against protozoan parasites is still untapped. Ion channels are membrane proteins expressed in all types of cells, allowing for the flow of ions between compartments, and regulating cellular functions such as membrane potential, excitability, volume, signaling, and death. Channels and transporters reside at the interface between parasites and their hosts, controlling nutrient uptake, viability, replication, and infectivity. To understand how ion channels control protozoan parasites fate and to evaluate their suitability for therapeutics, we must deepen our knowledge of their structure, function, and modulation. However, methodological approaches commonly used in mammalian cells have proven difficult to apply in protozoans. This review focuses on ion channels described in protozoan parasites of clinical relevance, mainly apicomplexans and trypanosomatids, highlighting proteins for which molecular and functional evidence has been correlated with their physiological functions.
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3
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Stasic AJ, Moreno SNJ, Carruthers VB, Dou Z. The Toxoplasma plant-like vacuolar compartment (PLVAC). J Eukaryot Microbiol 2022; 69:e12951. [PMID: 36218001 PMCID: PMC10576567 DOI: 10.1111/jeu.12951] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Revised: 10/06/2022] [Accepted: 10/07/2022] [Indexed: 11/28/2022]
Abstract
Toxoplasma gondii belongs to the phylum Apicomplexa and is an important cause of congenital disease and infection in immunocompromised patients. T. gondii shares several characteristics with plants including a nonphotosynthetic plastid termed apicoplast and a multivesicular organelle that was named the plant-like vacuole (PLV) or vacuolar compartment (VAC). The name plant-like vacuole was selected based on its resemblance in composition and function to plant vacuoles. The name VAC represents its general vacuolar characteristics. We will refer to the organelle as PLVAC in this review. New findings in recent years have revealed that the PLVAC represents the lysosomal compartment of T. gondii which has adapted peculiarities to fulfill specific Toxoplasma needs. In this review, we discuss the composition and functions of the PLVAC highlighting its roles in ion storage and homeostasis, endocytosis, exocytosis, and autophagy.
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Affiliation(s)
- Andrew J Stasic
- Department of Microbiology, Heartland FPG, Carmel, Indiana, USA
| | - Silvia N J Moreno
- Department of Cellular Biology, University of Georgia, Georgia, Athens, USA
- Center for Tropical and Emerging Global Diseases and Department of Cellular Biology, University of Georgia, Georgia, Athens, USA
| | - Vern B Carruthers
- Department of Microbiology & Immunology, University of Michigan Medical School, Michigan, Ann Arbor, USA
| | - Zhicheng Dou
- Department of Biological Sciences, Clemson University, South Carolina, Clemson, USA
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4
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Keon KA, Benlekbir S, Kirsch SH, Müller R, Rubinstein JL. Cryo-EM of the Yeast V O Complex Reveals Distinct Binding Sites for Macrolide V-ATPase Inhibitors. ACS Chem Biol 2022; 17:619-628. [PMID: 35148071 DOI: 10.1021/acschembio.1c00894] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Vacuolar-type adenosine triphosphatases (V-ATPases) are proton pumps found in almost all eukaryotic cells. These enzymes consist of a soluble catalytic V1 region that hydrolyzes ATP and a membrane-embedded VO region responsible for proton translocation. V-ATPase activity leads to acidification of endosomes, phagosomes, lysosomes, secretory vesicles, and the trans-Golgi network, with extracellular acidification occurring in some specialized cells. Small-molecule inhibitors of V-ATPase have played a crucial role in elucidating numerous aspects of cell biology by blocking acidification of intracellular compartments, while therapeutic use of V-ATPase inhibitors has been proposed for the treatment of cancer, osteoporosis, and some infections. Here, we determine structures of the isolated VO complex from Saccharomyces cerevisiae bound to two well-known macrolide inhibitors: bafilomycin A1 and archazolid A. The structures reveal different binding sites for the inhibitors on the surface of the proton-carrying c ring, with only a small amount of overlap between the two sites. Binding of both inhibitors is mediated primarily through van der Waals interactions in shallow pockets and suggests that the inhibitors block rotation of the ring. Together, these structures indicate the existence of a large chemical space available for V-ATPase inhibitors that block acidification by binding the c ring.
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Affiliation(s)
- Kristine A. Keon
- Molecular Medicine Program, The Hospital for Sick Children, Toronto, Canada M5G0A4
- Department of Medical Biophysics, The University of Toronto, Toronto, Canada M5G1L7
| | - Samir Benlekbir
- Molecular Medicine Program, The Hospital for Sick Children, Toronto, Canada M5G0A4
| | - Susanne H. Kirsch
- Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research (HZI), Saarland University Campus, 66123 Saarbrücken, Germany
| | - Rolf Müller
- Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research (HZI) and Department of Pharmacy, Saarland University Campus, 66123 Saarbrücken, Germany
| | - John L. Rubinstein
- Molecular Medicine Program, The Hospital for Sick Children, Toronto, Canada M5G0A4
- Department of Medical Biophysics, The University of Toronto, Toronto, Canada M5G1L7
- Department of Biochemistry, The University of Toronto, Toronto, Canada M5S1A8
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5
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Hayward JA, Rajendran E, Makota FV, Bassett BJ, Devoy M, Neeman T, van Dooren GG. Real-Time Analysis of Mitochondrial Electron Transport Chain Function in Toxoplasma gondii Parasites Using a Seahorse XFe96 Extracellular Flux Analyzer. Bio Protoc 2022; 12:e4288. [PMID: 35118179 PMCID: PMC8769764 DOI: 10.21769/bioprotoc.4288] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 11/04/2021] [Accepted: 11/07/2021] [Indexed: 07/22/2023] Open
Abstract
The mitochondrial electron transport chain (ETC) performs several critical biological functions, including maintaining mitochondrial membrane potential, serving as an electron sink for important metabolic pathways, and contributing to the generation of ATP via oxidative phosphorylation. The ETC is important for the survival of many eukaryotic organisms, including intracellular parasites such as the apicomplexan Toxoplasma gondii. The ETC of T. gondii and related parasites differs in several ways from the ETC of the mammalian host cells they infect, and can be targeted by anti-parasitic drugs, including the clinically used compound atovaquone. To characterize the function of novel ETC proteins found in the parasite and to identify new ETC inhibitors, a scalable assay that assesses both ETC function and non-mitochondrial parasite metabolism (e.g., glycolysis) is desirable. Here, we describe methods to measure the oxygen consumption rate (OCR) of intact T. gondii parasites and thereby assess ETC function, while simultaneously measuring the extracellular acidification rate (ECAR) as a measure of general parasite metabolism, using a Seahorse XFe96 extracellular flux analyzer. We also describe a method to pinpoint the location of ETC defects and/or the targets of inhibitors, using permeabilized T. gondii parasites. We have successfully used these methods to investigate the function of T. gondii proteins, including the apicomplexan parasite-specific protein subunit TgQCR11 of the coenzyme Q:cytochrome c oxidoreductase complex (ETC Complex III). We note that these methods are also amenable to screening compound libraries to identify candidate ETC inhibitors.
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Affiliation(s)
- Jenni A. Hayward
- Research School of Biology, Australian National University, Canberra, Australia
| | - Esther Rajendran
- Research School of Biology, Australian National University, Canberra, Australia
| | - F. Victor Makota
- Research School of Biology, Australian National University, Canberra, Australia
| | - Brad J. Bassett
- Research School of Biology, Australian National University, Canberra, Australia
| | - Michael Devoy
- Flow Cytometry Facility, The John Curtin School of Medical Research, Australian National University, Canberra, Australia
| | - Teresa Neeman
- Biological Data Science Institute, The Australian National University, Canberra, Australia
| | - Giel G. van Dooren
- Research School of Biology, Australian National University, Canberra, Australia
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6
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Fairweather SJ, Rajendran E, Blume M, Javed K, Steinhöfel B, McConville MJ, Kirk K, Bröer S, van Dooren GG. Coordinated action of multiple transporters in the acquisition of essential cationic amino acids by the intracellular parasite Toxoplasma gondii. PLoS Pathog 2021; 17:e1009835. [PMID: 34432856 PMCID: PMC8423306 DOI: 10.1371/journal.ppat.1009835] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Revised: 09/07/2021] [Accepted: 07/23/2021] [Indexed: 02/07/2023] Open
Abstract
Intracellular parasites of the phylum Apicomplexa are dependent on the scavenging of essential amino acids from their hosts. We previously identified a large family of apicomplexan-specific plasma membrane-localized amino acid transporters, the ApiATs, and showed that the Toxoplasma gondii transporter TgApiAT1 functions in the selective uptake of arginine. TgApiAT1 is essential for parasite virulence, but dispensable for parasite growth in medium containing high concentrations of arginine, indicating the presence of at least one other arginine transporter. Here we identify TgApiAT6-1 as the second arginine transporter. Using a combination of parasite assays and heterologous characterisation of TgApiAT6-1 in Xenopus laevis oocytes, we demonstrate that TgApiAT6-1 is a general cationic amino acid transporter that mediates both the high-affinity uptake of lysine and the low-affinity uptake of arginine. TgApiAT6-1 is the primary lysine transporter in the disease-causing tachyzoite stage of T. gondii and is essential for parasite proliferation. We demonstrate that the uptake of cationic amino acids by TgApiAT6-1 is ‘trans-stimulated’ by cationic and neutral amino acids and is likely promoted by an inwardly negative membrane potential. These findings demonstrate that T. gondii has evolved overlapping transport mechanisms for the uptake of essential cationic amino acids, and we draw together our findings into a comprehensive model that highlights the finely-tuned, regulated processes that mediate cationic amino acid scavenging by these intracellular parasites. The causative agent of toxoplasmosis, Toxoplasma gondii, is a versatile intracellular parasite that can proliferate within nucleated cells of warm-blooded organisms. In order to survive, T. gondii parasites must scavenge the cationic amino acids lysine and arginine from their hosts. In a previous study, we demonstrated that a plasma membrane-localized protein called TgApiAT1 facilitates the uptake of arginine into the parasite. We found that parasites lacking TgApiAT1 could proliferate when cultured in medium containing high concentrations of arginine, suggesting the existence of an additional uptake pathway for arginine. In the present study, we demonstrate that this second uptake pathway is mediated by TgApiAT6-1, a protein belonging to the same solute transporter family as TgApiAT1. We show that TgApiAT6-1 is the major lysine transporter of the parasite, and that it is critical for parasite proliferation. Furthermore, we demonstrate that TgApiAT6-1 can transport arginine into parasites under conditions in which arginine concentrations are high and lysine concentrations are comparatively lower. These data support a model for the finely-tuned acquisition of essential cationic amino acids that involves multiple transporters, and which likely contributes to these parasites being able to survive and proliferate within a wide variety of host cell types.
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Affiliation(s)
- Stephen J. Fairweather
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
- * E-mail: (SJF); (GGvD)
| | - Esther Rajendran
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Martin Blume
- Department of Biochemistry and Molecular Biology and the Bio21 Institute of Molecular Science and Biotechnology, University of Melbourne, Parkville, Victoria, Australia
- Robert Koch Institute, Berlin, Germany
| | - Kiran Javed
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Birte Steinhöfel
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
- Humboldt University Berlin, Berlin, Germany
| | - Malcolm J. McConville
- Department of Biochemistry and Molecular Biology and the Bio21 Institute of Molecular Science and Biotechnology, University of Melbourne, Parkville, Victoria, Australia
| | - Kiaran Kirk
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Stefan Bröer
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Giel G. van Dooren
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
- * E-mail: (SJF); (GGvD)
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7
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Stasic AJ, Dykes EJ, Cordeiro CD, Vella SA, Fazli MS, Quinn S, Docampo R, Moreno SNJ. Ca 2+ entry at the plasma membrane and uptake by acidic stores is regulated by the activity of the V-H + -ATPase in Toxoplasma gondii. Mol Microbiol 2021; 115:1054-1068. [PMID: 33793004 DOI: 10.1111/mmi.14722] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 03/21/2021] [Accepted: 03/26/2021] [Indexed: 12/14/2022]
Abstract
Ca2+ is a universal intracellular signal that regulates many cellular functions. In Toxoplasma gondii, the controlled influx of extracellular and intracellular Ca2+ into the cytosol initiates a signaling cascade that promotes pathogenic processes like tissue destruction and dissemination. In this work, we studied the role of proton transport in cytosolic Ca2+ homeostasis and the initiation of Ca2+ signaling. We used a T. gondii mutant of the V-H+ -ATPase, a pump previously shown to transport protons to the extracellular medium, and to control intracellular pH and membrane potential and we show that proton gradients are important for maintaining resting cytosolic Ca2+ at physiological levels and for Ca2+ influx. Proton transport was also important for Ca2+ storage by acidic stores and, unexpectedly, the endoplasmic reticulum. Proton transport impacted the amount of polyphosphate (polyP), a phosphate polymer that binds Ca2+ and concentrates in acidocalcisomes. This was supported by the co-localization of the vacuolar transporter chaperone 4 (VTC4), the catalytic subunit of the VTC complex that synthesizes polyP, with the V-ATPase in acidocalcisomes. Our work shows that proton transport regulates plasma membrane Ca2+ transport and control acidocalcisome polyP and Ca2+ content, impacting Ca2+ signaling and downstream stimulation of motility and egress in T. gondii.
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Affiliation(s)
- Andrew J Stasic
- Center for Tropical and Emerging Global Diseases, University of Georgia, Georgia, GA, USA
| | - Eric J Dykes
- Center for Tropical and Emerging Global Diseases, University of Georgia, Georgia, GA, USA.,Department of Cellular Biology, University of Georgia, Athens, GA, USA
| | - Ciro D Cordeiro
- Center for Tropical and Emerging Global Diseases, University of Georgia, Georgia, GA, USA.,Department of Cellular Biology, University of Georgia, Athens, GA, USA
| | - Stephen A Vella
- Center for Tropical and Emerging Global Diseases, University of Georgia, Georgia, GA, USA
| | - Mojtaba S Fazli
- Department of Computer Sciences, University of Georgia, Athens, GA, USA
| | - Shannon Quinn
- Department of Cellular Biology, University of Georgia, Athens, GA, USA.,Department of Computer Sciences, University of Georgia, Athens, GA, USA
| | - Roberto Docampo
- Center for Tropical and Emerging Global Diseases, University of Georgia, Georgia, GA, USA.,Department of Cellular Biology, University of Georgia, Athens, GA, USA
| | - Silvia N J Moreno
- Center for Tropical and Emerging Global Diseases, University of Georgia, Georgia, GA, USA.,Department of Cellular Biology, University of Georgia, Athens, GA, USA
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8
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Identifying the major lactate transporter of Toxoplasma gondii tachyzoites. Sci Rep 2021; 11:6787. [PMID: 33762657 PMCID: PMC7991638 DOI: 10.1038/s41598-021-86204-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 03/10/2021] [Indexed: 11/09/2022] Open
Abstract
Toxoplasma gondii and Plasmodium falciparum parasites both extrude l-lactate, a byproduct of glycolysis. The P. falciparum Formate Nitrite Transporter, PfFNT, mediates l-lactate transport across the plasma membrane of P. falciparum parasites and has been validated as a drug target. The T. gondii genome encodes three FNTs that have been shown to transport l-lactate, and which are proposed to be the targets of several inhibitors of T. gondii proliferation. Here, we show that each of the TgFNTs localize to the T. gondii plasma membrane and are capable of transporting l-lactate across it, with TgFNT1 making the primary contribution to l-lactate transport during the disease-causing lytic cycle of the parasite. We use the Xenopus oocyte expression system to provide direct measurements of l-lactate transport via TgFNT1. We undertake a genetic analysis of the importance of the tgfnt genes for parasite proliferation, and demonstrate that all three tgfnt genes can be disrupted individually and together without affecting the lytic cycle under in vitro culture conditions. Together, our experiments identify the major lactate transporter in the disease causing stage of T. gondii, and reveal that this transporter is not required for parasite proliferation, indicating that TgFNTs are unlikely to be targets for anti-Toxoplasma drugs.
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9
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Asady B, Dick CF, Ehrenman K, Sahu T, Romano JD, Coppens I. A single Na+-Pi cotransporter in Toxoplasma plays key roles in phosphate import and control of parasite osmoregulation. PLoS Pathog 2021; 16:e1009067. [PMID: 33383579 PMCID: PMC7817038 DOI: 10.1371/journal.ppat.1009067] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Revised: 01/20/2021] [Accepted: 10/14/2020] [Indexed: 11/22/2022] Open
Abstract
Inorganic ions such as phosphate, are essential nutrients required for a broad spectrum of cellular functions and regulation. During infection, pathogens must obtain inorganic phosphate (Pi) from the host. Despite the essentiality of phosphate for all forms of life, how the intracellular parasite Toxoplasma gondii acquires Pi from the host cell is still unknown. In this study, we demonstrated that Toxoplasma actively internalizes exogenous Pi by exploiting a gradient of Na+ ions to drive Pi uptake across the plasma membrane. The Na+-dependent phosphate transport mechanism is electrogenic and functionally coupled to a cipargarmin sensitive Na+-H+-ATPase. Toxoplasma expresses one transmembrane Pi transporter harboring PHO4 binding domains that typify the PiT Family. This transporter named TgPiT, localizes to the plasma membrane, the inward buds of the endosomal organelles termed VAC, and many cytoplasmic vesicles. Upon Pi limitation in the medium, TgPiT is more abundant at the plasma membrane. We genetically ablated the PiT gene, and ΔTgPiT parasites are impaired in importing Pi and synthesizing polyphosphates. Interestingly, ΔTgPiT parasites accumulate 4-times more acidocalcisomes, storage organelles for phosphate molecules, as compared to parental parasites. In addition, these mutants have a reduced cell volume, enlarged VAC organelles, defects in calcium storage and a slightly alkaline pH. Overall, these mutants exhibit severe growth defects and have reduced acute virulence in mice. In survival mode, ΔTgPiT parasites upregulate several genes, including those encoding enzymes that cleave or transfer phosphate groups from phosphometabolites, transporters and ions exchangers localized to VAC or acidocalcisomes. Taken together, these findings point to a critical role of TgPiT for Pi supply for Toxoplasma and also for protection against osmotic stresses. Inorganic phosphate (Pi) is indispensable for the biosynthesis of key cellular components, and is involved in many metabolic and signaling pathways. Transport across the plasma membrane is the first step in the utilization of Pi. The import mechanism of Pi by the intracellular parasite Toxoplasma is unknown. We characterized a transmembrane, high-affinity Na+-Pi cotransporter, named TgPiT, expressed by the parasite at the plasma membrane for Pi uptake. Interestingly, TgPiT is also localized to inward buds of the endosomal VAC organelles and some cytoplasmic vesicles. Loss of TgPiT results in a severe reduction in Pi internalization and polyphosphate levels, but stimulation of the biogenesis of phosphate-enriched acidocalcisomes. ΔTgPiT parasites have a shrunken cell body, enlarged VAC organelles, poor release of stored calcium and a mildly alkaline pH, suggesting a role for TgPiT in the maintenance of overall ionic homeostasis. ΔTgPiT parasites are poorly infectious in vitro and in mice. The mutant appears to partially cope with the absence of TgPiT by up-regulating genes coding for ion transporters and enzymes catalyzing phosphate group transfer. Our data highlight a scenario in which the role of TgPiT in Pi and Na+ transport is functionally coupled with osmoregulation activities central to sustain Toxoplasma survival.
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Affiliation(s)
- Beejan Asady
- Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore Maryland, United States of America
| | - Claudia F. Dick
- Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore Maryland, United States of America
| | - Karen Ehrenman
- Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore Maryland, United States of America
| | - Tejram Sahu
- Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore Maryland, United States of America
| | - Julia D. Romano
- Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore Maryland, United States of America
| | - Isabelle Coppens
- Department of Molecular Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore Maryland, United States of America
- * E-mail:
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10
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Schotthöfer SK, Bohrmann J. Analysing bioelectrical phenomena in the Drosophila ovary with genetic tools: tissue-specific expression of sensors for membrane potential and intracellular pH, and RNAi-knockdown of mechanisms involved in ion exchange. BMC DEVELOPMENTAL BIOLOGY 2020; 20:15. [PMID: 32635900 PMCID: PMC7341674 DOI: 10.1186/s12861-020-00220-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 06/10/2020] [Indexed: 01/16/2023]
Abstract
Background Changes in transcellular bioelectrical patterns are known to play important roles during developmental and regenerative processes. The Drosophila follicular epithelium has proven to be an appropriate model system for studying the mechanisms by which bioelectrical signals emerge and act. Fluorescent indicator dyes in combination with various inhibitors of ion-transport mechanisms have been used to investigate the generation of membrane potentials (Vmem) and intracellular pH (pHi). Both parameters as well as their anteroposterior and dorsoventral gradients were affected by the inhibitors which, in addition, led to alterations of microfilament and microtubule patterns equivalent to those observed during follicle-cell differentiation. Results We expressed two genetically-encoded fluorescent sensors for Vmem and pHi, ArcLight and pHluorin-Moesin, in the follicular epithelium of Drosophila. By means of the respective inhibitors, we obtained comparable effects on Vmem and/or pHi as previously described for Vmem- and pHi-sensitive fluorescent dyes. In a RNAi-knockdown screen, five genes of ion-transport mechanisms and gap-junction subunits were identified exerting influence on ovary development and/or oogenesis. Loss of ovaries or small ovaries were the results of soma knockdowns of the innexins inx1 and inx3, and of the DEG/ENaC family member ripped pocket (rpk). Germline knockdown of rpk also resulted in smaller ovaries. Soma knockdown of the V-ATPase-subunit vha55 caused size-reduced ovaries with degenerating follicles from stage 10A onward. In addition, soma knockdown of the open rectifier K+channel 1 (ork1) resulted in a characteristic round-egg phenotype with altered microfilament and microtubule organisation in the follicular epithelium. Conclusions The genetic tool box of Drosophila provides means for a refined and extended analysis of bioelectrical phenomena. Tissue-specifically expressed Vmem- and pHi-sensors exhibit some practical advantages compared to fluorescent indicator dyes. Their use confirms that the ion-transport mechanisms targeted by inhibitors play important roles in the generation of bioelectrical signals. Moreover, modulation of bioelectrical signals via RNAi-knockdown of genes coding for ion-transport mechanisms and gap-junction subunits exerts influence on crucial processes during ovary development and results in cytoskeletal changes and altered follicle shape. Thus, further evidence amounts for bioelectrical regulation of developmental processes via the control of both signalling pathways and cytoskeletal organisation.
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Affiliation(s)
- Susanne Katharina Schotthöfer
- RWTH Aachen University, Institut für Biologie II, Abt. Zoologie und Humanbiologie, Worringerweg 3, 52056, Aachen, Germany
| | - Johannes Bohrmann
- RWTH Aachen University, Institut für Biologie II, Abt. Zoologie und Humanbiologie, Worringerweg 3, 52056, Aachen, Germany.
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11
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Stasic AJ, Chasen NM, Dykes EJ, Vella SA, Asady B, Starai VJ, Moreno SNJ. The Toxoplasma Vacuolar H +-ATPase Regulates Intracellular pH and Impacts the Maturation of Essential Secretory Proteins. Cell Rep 2020; 27:2132-2146.e7. [PMID: 31091451 PMCID: PMC6760873 DOI: 10.1016/j.celrep.2019.04.038] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 10/31/2018] [Accepted: 04/05/2019] [Indexed: 12/20/2022] Open
Abstract
Vacuolar-proton ATPases (V-ATPases) are conserved complexes that couple the hydrolysis of ATP to the pumping of protons across membranes. V-ATPases are known to play diverse roles in cellular physiology. We studied the Toxoplasma gondii V-ATPase complex and discovered a dual role of the pump in protecting parasites against ionic stress and in the maturation of secretory proteins in endosomal-like compartments. Toxoplasma V-ATPase subunits localize to the plasma membrane and to acidic vesicles, and characterization of conditional mutants of the a1 subunit highlighted the functionality of the complex at both locations. Microneme and rhoptry proteins are required for invasion and modulation of host cells, and they traffic via endosome-like compartments in which proteolytic maturation occurs. We show that the V-ATPase supports the maturation of rhoptry and microneme proteins, and their maturases, during their traffic to their corresponding organelles. This work underscores a role for V-ATPases in regulating virulence pathways. Stasic et al. characterize the function of the vacuolar proton ATPase in the life cycle of Toxoplasma gondii, a widespread parasite that infects almost one-third of the world’s population. The work presents molecular evidence of the pump’s role in the synthesis of virulence factors of a highly successful pathogen.
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Affiliation(s)
- Andrew J Stasic
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602-7400, USA; Department of Microbiology, University of Georgia, Athens, GA 30602-7400, USA
| | - Nathan M Chasen
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602-7400, USA; Department of Infectious Diseases, University of Georgia, Athens, GA 30602-7400, USA
| | - Eric J Dykes
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602-7400, USA
| | - Stephen A Vella
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602-7400, USA; Department of Microbiology, University of Georgia, Athens, GA 30602-7400, USA
| | - Beejan Asady
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602-7400, USA
| | - Vincent J Starai
- Department of Microbiology, University of Georgia, Athens, GA 30602-7400, USA; Department of Infectious Diseases, University of Georgia, Athens, GA 30602-7400, USA
| | - Silvia N J Moreno
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602-7400, USA; Department of Cellular Biology, University of Georgia, Athens, GA 30602-7400, USA.
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12
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Lehane AM, Dennis ASM, Bray KO, Li D, Rajendran E, McCoy JM, McArthur HM, Winterberg M, Rahimi F, Tonkin CJ, Kirk K, van Dooren GG. Characterization of the ATP4 ion pump in Toxoplasma gondii. J Biol Chem 2019; 294:5720-5734. [PMID: 30723156 DOI: 10.1074/jbc.ra118.006706] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Revised: 01/31/2019] [Indexed: 12/22/2022] Open
Abstract
The Plasmodium falciparum ATPase PfATP4 is the target of a diverse range of antimalarial compounds, including the clinical drug candidate cipargamin. PfATP4 was originally annotated as a Ca2+ transporter, but recent evidence suggests that it is a Na+ efflux pump, extruding Na+ in exchange for H+ Here we demonstrate that ATP4 proteins belong to a clade of P-type ATPases that are restricted to apicomplexans and their closest relatives. We employed a variety of genetic and physiological approaches to investigate the ATP4 protein of the apicomplexan Toxoplasma gondii, TgATP4. We show that TgATP4 is a plasma membrane protein. Knockdown of TgATP4 had no effect on resting pH or Ca2+ but rendered parasites unable to regulate their cytosolic Na+ concentration ([Na+]cyt). PfATP4 inhibitors caused an increase in [Na+]cyt and a cytosolic alkalinization in WT but not TgATP4 knockdown parasites. Parasites in which TgATP4 was knocked down or disrupted exhibited a growth defect, attributable to reduced viability of extracellular parasites. Parasites in which TgATP4 had been disrupted showed reduced virulence in mice. These results provide evidence for ATP4 proteins playing a key conserved role in Na+ regulation in apicomplexan parasites.
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Affiliation(s)
- Adele M Lehane
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia,
| | - Adelaide S M Dennis
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Katherine O Bray
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Dongdi Li
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Esther Rajendran
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - James M McCoy
- the Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC 3052, Australia, and.,the Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Hillary M McArthur
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Markus Winterberg
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Farid Rahimi
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia
| | - Christopher J Tonkin
- the Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC 3052, Australia, and.,the Department of Medical Biology, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Kiaran Kirk
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia,
| | - Giel G van Dooren
- From the Research School of Biology, Australian National University, Canberra, ACT 2601, Australia,
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13
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Seidi A, Muellner-Wong LS, Rajendran E, Tjhin ET, Dagley LF, Aw VYT, Faou P, Webb AI, Tonkin CJ, van Dooren GG. Elucidating the mitochondrial proteome of Toxoplasma gondii reveals the presence of a divergent cytochrome c oxidase. eLife 2018; 7:e38131. [PMID: 30204084 PMCID: PMC6156079 DOI: 10.7554/elife.38131] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2018] [Accepted: 09/09/2018] [Indexed: 12/17/2022] Open
Abstract
The mitochondrion of apicomplexan parasites is critical for parasite survival, although the full complement of proteins that localize to this organelle has not been defined. Here we undertake two independent approaches to elucidate the mitochondrial proteome of the apicomplexan Toxoplasma gondii. We identify approximately 400 mitochondrial proteins, many of which lack homologs in the animals that these parasites infect, and most of which are important for parasite growth. We demonstrate that one such protein, termed TgApiCox25, is an important component of the parasite cytochrome c oxidase (COX) complex. We identify numerous other apicomplexan-specific components of COX, and conclude that apicomplexan COX, and apicomplexan mitochondria more generally, differ substantially in their protein composition from the hosts they infect. Our study highlights the diversity that exists in mitochondrial proteomes across the eukaryotic domain of life, and provides a foundation for defining unique aspects of mitochondrial biology in an important phylum of parasites.
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Affiliation(s)
- Azadeh Seidi
- Research School of BiologyAustralian National UniversityCanberraAustralia
| | | | - Esther Rajendran
- Research School of BiologyAustralian National UniversityCanberraAustralia
| | - Edwin T Tjhin
- Research School of BiologyAustralian National UniversityCanberraAustralia
| | - Laura F Dagley
- The Walter and Eliza Hall Institute of Medical ResearchVictoriaAustralia
- Department of Medical BiologyUniversity of MelbourneVictoriaAustralia
| | - Vincent YT Aw
- Research School of BiologyAustralian National UniversityCanberraAustralia
| | - Pierre Faou
- Department of Biochemistry and GeneticsLa Trobe Institute for Molecular Science, La Trobe UniversityVictoriaAustralia
| | - Andrew I Webb
- The Walter and Eliza Hall Institute of Medical ResearchVictoriaAustralia
- Department of Medical BiologyUniversity of MelbourneVictoriaAustralia
| | - Christopher J Tonkin
- The Walter and Eliza Hall Institute of Medical ResearchVictoriaAustralia
- Department of Medical BiologyUniversity of MelbourneVictoriaAustralia
| | - Giel G van Dooren
- Research School of BiologyAustralian National UniversityCanberraAustralia
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14
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Kissing S, Saftig P, Haas A. Vacuolar ATPase in phago(lyso)some biology. Int J Med Microbiol 2017; 308:58-67. [PMID: 28867521 DOI: 10.1016/j.ijmm.2017.08.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 07/28/2017] [Accepted: 08/23/2017] [Indexed: 12/23/2022] Open
Abstract
Many eukaryotic cells ingest extracellular particles in a process termed phagocytosis which entails the generation of a new intracellular compartment, the phagosome. Phagosomes change their composition over time and this maturation process culminates in their fusion with acidic, hydrolase-rich lysosomes. During the maturation process, degradation and, when applicable, killing of the cargo may ensue. Many of the events that are pathologically relevant depend on strong acidification of phagosomes by the 'vacuolar' ATPase (V-ATPase). This protein complex acidifies the lumen of some intracellular compartments at the expense of ATP hydrolysis. We discuss here the roles and importance of V-ATPase in intracellular trafficking, its distribution, inhibition and activities, its role in the defense against microorganisms and the counteractivities of pathogens.
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Affiliation(s)
- Sandra Kissing
- Institut für Biochemie, Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany
| | - Paul Saftig
- Institut für Biochemie, Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany.
| | - Albert Haas
- Institut für Zellbiologie, Friedrich-Wilhelms-Universität Bonn, Ulrich-Haberland-Str. 61A, D-53121 Bonn, Germany.
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15
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Ramos CL, Gomes FM, Girard-Dias W, Almeida FP, Albuquerque PC, Kretschmer M, Kronstad JW, Frases S, de Souza W, Rodrigues ML, Miranda K. Phosphorus-rich structures and capsular architecture in Cryptococcus neoformans. Future Microbiol 2017; 12:227-238. [PMID: 28262043 DOI: 10.2217/fmb-2017-0060] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
AIM In this study, we aimed to analyze the relationship of phosphorus-rich structures with surface architecture in Cryptococcus neoformans. METHODS Phosphorus-rich structures in C. neoformans were analyzed by combining fluorescence microscopy, biochemical extraction, scanning electron microscopy, electron probe x-ray microanalysis and 3D reconstruction of high pressure frozen and freeze substituted cells by focused ion beam-scanning electron microscopy (FIB-SEM). RESULTS & CONCLUSION Intracellular and surface phosphorus-enriched structures were identified. These molecules were required for capsule assembly, as demonstrated in experiments using polysaccharide incorporation by capsule-deficient cells and mutants with defects in polyphosphate synthesis. The demonstration of intracellular and cell wall-associated polyphosphates in C. neoformans may lead to future studies involving their participation in both physiologic and pathogenic events.
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Affiliation(s)
- Caroline L Ramos
- Instituto de Microbiologia Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Fabio M Gomes
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Wendell Girard-Dias
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil
| | - Fernando P Almeida
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Priscila C Albuquerque
- Instituto de Microbiologia Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Centro de Desenvolvimento Tecnológico em Saúde (CDTS), Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
| | - Matthias Kretschmer
- Michael Smith Laboratories, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - James W Kronstad
- Michael Smith Laboratories, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.,Department of Microbiology & Immunology, University of British Columbia, Vancouver, BC, Canada
| | - Susana Frases
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Wanderley de Souza
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Marcio L Rodrigues
- Instituto de Microbiologia Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Centro de Desenvolvimento Tecnológico em Saúde (CDTS), Fundação Oswaldo Cruz, Rio de Janeiro, Brazil
| | - Kildare Miranda
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.,Instituto Nacional de Biologia Estrutural e Bioimagem, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
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16
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Kulshrestha A, Katara GK, Ginter J, Pamarthy S, Ibrahim SA, Jaiswal MK, Sandulescu C, Periakaruppan R, Dolan J, Gilman-Sachs A, Beaman KD. Selective inhibition of tumor cell associated Vacuolar-ATPase 'a2' isoform overcomes cisplatin resistance in ovarian cancer cells. Mol Oncol 2016; 10:789-805. [PMID: 26899534 DOI: 10.1016/j.molonc.2016.01.003] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 01/07/2016] [Accepted: 01/09/2016] [Indexed: 12/31/2022] Open
Abstract
Development of resistance to platinum compounds significantly hinders successful ovarian cancer (OVCA) treatment. In tumor cells, dysregulated pH gradient across cell membranes is a key physiological mechanism of metastasis/chemo-resistance. These pH alterations are mediated by aberrant activation of key multi-subunit proton pumps, Vacuolar-ATPases (V-ATPases). In tumor cells, its 'a2' isoform (V-ATPase-V0a2) is a component of functional plasma-membrane complex and promotes tumor invasion through tumor-acidification and immuno-modulation. Its involvement in chemo-resistance has not been studied. Here, we show that V-ATPase-V0a2 is over-expressed in acquired-cisplatin resistant OVCA cells (cis-A2780/cis-TOV112D). Of all the 'a' subunit isoforms, V-ATPase-V0a2 exhibited an elevated expression on plasma membrane of cisplatin-resistant cells compared to sensitive counterparts. Immuno-histochemistry revealed V-ATPase-V0a2 expression in both low grade (highly drug-resistant) and high grade (highly recurrent) human OVCA tissues indicating its role in a centralized mechanism of tumor resistance. In cisplatin resistant cells, shRNA mediated inhibition of V-ATPase-V0a2 enhanced sensitivity towards both cisplatin and carboplatin. This improved cytotoxicity was mediated by enhanced cisplatin-DNA-adduct formation and suppressed DNA-repair pathway, leading to enhanced apoptosis. Suppression of V0a2 activity strongly reduced cytosolic pH in resistant tumor cells, which is known to enhance platinum-associated DNA-damage. As an indicator of reduced metastasis and chemo-resistance, in contrast to plasma membrane localization, a diffused cytoplasmic localization of acidic vacuoles was observed in V0a2-knockdown resistant cells. Interestingly, pre-treatment with monoclonal V0a2-inhibitory antibody enhanced cisplatin cytotoxicity in resistant cells. Taken together, our findings suggest that the isoform specific inhibition of V-ATPase-V0a2 could serve as a therapeutic strategy for chemo-resistant ovarian carcinoma and improve efficacy of platinum drugs.
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Affiliation(s)
- Arpita Kulshrestha
- Department of Microbiology and Immunology, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
| | - Gajendra K Katara
- Department of Microbiology and Immunology, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
| | - Jordyn Ginter
- Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
| | - Sahithi Pamarthy
- Department of Microbiology and Immunology, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
| | - Safaa A Ibrahim
- Department of Microbiology and Immunology, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
| | - Mukesh K Jaiswal
- Department of Microbiology and Immunology, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
| | - Corina Sandulescu
- Department of Obstetrics & Gynecology, Advocate Lutheran General Hospital, Park Ridge, IL, USA
| | - Ramayee Periakaruppan
- Department of Obstetrics & Gynecology, Advocate Lutheran General Hospital, Park Ridge, IL, USA
| | - James Dolan
- Department of Obstetrics & Gynecology, Advocate Lutheran General Hospital, Park Ridge, IL, USA
| | - Alice Gilman-Sachs
- Department of Microbiology and Immunology, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA
| | - Kenneth D Beaman
- Department of Microbiology and Immunology, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA.
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17
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Borges-Pereira L, Budu A, McKnight CA, Moore CA, Vella SA, Hortua Triana MA, Liu J, Garcia CRS, Pace DA, Moreno SNJ. Calcium Signaling throughout the Toxoplasma gondii Lytic Cycle: A STUDY USING GENETICALLY ENCODED CALCIUM INDICATORS. J Biol Chem 2015; 290:26914-26926. [PMID: 26374900 DOI: 10.1074/jbc.m115.652511] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Indexed: 11/06/2022] Open
Abstract
Toxoplasma gondii is an obligate intracellular parasite that invades host cells, creating a parasitophorous vacuole where it communicates with the host cell cytosol through the parasitophorous vacuole membrane. The lytic cycle of the parasite starts with its exit from the host cell followed by gliding motility, conoid extrusion, attachment, and invasion of another host cell. Here, we report that Ca(2+) oscillations occur in the cytosol of the parasite during egress, gliding, and invasion, which are critical steps of the lytic cycle. Extracellular Ca(2+) enhances each one of these processes. We used tachyzoite clonal lines expressing genetically encoded calcium indicators combined with host cells expressing transiently expressed calcium indicators of different colors, and we measured Ca(2+) changes in both parasites and host simultaneously during egress. We demonstrated a link between cytosolic Ca(2+) oscillations in the host and in the parasite. Our approach also allowed us to measure two new features of motile parasites, which were enhanced by Ca(2+) influx. This is the first study showing, in real time, Ca(2+) signals preceding egress and their direct link with motility, an essential virulence trait.
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Affiliation(s)
- Lucas Borges-Pereira
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602
| | - Alexandre Budu
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602
| | - Ciara A McKnight
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602
| | - Christina A Moore
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602; Department of Cellular Biology, University of Georgia, Athens, Georgia 30602
| | - Stephen A Vella
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602
| | - Miryam A Hortua Triana
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602
| | - Jing Liu
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602
| | - Celia R S Garcia
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602
| | - Douglas A Pace
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602
| | - Silvia N J Moreno
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, Georgia 30602; Department of Cellular Biology, University of Georgia, Athens, Georgia 30602.
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18
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Morin-Adeline V, Fraser ST, Stack C, Šlapeta J. Host origin determines pH tolerance of Tritrichomonas foetus isolates from the feline gastrointestinal and bovine urogenital tracts. Exp Parasitol 2015; 157:68-77. [PMID: 26160677 DOI: 10.1016/j.exppara.2015.06.017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Revised: 06/02/2015] [Accepted: 06/30/2015] [Indexed: 02/02/2023]
Abstract
The ability for protozoan parasites to tolerate pH fluctuations within their niche is critical for the establishment of infection and require the parasite to be capable of adapting to a distinct pH range. We used two host adapted Tritrichomonas foetus isolates, capable of infecting either the digestive tract (pH 5.3-6.6) of feline hosts or the reproductive tract (pH 7.4-7.8) of bovine hosts to address their adaptability to changing pH. Using flow cytometry, we investigated the pH tolerance of the bovine and feline T. foetus isolates over a range of physiologically relevant pH in vitro. Following exposure to mild acid stress (pH 6), the bovine T. foetus isolates showed a significant decrease in cell viability and increased cytoplasmic granularity (p-value < 0.003, p-value < 0.0002) compared to pH 7 and 8 (p-value > 0.7). In contrast, the feline genotype displayed an enhanced capacity to maintain cell morphology and viability (p-value > 0.05). Microscopic assessment revealed that following exposure to a weak acidic stress (pH 6), the bovine T. foetus transformed into rounded parasites with extended cell volumes and displays a decrease in viability. The higher tolerance for acidic extracellular environment of the feline isolate compared to the bovine isolate suggests that pH could be a critical factor in regulating T. foetus infections and host-specificity.
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Affiliation(s)
| | - Stuart T Fraser
- Disciplines of Physiology, Anatomy & Histology, School of Medical Sciences, University of Sydney, NSW, Australia
| | - Colin Stack
- School of Science and Health, University of Western Sydney, NSW, Australia
| | - Jan Šlapeta
- Faculty of Veterinary Science, University of Sydney, NSW, Australia.
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19
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Liu J, Pace D, Dou Z, King TP, Guidot D, Li ZH, Carruthers VB, Moreno SNJ. A vacuolar-H(+) -pyrophosphatase (TgVP1) is required for microneme secretion, host cell invasion, and extracellular survival of Toxoplasma gondii. Mol Microbiol 2014; 93:698-712. [PMID: 24975633 DOI: 10.1111/mmi.12685] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/19/2014] [Indexed: 01/17/2023]
Abstract
The vacuolar proton pyrophosphatase (H(+) -PPase) of Toxoplasma gondii (TgVP1), a membrane proton pump, localizes to acidocalcisomes and a novel lysosome-like compartment termed plant-like vacuole (PLV) or vacuolar compartment (VAC). We report the characterization of a T. gondii null mutant for the TgVP1 gene. Propagation of these mutants decreased significantly because of deficient attachment and invasion of host cells, which correlated with deficient microneme secretion. Processing of cathepsin L (CPL) in these mutants was deficient only when the parasites were incubated in the presence of low concentrations of the vacuolar H(+) -ATPase (V-H(+) -ATPase) inhibitor bafilomycin A1 , suggesting that either TgVP1 or the T. gondii V-H(+) -ATPase (TgVATPase) are sufficient to support CPL processing. The lack of TgVP1 did not affect processing of micronemal proteins, indicating that it does not contribute to proMIC maturations. The TgVP1 null mutants were more sensitive to extracellular conditions and were less virulent in mice. We demonstrate that T. gondii tachyzoites possess regulatory volume decrease capability during hypo-osmotic stress and this ability is impaired in TgVP1 null mutants implicating TgVP1 in osmoregulation. We hypothesize that osmoregulation is needed for host cell invasion and that TgVP1 plays a role during the normal lytic cycle of T. gondii.
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Affiliation(s)
- Jing Liu
- Center for Tropical and Emerging Global Diseases and Department of Cellular Biology, University of Georgia, GA, 30602-7400, USA; College of Veterinary Medicine, China Agricultural University, Beijing, 100193, China
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20
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Characterization of the chloroquine resistance transporter homologue in Toxoplasma gondii. EUKARYOTIC CELL 2014; 13:1360-70. [PMID: 24859994 DOI: 10.1128/ec.00027-14] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Mutations in the Plasmodium falciparum chloroquine resistance transporter (PfCRT) protein confer resistance to the antimalarial drug chloroquine. PfCRT localizes to the parasite digestive vacuole, the site of chloroquine action, where it mediates resistance by transporting chloroquine out of the digestive vacuole. PfCRT belongs to a family of transporter proteins called the chloroquine resistance transporter family. CRT family proteins are found throughout the Apicomplexa, in some protists, and in plants. Despite the importance of PfCRT in drug resistance, little is known about the evolution or native function of CRT proteins. The apicomplexan parasite Toxoplasma gondii contains one CRT family protein. We demonstrate that T. gondii CRT (TgCRT) colocalizes with markers for the vacuolar (VAC) compartment in these parasites. The TgCRT-containing VAC is a highly dynamic organelle, changing its morphology and protein composition between intracellular and extracellular forms of the parasite. Regulated knockdown of TgCRT expression resulted in modest reduction in parasite fitness and swelling of the VAC, indicating that TgCRT contributes to parasite growth and VAC physiology. Together, our findings provide new information on the role of CRT family proteins in apicomplexan parasites.
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21
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Comparison of protein expression profiles between three Perkinsus spp., protozoan parasites of molluscs, through 2D electrophoresis and mass spectrometry. J Invertebr Pathol 2014; 118:47-58. [DOI: 10.1016/j.jip.2014.02.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 02/19/2014] [Accepted: 02/24/2014] [Indexed: 11/24/2022]
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22
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Dissecting the energy metabolism in Mycoplasma pneumoniae through genome-scale metabolic modeling. Mol Syst Biol 2013; 9:653. [PMID: 23549481 PMCID: PMC3658275 DOI: 10.1038/msb.2013.6] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Accepted: 02/20/2013] [Indexed: 12/15/2022] Open
Abstract
A new genome-scale metabolic reconstruction of M. pneumonia is used in combination with external metabolite measurement and protein abundance measurements to quantitatively explore the energy metabolism of this genome-reduce human pathogen. ![]()
We established a detailed biomass composition for M. pneumoniae, thus allowing for growth simulations. Using our metabolic model, we corrected the metabolic network topology and the functional annotation of key metabolic enzymes. M. pneumoniae, unlike other laboratory-grown bacteria, uses a high fraction of energy (up to 89%) for cellular maintenance and not for growth. Simulating different growth conditions as well as single and double mutant phenotypes, we analyzed pathway connectivity and the impact of gene deletions on the growth performance of M. pneumoniae, highlighting the limited adaptive capabilities of this minimal model organism.
Mycoplasma pneumoniae, a threatening pathogen with a minimal genome, is a model organism for bacterial systems biology for which substantial experimental information is available. With the goal of understanding the complex interactions underlying its metabolism, we analyzed and characterized the metabolic network of M. pneumoniae in great detail, integrating data from different omics analyses under a range of conditions into a constraint-based model backbone. Iterating model predictions, hypothesis generation, experimental testing, and model refinement, we accurately curated the network and quantitatively explored the energy metabolism. In contrast to other bacteria, M. pneumoniae uses most of its energy for maintenance tasks instead of growth. We show that in highly linear networks the prediction of flux distributions for different growth times allows analysis of time-dependent changes, albeit using a static model. By performing an in silico knock-out study as well as analyzing flux distributions in single and double mutant phenotypes, we demonstrated that the model accurately represents the metabolism of M. pneumoniae. The experimentally validated model provides a solid basis for understanding its metabolic regulatory mechanisms.
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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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Pace DA, Fang J, Cintron R, Docampo MD, Moreno SNJ. Overexpression of a cytosolic pyrophosphatase (TgPPase) reveals a regulatory role of PP(i) in glycolysis for Toxoplasma gondii. Biochem J 2011; 440:229-40. [PMID: 21831041 PMCID: PMC4874478 DOI: 10.1042/bj20110641] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
PP(i) is a critical element of cellular metabolism as both an energy donor and as an allosteric regulator of several metabolic pathways. The apicomplexan parasite Toxoplasma gondii uses PP(i) in place of ATP as an energy donor in at least two reactions: the glycolytic PP(i)-dependent PFK (phosphofructokinase) and V-H(+)-PPase [vacuolar H(+)-translocating PPase (pyrophosphatase)]. In the present study, we report the cloning, expression and characterization of cytosolic TgPPase (T. gondii soluble PPase). Amino acid sequence alignment and phylogenetic analysis indicates that the gene encodes a family I soluble PPase. Overexpression of the enzyme in extracellular tachyzoites led to a 6-fold decrease in the cytosolic concentration of PP(i) relative to wild-type strain RH tachyzoites. Unexpectedly, this subsequent reduction in PP(i) was associated with a higher glycolytic flux in the overexpressing mutants, as evidenced by higher rates of proton and lactate extrusion. In addition to elevated glycolytic flux, TgPPase-overexpressing tachyzoites also possessed higher ATP concentrations relative to wild-type RH parasites. These results implicate PP(i) as having a significant regulatory role in glycolysis and, potentially, other downstream processes that regulate growth and cell division.
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Affiliation(s)
- Douglas A Pace
- Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602, USA.
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Miranda K, Pace DA, Cintron R, Rodrigues JCF, Fang J, Smith A, Rohloff P, Coelho E, de Haas F, de Souza W, Coppens I, Sibley LD, Moreno SNJ. Characterization of a novel organelle in Toxoplasma gondii with similar composition and function to the plant vacuole. Mol Microbiol 2010; 76:1358-75. [PMID: 20398214 DOI: 10.1111/j.1365-2958.2010.07165.x] [Citation(s) in RCA: 125] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Toxoplasma gondii belongs to the phylum Apicomplexa and is an important cause of congenital disease and infection in immunocompromised patients. Like most apicomplexans, T. gondii possesses several plant-like features, such as the chloroplast-like organelle, the apicoplast. We describe and characterize a novel organelle in T. gondii tachyzoites, which is visible by light microscopy and possesses a broad similarity to the plant vacuole. Electron tomography shows the interaction of this vacuole with other organelles. The presence of a plant-like vacuolar proton pyrophosphatase (TgVP1), a vacuolar proton ATPase, a cathepsin L-like protease (TgCPL), an aquaporin (TgAQP1), as well as Ca(2+)/H(+) and Na(+)/H(+) exchange activities, supports similarity to the plant vacuole. Biochemical characterization of TgVP1 in enriched fractions shows a functional similarity to the respective plant enzyme. The organelle is a Ca(2+) store and appears to have protective effects against salt stress potentially linked to its sodium transport activity. In intracellular parasites, the organelle fragments, with some markers colocalizing with the late endosomal marker, Rab7, suggesting its involvement with the endocytic pathway. Studies on the characterization of this novel organelle will be relevant to the identification of novel targets for chemotherapy against T. gondii and other apicomplexan parasites as well.
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Affiliation(s)
- Kildare Miranda
- Center for Tropical and Emerging Global Diseases and Department of Cellular Biology, University of Georgia, Athens, GA 30602, USA
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Abstract
Apicomplexan parasites rely on calcium-mediated signaling for a variety of vital functions including protein secretion, motility, cell invasion, and differentiation. These functions are controlled by a variety of specialized systems for uptake and release of calcium, which acts as a second messenger, and on the functions of calcium-dependent proteins. Defining these systems in parasites has been complicated by their evolutionary distance from model organisms and practical concerns in working with small, and somewhat fastidious cells. Comparative genomic analyses of Toxoplasma gondii, Plasmodium spp. and Cryptosporidium spp. reveal several interesting adaptations for calcium-related processes in parasites. Apicomplexans contain several P-type Ca2+ ATPases including an ER-type reuptake mechanism (SERCA), which is the proposed target of artemisinin. All three organisms also contain several genes related to Golgi PMR-like calcium transporters, and a Ca2+/H+ exchanger, while plasma membrane-type (PMCA) Ca2+ ATPases and voltage-dependent calcium channels are exclusively found in T. gondii. Pharmacological evidence supports the presence of IP3 and ryanodine channels for calcium-mediated release. Collectively these systems regulate calcium homeostasis and release calcium to act as a signal. Downstream responses are controlled by a family of EF-hand containing calcium binding proteins including calmodulin, and an array of centrin and caltractin-like genes. Most surprising, apicomplexans contain a diversity of calcium-dependent protein kinases (CDPK), which are commonly found in plants. Toxoplasma contains more than 20 CDPK or CDPK-like proteases, while Plasmodium and Cryptosporidium have fewer than half this number. Several of these CDPKs have been shown to play vital roles in protein secretion, invasion, and differentiation, indicating that disruption of calcium-regulated pathways may provide a novel means for selective inhibition of parasites.
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Chlorella viruses evoke a rapid release of K+ from host cells during the early phase of infection. Virology 2008; 372:340-8. [DOI: 10.1016/j.virol.2007.10.024] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2007] [Revised: 09/30/2007] [Accepted: 10/24/2007] [Indexed: 11/18/2022]
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Miranda K, de Souza W, Plattner H, Hentschel J, Kawazoe U, Fang J, Moreno SNJ. Acidocalcisomes in Apicomplexan parasites. Exp Parasitol 2008; 118:2-9. [PMID: 17761167 DOI: 10.1016/j.exppara.2007.07.009] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2007] [Revised: 07/19/2007] [Accepted: 07/21/2007] [Indexed: 10/23/2022]
Abstract
Acidocalcisomes are acidic calcium stores found in diverse organisms, being conserved from bacteria to man. They posses an acidic matrix that contains several cations bound to phosphates, mainly present in the form of short and long polyphosphate chains. Their matrix is acidified through the action of proton pumps such as a vacuolar proton ATPase and a vacuolar proton pyrophosphatase. The calcium uptake occurs through a Ca2+/H+ counter transporting ATPase located in the membrane of the organelle. Acidocalcisomes have been identified in a variety of microorganisms, including Apicomplexan parasites such as Plasmodium and Eimeria species, and in Toxoplasma gondii. In this paper, we review the structural, biochemical and physiological aspects of acidocalcisomes in Apicomplexan parasites and discuss their functional roles in the maintenance of intracellular ion homeostasis.
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Affiliation(s)
- Kildare Miranda
- Center for Tropical and Emerging Global Diseases and Department of Cellular Biology, 350 Paul D. Coverdell Center, University of Georgia, Athens, GA 30602, USA
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Marchesini N, Vieira M, Luo S, Moreno SNJ, Docampo R. A Malaria Parasite-encoded Vacuolar H+-ATPase Is Targeted to the Host Erythrocyte. J Biol Chem 2005; 280:36841-7. [PMID: 16135514 DOI: 10.1074/jbc.m507727200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The asexual development of malaria parasites inside the erythrocyte is accompanied by changes in the composition, structure, and function of the host cell membrane and cytoplasm. The parasite exports a membrane network into the host cytoplasm and several proteins that are inserted into the erythrocyte membrane, although none of these proteins has been shown to have enzymatic activity. We report here that a functional malaria parasite-encoded vacuolar (V)-H(+)-ATPase is exported to the erythrocyte and localized in membranous structures and in the plasma membrane of the infected erythrocyte. This localization was determined by separation of parasite and erythrocyte membranes and determination of enzyme marker activities and by immunofluorescence microscopy assays using antibodies against the B subunit of the malarial V-H(+)-ATPase and erythrocyte (spectrins) and parasite (merozoite surface protein 1) markers. Our results suggest that this pump has a role in the maintenance of the intracellular pH (pH(i)) of the infected erythrocyte. Our results also indicate that although the pH(i) maintained by the V-H(+)-ATPase is important for maximum uptake of small metabolites at equilibrium, it does not appear to affect transport across the erythrocyte membrane and is, therefore, not involved in the previously described phenomenon of increased permeability of infected erythrocytes that is sensitive to chloride channel inhibitors (new permeation pathway). This constitutes the first report of the presence of a functional enzyme of parasite origin in the plasma membrane of its host.
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Affiliation(s)
- Norma Marchesini
- Department of Pathobiology and Center for Zoonoses Research, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802, USA
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Moraes Moreira BL, Soares Medeiros LCA, Miranda K, de Souza W, Hentschel J, Plattner H, Barrabin H. Kinetics of pyrophosphate-driven proton uptake by acidocalcisomes of Leptomonas wallacei. Biochem Biophys Res Commun 2005; 334:1206-13. [PMID: 16039991 DOI: 10.1016/j.bbrc.2005.06.205] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2005] [Accepted: 06/27/2005] [Indexed: 11/22/2022]
Abstract
In this work, we show the kinetics of pyrophosphate-driven H+ uptake by acidocalcisomes in digitonin-permeabilized promastigotes of Leptomonas wallacei. The vacuolar proton pyrophosphatase activity was optimal in the pH range of 7.5-8.0, was inhibited by imidiodiphosphate, and was completely dependent on K+ and PPi. H+ was released with the addition of Ca2+, suggesting the presence of a Ca2+/H+ antiport. In addition, X-ray elemental mapping associated with energy-filtering transmission electron microscopy showed that most of the Ca, Na, Mg, P, K, Fe, and Zn were located in acidocalcisomes. L. wallacei immunolabeled with antibodies against Trypanosoma cruzi pyrophosphatase show intense fluorescence in cytoplasmatic organelles of size and distribution similar to the acidocalcisomes. Altogether, the results show that L. wallacei acidocalcisomes possess a H+-pyrophosphatase with characteristics of type I V-H+-PPase. However, we did not find any evidence, either for the presence of H+-ATPases or for Na+/H+ exchangers in these acidocalcisomes.
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Elandalloussi LM, Adams B, Smith PJ. ATPase activity of purified plasma membranes and digestive vacuoles from Plasmodium falciparum. Mol Biochem Parasitol 2005; 141:49-56. [PMID: 15811526 DOI: 10.1016/j.molbiopara.2005.02.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2004] [Revised: 01/31/2005] [Accepted: 02/03/2005] [Indexed: 11/21/2022]
Abstract
The ATPase activity of the human malaria parasite, Plasmodium falciparum was investigated using two experimental systems, (i) digestive vacuoles, and (ii) purified plasma membranes isolated from a chloroquine-sensitive and a chloroquine-resistant strain. No correlation between the level of ATPase activity and chloroquine sensitivity could be detected. In both systems, the ATPase activity of the chloroquine-resistant and -sensitive strain was decreased in the presence of the P-glycoprotein inhibitor vanadate. Susceptibility to inhibition by vanadate together with the lack of effect of ouabain implies a P-type ATPase activity in the plasma membrane. Furthermore, the inhibition of Fac8 ATPase activity by oligomycin both in the digestive vacuoles and the plasma membranes would be consistent with higher levels of Pgh1 in Fac8. Our data are consistent with the presence of a V-type H+-ATPase in the parasite food vacuole. Bafilomycin A1 and N-ethylmaleimide decreased the vacuolar ATPase activity in both chloroquine-resistant and -sensitive strains. Interestingly, a 30% decrease was observed between the ATPase activity of plasma membranes isolated from Fac8 and D10 in the presence of bafilomycin A1, suggesting the presence of a V-type ATPase in D10 plasma membrane that is underexpressed or altered in the plasma membrane of the chloroquine-resistant Fac8. The chemosensitisers tested had no effect on the ATPase activity of chloroquine-resistant P. falciparum in both systems suggesting that their activity is not mediated through an ATP-dependent mechanism. No effect was observed on the vacuolar ATPase activity in the presence of the antimalarials tested indicating that an ATP-dependent transport has not been activated.
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Affiliation(s)
- Laurence M Elandalloussi
- Department of Pharmacology, University of Cape Town, Medical School, Observatory 7925, South Africa
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Soares Medeiros LCA, Moreira BLM, Miranda K, de Souza W, Plattner H, Hentschel J, Barrabin H. A proton pumping pyrophosphatase in acidocalcisomes of Herpetomonas sp. Mol Biochem Parasitol 2005; 140:175-82. [PMID: 15760657 DOI: 10.1016/j.molbiopara.2004.12.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2004] [Revised: 12/27/2004] [Accepted: 12/27/2004] [Indexed: 11/30/2022]
Abstract
Acidocalcisomes are acidic calcium storage organelles found in several microorganisms. They are characterized by their acidic nature, high electron density, high content of polyphosphates and several cations. Electron microscopy contrast tuned images of Herpetomonas sp. showed the presence of several electron dense organelles ranging from 100 to 300 nm in size. In addition, X-ray element mapping associated with energy-filtering transmission electron microscopy showed that most of the cations, namely Na, Mg, P, K, Fe and Zn, are located in their matrix. Using acridine orange as an indicator dye, a pyrophosphate-driven H+ uptake was measured in cells permeabilized by digitonin. This uptake has an optimal pH of 6.5-6.7 and was inhibited by sodium fluoride (NaF) and imidodiphosphate (IDP), two H+-pyrophosphatase inhibitors. H+ uptake was not promoted by ATP. Addition of 50 microM Ca2+ induced the release of H+, suggesting the presence of a Ca2+/H+ countertransport system in the membranes of the acidic compartments. Na+ was unable to release protons from the organelles. The pyrophosphate-dependent H+ uptake was dependent of ion K+ and inhibited by Na+ Herpetomonas sp. immunolabeled with monoclonal antibodies raised against a Trypanosoma cruzi V-H+-pyrophosphatase shows intense fluorescence in cytoplasmatic organelles of size and distribution similar to the electron-dense vacuoles. Together, these results suggest that the electron dense organelles found in Herpetomonas sp. are homologous to the acidocalcisomes described in other trypanosomatids. They possess a vacuolar H+-pyrophosphatase and a Ca2+/H+ antiport. However, in contrast to the other trypanosomatids so far studied, we were not able to measure any ATP promoted H+ transport in the acidocalcisomes of this parasite.
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Affiliation(s)
- Lia Carolina A Soares Medeiros
- Departmento de Bioquímica Médica, ICB-CCS Universidade Federal do Rio de Janeiro, UFRJ Ilha do Fundão, 21941-590 Rio de Janeiro, Brazil
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Arrizabalaga G, Ruiz F, Moreno S, Boothroyd JC. Ionophore-resistant mutant of Toxoplasma gondii reveals involvement of a sodium/hydrogen exchanger in calcium regulation. ACTA ACUST UNITED AC 2004; 165:653-62. [PMID: 15173192 PMCID: PMC2172388 DOI: 10.1083/jcb.200309097] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Calcium is a critical mediator of many intracellular processes in eukaryotic cells. In the obligate intracellular parasite Toxoplasma gondii, for example, a rise in [Ca2+] is associated with significant morphological changes and rapid egress from host cells. To understand the mechanisms behind such dramatic effects, we isolated a mutant that is altered in its responses to the Ca2+ ionophore A23187 and found the affected gene encodes a homologue of Na+/H+ exchangers (NHEs) located on the parasite's plasma membrane. We show that in the absence of TgNHE1, Toxoplasma is resistant to ionophore-induced egress and extracellular death and amiloride-induced proton efflux inhibition. In addition, the mutant has increased levels of intracellular Ca2+, which explains its decreased sensitivity to A23187. These results provide direct genetic evidence of a role for NHE1 in Ca2+ homeostasis and important insight into how this ubiquitous pathogen senses and responds to changes in its environment.
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Affiliation(s)
- Gustavo Arrizabalaga
- Department of Microbiology and Immunology, Fairchild Building D305, 300 Pasteur Dr., Stanford University School of Medicine, Stanford, CA 94305-5124, USA
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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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Abstract
Cell fractionation, a methodological strategy for obtaining purified organelle preparations, has been applied successfully to parasitic protozoa by a number of investigators. Here we present and discuss the work of several groups that have obtained highly purified subcellular fractions from trypanosomatids, Apicomplexa and trichomonads, and whose work have added substantially to our knowledge of the cell biology of these parasites.
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Affiliation(s)
- Wanderley de Souza
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-900, Brasil.
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Rodrigues CO, Ruiz FA, Rohloff P, Scott DA, Moreno SNJ. Characterization of isolated acidocalcisomes from Toxoplasma gondii tachyzoites reveals a novel pool of hydrolyzable polyphosphate. J Biol Chem 2002; 277:48650-6. [PMID: 12379647 DOI: 10.1074/jbc.m208990200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Toxoplasma gondii tachyzoites were fractionated by modification of an iodixanol density gradient method previously used for acidocalcisome isolation from Trypanosoma cruzi epimastigotes. Fractions were characterized using electron microscopy, x-ray microanalysis, and enzymatic markers, and it was demonstrated that the heaviest (pellet) fraction contains electron-dense vacuoles rich in phosphorus, calcium, and magnesium, as found before for acidocalcisomes. Staining with 4',6-diamidino-2-phenylindole (DAPI) indicated that poly- phosphate (polyP) was preferentially localized in this fraction together with pyrophosphate (PP(i)). Using an enzyme-based method, millimolar levels (in terms of P(i) residues) of polyP chains of less than 50 residues long and micromolar levels in polyP chains of about 700-800 residues long were found to be preferentially localized in this fraction. The fraction also contained the pyrophosphatase and polyphosphatase activities characteristic of acidocalcisomes. Western blot analysis using antibodies against proteins from micronemes, dense granules, rhoptries, and plasma membrane showed that the acidocalcisomal fraction was not contaminated by these other organelles. T. gondii polyP levels rapidly decreased upon exposure of the parasites to a calcium ionophore (ionomycin), to an inhibitor of the V-H(+)-ATPase (bafilomycin A(1)), or to the alkalinizing agent NH(4)Cl. These changes were in parallel to an increase in intracellular Ca(2+) concentration, suggesting a close association between polyP hydrolysis and Ca(2+) release from the acidocalcisome. These results provide a useful method for the isolation and characterization of acidocalcisomes, showing that they are distinct from other previously recognized organelles present in T. gondii, and provide evidence for the role of polyP metabolism in response to cellular stress.
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Affiliation(s)
- Claudia O Rodrigues
- Laboratory of Molecular Parasitology, Department of Veterinary Pathobiology, University of Illinois at Urbana-Champaign, 61802, USA
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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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Singh U, Brewer JL, Boothroyd JC. Genetic analysis of tachyzoite to bradyzoite differentiation mutants in Toxoplasma gondii reveals a hierarchy of gene induction. Mol Microbiol 2002; 44:721-33. [PMID: 11994153 DOI: 10.1046/j.1365-2958.2002.02903.x] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Developmental switching in Toxoplasma gondii, from the virulent tachyzoite to the relatively quiescent bradyzoite stage, is responsible for disease propagation and reactivation. We have generated tachyzoite to bradyzoite differentiation (Tbd-) mutants in T. gondii and used these in combination with a cDNA microarray to identify developmental pathways in bradyzoite formation. Four independently generated Tbd- mutants were analysed and had defects in bradyzoite development in response to multiple bradyzoite-inducing conditions, a stable phenotype after in vivo passages and a markedly reduced brain cyst burden in a murine model of chronic infection. Transcriptional profiles of mutant and wild-type parasites, growing under bradyzoite conditions, revealed a hierarchy of developmentally regulated genes, including many bradyzoite-induced genes whose transcripts were reduced in all mutants. A set of non-developmentally regulated genes whose transcripts were less abundant in Tbd- mutants were also identified. These may represent genes that mediate downstream effects and/or whose expression is dependent on the same transcription factors as the bradyzoite-induced set. Using these data, we have generated a model of transcription regulation during bradyzoite development in T. gondii. Our approach shows the utility of this system as a model to study developmental biology in single-celled eukaryotes including protozoa and fungi.
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Affiliation(s)
- Upinder Singh
- D305 Fairchild Building, Department of Microbiology and Immunology, Stanford University School of Medicine, CA 94305-5124, USA
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39
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Moudy R, Manning TJ, Beckers CJ. The loss of cytoplasmic potassium upon host cell breakdown triggers egress of Toxoplasma gondii. J Biol Chem 2001; 276:41492-501. [PMID: 11526113 DOI: 10.1074/jbc.m106154200] [Citation(s) in RCA: 169] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ability of intracellular parasites to monitor the viability of their host cells is essential for their survival. The protozoan parasite Toxoplasma gondii actively invades nucleated animal cells and replicates in their cytoplasm. Two to 3 days after infection, the parasite-filled host cell breaks down and the parasites leave to initiate infection of a new cell. Parasite egress from the host cell is triggered by rupture of the host plasma membrane and the ensuing reduction in the concentration of cytoplasmic potassium. The many other changes in host cell composition do not appear be used as triggers. The reduction in the host cell [K(+)] appears to activate a phospholipase C activity in Toxoplasma that, in turn, causes an increase in cytoplasmic [Ca(2+)] in the parasite. The latter appears to be necessary and sufficient for inducing egress, as buffering of cytoplasmic Ca(2+) blocks egress and calcium ionophores circumvent the need for a reduction of host cell [K(+)] and parasite phospholipase C activation. The increase in [Ca(2+)](C) brings about egress by the activation of at least two signaling pathways: the protein kinase TgCDPK1 and the calmodulin-dependent protein phosphatase calcineurin.
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Affiliation(s)
- R Moudy
- Division of Geographic Medicine, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294-2170, USA
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40
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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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41
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Robibaro B, Hoppe HC, Yang M, Coppens I, Ngô HM, Stedman TT, Paprotka K, Joiner KA. Endocytosis in different lifestyles of protozoan parasitism: role in nutrient uptake with special reference to Toxoplasma gondii. Int J Parasitol 2001; 31:1343-53. [PMID: 11566302 DOI: 10.1016/s0020-7519(01)00252-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
A fundamental property of any eukaryotic cell is endocytosis, that is the ability to take up external fluid, solutes and particulate matter into membrane-bound intracellular vesicles by various mechanisms. Toxoplasma gondii is an intracellular protozoan parasite of the phylum Apicomplexa with a wide geographical and host range distribution. Significant progress in studying the cell biology of this parasite has been accomplished over the last few years. Only recently endocytic compartments and endocytic trafficking have come to a closer dissection in T. gondii. In this review, we discuss the evidence for an endocytic compartment and present a model for an endocytic pathway in Toxoplasma against a background of endocytosis in kinetoplastida and the extensive insights gained from mammalian and yeast cells.
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Affiliation(s)
- B Robibaro
- Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, LCI, 808333 Cedar Street, New Haven, CT 06520-8022, USA
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42
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Biagini GA, Knodler LA, Saliba KJ, Kirk K, Edwards MR. Na(+)-dependent pH regulation by the amitochondriate protozoan parasite Giardia intestinalis. J Biol Chem 2001; 276:29157-62. [PMID: 11297564 DOI: 10.1074/jbc.m102728200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Giardia intestinalis is a pathogenic fermentative parasite, which inhabits the gastrointestinal tract of animals and humans. G. intestinalis trophozoites are exposed to acidic fluctuations in vivo and must also cope with acidic metabolic endproducts. In this study, a combination of independent techniques ((31)P NMR spectroscopy, distribution of the weak acid pH marker 5,5-dimethyl-2,4-oxazolidinedione (DMO) and the fluorescent pH indicator 2',7'-bis (carboxyethyl)-5,6-carboxyfluorescein (BCECF)) were used to show that G. intestinalis trophozoites exposed to an extracellular pH range of 6.0--7.5 maintain their cytosolic pH (pH(i)) within the range 6.7--7.1. Maintenance of the resting pH(i) was Na(+)-dependent but unaffected by amiloride (or analogs thereof). Recovery of pH(i) from an intracellular acidosis was also Na(+)-dependent, with the rate of recovery varying with the extracellular Na(+) concentration in a saturable manner (K(m) = 18 mm; V(max) = 10 mm H(+) min(-1)). The recovery of pH(i) from an acid load was inhibited by amiloride but unaffected by a number of its analogs. The postulated involvement of one or more Na(+)/H(+) exchanger(s) in the regulation of pH(i) in G. intestinalis is discussed.
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Affiliation(s)
- G A Biagini
- School of Biochemistry and Molecular Genetics, University of New South Wales, Sydney 2052, Australia.
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43
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Abstract
The malaria parasite is a unicellular eukaryotic organism which, during the course of its complex life cycle, invades the red blood cells of its vertebrate host. As it grows and multiplies within its host blood cell, the parasite modifies the membrane permeability and cytosolic composition of the host cell. The intracellular parasite is enclosed within a so-called parasitophorous vacuolar membrane, tubular extensions of which radiate out into the host cell compartment. Like all eukaryote cells, the parasite has at its surface a plasma membrane, as well as having a variety of internal membrane-bound organelles that perform a range of functions. This review focuses on the transport properties of the different membranes of the malaria-infected erythrocyte, as well as on the role played by the various membrane transport systems in the uptake of solutes from the extracellular medium, the disposal of metabolic wastes, and the origin and maintenance of electrochemical ion gradients. Such systems are of considerable interest from the point of view of antimalarial chemotherapy, both as drug targets in their own right and as routes for targeting cytotoxic agents into the intracellular parasite.
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Affiliation(s)
- K Kirk
- Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, Australian Capital Territory, Australia.
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44
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Holpert M, Lüder CG, Gross U, Bohne W. Bradyzoite-specific expression of a P-type ATPase in Toxoplasma gondii. Mol Biochem Parasitol 2001; 112:293-6. [PMID: 11223136 DOI: 10.1016/s0166-6851(00)00361-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- M Holpert
- Department of Bacteriology, University of Göttingen, Kreuzbergring 57, D-37075 Göttingen, Germany
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45
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Luo S, Vieira M, Graves J, Zhong L, Moreno SN. A plasma membrane-type Ca(2+)-ATPase co-localizes with a vacuolar H(+)-pyrophosphatase to acidocalcisomes of Toxoplasma gondii. EMBO J 2001; 20:55-64. [PMID: 11226155 PMCID: PMC140201 DOI: 10.1093/emboj/20.1.55] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Ca(2+)-ATPases are likely to play critical roles in the biochemistry of Toxoplasma gondii, since these protozoa are obligate intracellular parasites and the Ca(2+) concentration in their intracellular location is three orders of magnitude lower than in the extracellular medium. Here, we report the cloning and sequencing of a gene encoding a plasma membrane-type Ca(2+)-ATPase (PMCA) of T.gondii (TgA1). The predicted protein (TgA1) exhibits 32-36% identity to vacuolar Ca(2+)-ATPases of Trypanosoma cruzi, Saccharomyces cerevisiae, Entamoeba histolytica and Dictyostelium discoideum. Sequencing of both cDNA and genomic DNA from T.gondii indicated that TgA1 contains two introns near the C-terminus. A hydropathy profile of the protein suggests 10 transmembrane domains. TgA1 suppresses the Ca(2+) hypersensitivity of a mutant of S.cerevisiae that has a defect in vacuolar Ca(2+) accumulation. Indirect immunofluorescence and immunoelectron microscopy analysis indicate that TgA1 localizes to the plasma membrane and co-localizes with the vacuolar H(+)-pyrophosphatase to intracellular vacuoles identified morphologically and by X-ray microanalysis as the acidocalcisomes. This vacuolar-type Ca(2+)-ATPase could play an important role in Ca(2+) homeostasis in T.gondii.
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Affiliation(s)
| | | | | | | | - Silvia N.J. Moreno
- Laboratory of Molecular Parasitology, Department of Pathobiology, University of Illinois at Urbana-Champaign, 2001 South Lincoln Avenue, Urbana, IL 61802, USA
Corresponding author e-mail:
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46
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Abstract
Giardia intestinalis is a primitive microaerophilic protozoan parasite which colonises the upper intestine of humans. Despite the evolutionary and medical significance of this organism, its physiology is very poorly understood. In this study we have used a novel flow cytometric technique to make quantitative measurements of the electrical potential across the plasma membrane of G. intestinalis trophozoites. In media lacking both K(+) and Na(+), G. intestinalis trophozoites maintained a high negative plasma membrane potential (Psi(m)) of -134+/-3 mV. The Psi(m) was unaffected by the addition of Na(+) to the extracellular medium, whereas the addition of K(+) resulted in a significant membrane depolarisation, consistent with the G. intestinalis trophozoite plasma membrane having a significant (electrophoretic) permeability to K(+). The membrane was also depolarised by the H(+) ionophore m-chlorophenylhydrazone and by the H(+) ATPase inhibitors dicyclohexylcarbodiimide and N-ethylmaleimide. These results are consistent with G. intestinalis trophozoites maintaining a high resting Psi(m), originating at least in part from an electrogenic H(+) pump acting in concert with a K(+) diffusion pathway.
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Affiliation(s)
- G A Biagini
- School of Biochemistry and Molecular Genetics, University of New South Wales, Sydney, NSW, Australia
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47
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de Souza W, Carreiro IP, Miranda K, Silva NL. Two special organelles found in Trypanosoma cruzi. AN ACAD BRAS CIENC 2000; 72:421-32. [PMID: 11028107 DOI: 10.1590/s0001-37652000000300016] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We review here two unique organelles from Trypanosoma cruzi. One of them is the acidocalcisome, cytoplasmic vacuoles containing a very high Ca2+ concentration and a Ca2+ - H+ translocating ATPase activity, present in all trypanosomatids. The other organelle is the reservosome, site of accumulation of endocytosed macromolecules, very rich in cysteine proteinase, that is present only in epimastigote forms of trypanosomes belonging to the Schyzotrypanum sub-genus.
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Affiliation(s)
- W de Souza
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21949-900, Brazil.
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48
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Rodrigues CO, Scott DA, Bailey BN, De Souza W, Benchimol M, Moreno B, Urbina JA, Oldfield E, Moreno SN. Vacuolar proton pyrophosphatase activity and pyrophosphate (PPi) in Toxoplasma gondii as possible chemotherapeutic targets. Biochem J 2000; 349 Pt 3:737-45. [PMID: 10903134 PMCID: PMC1221200 DOI: 10.1042/bj3490737] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The addition of PP(i) promoted the acidification of a subcellular compartment in cell homogenates of Toxoplasma gondii tachyzoites, implying the presence of a proton-translocating pyrophosphatase. The proton gradient was collapsed by addition of the K(+)/H(+) antiporter nigericin, and was also inhibited by addition of the PP(i) analogue aminomethylenediphosphonate (AMDP). Both proton transport and PP(i) hydrolysis were dependent upon K(+), but Na(+) caused partial inhibition of these activities. PP(i) hydrolysis was sensitive in a dose-dependent manner to AMDP, imidodiphosphate, NaF and to the thiol reagent N-ethylmaleimide. This activity was unaffected by common inhibitors of phosphohydrolases, except that NaO(3)V (sodium orthovanadate) stimulated the activity by 87%. Immunofluorescence microscopy, using antisera raised against conserved peptide sequences of a plant vacuolar pyrophosphatase, suggested that the pyrophosphatase in T. gondii tachyzoites was located in the plasma membrane and intracellular vacuoles of the parasite. High-field (31)P-NMR spectroscopy showed that PP(i )was more abundant than ATP in tachyzoites. Bisphosphonates (PP(i) analogues), drugs that are used in the treatment of bone diseases, inhibited proton transport and PP(i) hydrolysis in tachyzoite homogenates, and also inhibited intracellular proliferation of tachyzoites in tissue culture cells.
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Affiliation(s)
- C O Rodrigues
- Laboratory of Molecular Parasitology, Department of Pathobiology, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, 2001 South Lincoln Avenue, Urbana, IL 61802, USA
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49
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Saliba KJ, Kirk K. pH regulation in the intracellular malaria parasite, Plasmodium falciparum. H(+) extrusion via a V-type H(+)-ATPase. J Biol Chem 1999; 274:33213-9. [PMID: 10559194 DOI: 10.1074/jbc.274.47.33213] [Citation(s) in RCA: 146] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanism by which the intra-erythrocytic form of the human malaria parasite, Plasmodium falciparum, extrudes H(+) ions and thereby regulates its cytosolic pH (pH(i)), was investigated using saponin-permeabilized parasitized erythrocytes. The parasite was able both to maintain its resting pH(i) and to recover from an imposed intracellular acidification in the absence of extracellular Na(+), thus ruling out the involvement of a Na(+)/H(+) exchanger in both processes. Both phenomena were ATP-dependent. Amiloride and the related compound ethylisopropylamiloride caused a substantial reduction in the resting pH(i) of the parasite, whereas EMD 96785, a potent and allegedly selective inhibitor of Na(+)/H(+) exchange, had relatively little effect. The resting pH(i) of the parasite was also reduced by the sulfhydryl reagent N-ethylmaleimide, by the carboxyl group blocker N,N'-dicyclohexylcarbodiimide, and by bafilomycin A(1), a potent inhibitor of V-type H(+)-ATPases. Bafilomycin A(1) blocked pH(i) recovery in parasites subjected to an intracellular acidification and reduced the rate of acidification of a weakly buffered solution by parasites under resting conditions. The data are consistent with the hypothesis that the malaria parasite, like other parasitic protozoa, has in its plasma membrane a V-type H(+)-ATPase, which serves as the major route for the efflux of H(+) ions.
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Affiliation(s)
- K J Saliba
- Division of Biochemistry, Faculty of Science, Australian National University, Canberra, Australian Capital Territory 0200, Australia
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50
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Docampo R, Moreno SN. Acidocalcisome: A novel Ca2+ storage compartment in trypanosomatids and apicomplexan parasites. PARASITOLOGY TODAY (PERSONAL ED.) 1999; 15:443-8. [PMID: 10511686 DOI: 10.1016/s0169-4758(99)01531-8] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Acidocalcisomes are novel acidic Ca2+ storage organelles found in trypanosomatids and apicomplexan parasites, abundant in the intracellular stages of these parasites, and characterized by their high electron density, and high content of phosphorus, Ca2+, Mg2+, Na+ and Zn2+. A number of energy-utilizing pumps and exchangers have been found in these organelles, which underlines their importance in the homeostasis of different elements, as discussed here by Roberto Docampo and Silvia Moreno.
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Affiliation(s)
- R Docampo
- Laboratory of Molecular Parasitology, Department of Pathobiology, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, 2001 South Lincoln Avenue, Urbana, IL 61802, USA.
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