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Chmelová Ľ, Kraeva N, Saura A, Krayzel A, Vieira CS, Ferreira TN, Soares RP, Bučková B, Galan A, Horáková E, Vojtková B, Sádlová J, Malysheva MN, Butenko A, Prokopchuk G, Frolov AO, Lukeš J, Horváth A, Škodová-Sveráková I, Feder D, Yu Kostygov A, Yurchenko V. Intricate balance of dually-localized catalase modulates infectivity of Leptomonas seymouri (Kinetoplastea: Trypanosomatidae). Int J Parasitol 2024; 54:391-400. [PMID: 38663543 DOI: 10.1016/j.ijpara.2024.04.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 03/24/2024] [Accepted: 04/19/2024] [Indexed: 05/02/2024]
Abstract
Nearly all aerobic organisms are equipped with catalases, powerful enzymes scavenging hydrogen peroxide and facilitating defense against harmful reactive oxygen species. In trypanosomatids, this enzyme was not present in the common ancestor, yet it had been independently acquired by different lineages of monoxenous trypanosomatids from different bacteria at least three times. This observation posited an obvious question: why was catalase so "sought after" if many trypanosomatid groups do just fine without it? In this work, we analyzed subcellular localization and function of catalase in Leptomonas seymouri. We demonstrated that this enzyme is present in the cytoplasm and a subset of glycosomes, and that its cytoplasmic retention is H2O2-dependent. The ablation of catalase in this parasite is not detrimental in vivo, while its overexpression resulted in a substantially higher parasite load in the experimental infection of Dysdercus peruvianus. We propose that the capacity of studied flagellates to modulate the catalase activity in the midgut of its insect host facilitates their development and protects them from oxidative damage at elevated temperatures.
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Affiliation(s)
- Ľubomíra Chmelová
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia
| | - Natalya Kraeva
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia
| | - Andreu Saura
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia
| | - Adam Krayzel
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia
| | - Cecilia Stahl Vieira
- Universidade Federal Fluminense, Instituto de Biologia, Programa de Pós-Graduação em Ciências e Biotecnologia, Niterói, Brazil
| | - Tainá Neves Ferreira
- Universidade Federal Fluminense, Instituto de Biologia, Programa de Pós-Graduação em Ciências e Biotecnologia, Niterói, Brazil
| | - Rodrigo Pedro Soares
- Biotechnology Applied to Pathogens (BAP), Instituto René Rachou, Fundação Oswaldo Cruz, Belo Horizonte, Brazil
| | - Barbora Bučková
- Department of Biochemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia
| | - Arnau Galan
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia
| | - Eva Horáková
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czechia
| | - Barbora Vojtková
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czechia
| | - Jovana Sádlová
- Department of Parasitology, Faculty of Science, Charles University, Prague, Czechia
| | - Marina N Malysheva
- Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia
| | - Anzhelika Butenko
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia; Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czechia; Faculty of Science, University of South Bohemia, České Budějovice, Czechia
| | - Galina Prokopchuk
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czechia; Faculty of Science, University of South Bohemia, České Budějovice, Czechia
| | - Alexander O Frolov
- Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia
| | - Julius Lukeš
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czechia; Faculty of Science, University of South Bohemia, České Budějovice, Czechia
| | - Anton Horváth
- Department of Biochemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia
| | - Ingrid Škodová-Sveráková
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia; Department of Biochemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia; Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czechia
| | - Denise Feder
- Universidade Federal Fluminense, Instituto de Biologia, Programa de Pós-Graduação em Ciências e Biotecnologia, Niterói, Brazil; Universidade Federal Fluminense, Instituto de Biologia, Laboratório de Biologia de Insetos, Niterói, Brazil; Instituto Nacional de Entomologia Molecular, Rio de Janeiro, Brazil
| | - Alexei Yu Kostygov
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia; Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia
| | - Vyacheslav Yurchenko
- Life Science Research Centre, Faculty of Science, University of Ostrava, Ostrava, Czechia.
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Faktorová D, Záhonová K, Benz C, Dacks JB, Field MC, Lukeš J. Functional differentiation of Sec13 paralogues in the euglenozoan protists. Open Biol 2023; 13:220364. [PMID: 37311539 DOI: 10.1098/rsob.220364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Accepted: 05/23/2023] [Indexed: 06/15/2023] Open
Abstract
The β-propeller protein Sec13 plays roles in at least three distinct processes by virtue of being a component of the COPII endoplasmic reticulum export vesicle coat, the nuclear pore complex (NPC) and the Seh1-associated (SEA)/GATOR nutrient-sensing complex. This suggests that regulatory mechanisms coordinating these cellular activities may operate via Sec13. The NPC, COPII and SEA/GATOR are all ancient features of eukaryotic cells, and in the vast majority of eukaryotes, a single Sec13 gene is present. Here we report that the Euglenozoa, a lineage encompassing the diplonemid, kinetoplastid and euglenid protists, possess two Sec13 paralogues. Furthermore, based on protein interactions and localization studies we show that in diplonemids Sec13 functions are divided between the Sec13a and Sec13b paralogues. Specifically, Sec13a interacts with COPII and the NPC, while Sec13b interacts with Sec16 and components of the SEA/GATOR complex. We infer that euglenozoan Sec13a is responsible for NPC functions and canonical anterograde transport activities while Sec13b acts within nutrient and autophagy-related pathways, indicating a fundamentally distinct organization of coatomer complexes in euglenozoan flagellates.
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Affiliation(s)
- Drahomíra Faktorová
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
- Faculty of Sciences, University of South Bohemia, České Budějovice, Czech Republic
| | - Kristína Záhonová
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
- Faculty of Science, Charles University, BIOCEV, Vestec, Czech Republic
- Life Science Research Centre, Department of Biology and Ecology, Faculty of Science, University of Ostrava, Ostrava, Czech Republic
- Division of Infectious Diseases, Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Canada
| | - Corinna Benz
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
| | - Joel B Dacks
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
- Division of Infectious Diseases, Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Canada
- Centre for Life's Origins and Evolution, Department of Genetics, Evolution, and Environment, University College London, London, UK
| | - Mark C Field
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
- School of Life Sciences, University of Dundee, Dundee, UK
| | - Julius Lukeš
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
- Faculty of Sciences, University of South Bohemia, České Budějovice, Czech Republic
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3
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Zuma AA, Dos Santos Barrias E, de Souza W. Basic Biology of Trypanosoma cruzi. Curr Pharm Des 2021; 27:1671-1732. [PMID: 33272165 DOI: 10.2174/1381612826999201203213527] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Revised: 10/01/2020] [Accepted: 10/08/2020] [Indexed: 11/22/2022]
Abstract
The present review addresses basic aspects of the biology of the pathogenic protozoa Trypanosoma cruzi and some comparative information of Trypanosoma brucei. Like eukaryotic cells, their cellular organization is similar to that of mammalian hosts. However, these parasites present structural particularities. That is why the following topics are emphasized in this paper: developmental stages of the life cycle in the vertebrate and invertebrate hosts; the cytoskeleton of the protozoa, especially the sub-pellicular microtubules; the flagellum and its attachment to the protozoan body through specialized junctions; the kinetoplast-mitochondrion complex, including its structural organization and DNA replication; glycosome and its role in the metabolism of the cell; acidocalcisome, describing its morphology, biochemistry, and functional role; cytostome and the endocytic pathway; the organization of the endoplasmic reticulum and Golgi complex; the nucleus, describing its structural organization during interphase and division; and the process of interaction of the parasite with host cells. The unique characteristics of these structures also make them interesting chemotherapeutic targets. Therefore, further understanding of cell biology aspects contributes to the development of drugs for chemotherapy.
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Affiliation(s)
- Aline A Zuma
- Laboratorio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho - Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Emile Dos Santos Barrias
- Laboratorio de Metrologia Aplicada a Ciencias da Vida, Diretoria de Metrologia Aplicada a Ciencias da Vida - Instituto Nacional de Metrologia, Qualidade e Tecnologia (Inmetro), Rio de Janeiro, Brazil
| | - Wanderley de Souza
- Laboratorio de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho - Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
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Maudlin IE, Kelly S, Schwede A, Carrington M. VSG mRNA levels are regulated by the production of functional VSG protein. Mol Biochem Parasitol 2021; 241:111348. [PMID: 33352254 PMCID: PMC7871013 DOI: 10.1016/j.molbiopara.2020.111348] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 12/15/2020] [Accepted: 12/16/2020] [Indexed: 02/06/2023]
Abstract
The bloodstream form of Trypanosoma brucei persists in mammalian hosts through a population survival strategy depending on antigenic variation of a cell surface coat composed of the variant surface glycoprotein (VSG). The integrity of the VSG coat is essential and blocking its synthesis results in a cell division cycle arrest just prior to cytokinesis. This observation indicates that VSG levels are monitored and that the cell has mechanisms to respond to a disruption of synthesis. Here, the regulation of VSG mRNA levels has been investigated by first measuring VSG mRNA copy number, and second using ectopic expression of VSG transgenes containing premature termination codons. The findings are that (i) VSG mRNA copy number varies with the identity of the VSG and (ii) a pathway detects synthesis of non-functional VSG protein and results in an increase in VSG mRNA levels.
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Affiliation(s)
- Isabella E Maudlin
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom
| | - Steve Kelly
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, United Kingdom
| | - Angela Schwede
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom.
| | - Mark Carrington
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom.
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5
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Venkatesh D, Zhang N, Zoltner M, del Pino RC, Field MC. Evolution of protein trafficking in kinetoplastid parasites: Complexity and pathogenesis. Traffic 2018; 19:803-812. [DOI: 10.1111/tra.12601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 06/24/2018] [Accepted: 06/25/2018] [Indexed: 12/31/2022]
Affiliation(s)
| | - Ning Zhang
- School of Life Sciences; University of Dundee; Dundee UK
| | - Martin Zoltner
- School of Life Sciences; University of Dundee; Dundee UK
| | | | - Mark C. Field
- School of Life Sciences; University of Dundee; Dundee UK
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6
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Woelke MR, Paulucci NS, Selva A, Garban H, de Lema MG. Δ9 desaturase from Trypanosoma cruzi : Key enzyme in the parasite metabolism. Cloning and overexpression. Microbiol Res 2017; 194:29-37. [DOI: 10.1016/j.micres.2016.07.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 07/03/2016] [Accepted: 07/31/2016] [Indexed: 10/20/2022]
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7
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Cheung JLY, Wand NV, Ooi CP, Ridewood S, Wheeler RJ, Rudenko G. Blocking Synthesis of the Variant Surface Glycoprotein Coat in Trypanosoma brucei Leads to an Increase in Macrophage Phagocytosis Due to Reduced Clearance of Surface Coat Antibodies. PLoS Pathog 2016; 12:e1006023. [PMID: 27893860 PMCID: PMC5125712 DOI: 10.1371/journal.ppat.1006023] [Citation(s) in RCA: 18] [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: 05/02/2016] [Accepted: 10/25/2016] [Indexed: 11/19/2022] Open
Abstract
The extracellular bloodstream form parasite Trypanosoma brucei is supremely adapted to escape the host innate and adaptive immune system. Evasion is mediated through an antigenically variable Variant Surface Glycoprotein (VSG) coat, which is recycled at extraordinarily high rates. Blocking VSG synthesis triggers a precytokinesis arrest where stalled cells persist for days in vitro with superficially intact VSG coats, but are rapidly cleared within hours in mice. We therefore investigated the role of VSG synthesis in trypanosome phagocytosis by activated mouse macrophages. T. brucei normally effectively evades macrophages, and induction of VSG RNAi resulted in little change in phagocytosis of the arrested cells. Halting VSG synthesis resulted in stalled cells which swam directionally rather than tumbling, with a significant increase in swim velocity. This is possibly a consequence of increased rigidity of the cells due to a restricted surface coat in the absence of VSG synthesis. However if VSG RNAi was induced in the presence of anti-VSG221 antibodies, phagocytosis increased significantly. Blocking VSG synthesis resulted in reduced clearance of anti-VSG antibodies from the trypanosome surface, possibly as a consequence of the changed motility. This was particularly marked in cells in the G2/ M cell cycle stage, where the half-life of anti-VSG antibody increased from 39.3 ± 4.2 seconds to 99.2 ± 15.9 seconds after induction of VSG RNAi. The rates of internalisation of bulk surface VSG, or endocytic markers like transferrin, tomato lectin or dextran were not significantly affected by the VSG synthesis block. Efficient elimination of anti-VSG-antibody complexes from the trypanosome cell surface is therefore essential for trypanosome evasion of macrophages. These experiments highlight the essentiality of high rates of VSG recycling for the rapid removal of host opsonins from the parasite surface, and identify this process as a key parasite virulence factor during a chronic infection.
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Affiliation(s)
- Jackie L. Y. Cheung
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Nadina V. Wand
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Cher-Pheng Ooi
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Sophie Ridewood
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Richard J. Wheeler
- Department of Pathology, Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Gloria Rudenko
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
- * E-mail:
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Allison H, O'Reilly AJ, Sternberg J, Field MC. An extensive endoplasmic reticulum-localised glycoprotein family in trypanosomatids. MICROBIAL CELL 2014; 1:325-345. [PMID: 26167471 PMCID: PMC4497807 DOI: 10.15698/mic2014.10.170] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
African trypanosomes are evolutionarily highly divergent parasitic protozoa, and
as a consequence the vast majority of trypanosome membrane proteins remain
uncharacterised in terms of location, trafficking or function. Here we describe
a novel family of type I membrane proteins which we designate ‘invariant
glycoproteins’ (IGPs). IGPs are trypanosome-restricted, with extensive,
lineage-specific paralogous expansions in related taxa. In T.
brucei three IGP subfamilies, IGP34, IGP40 and IGP48 are
recognised; all possess a putative C-type lectin ectodomain and are
ER-localised, despite lacking a classical ER-retention motif. IGPs exhibit
highest expression in stumpy stage cells, suggesting roles in developmental
progression, but gene silencing in mammalian infective forms suggests that each
IGP subfamily is also required for normal proliferation. Detailed analysis of
the IGP48 subfamily indicates a role in maintaining ER morphology, while the ER
lumenal domain is necessary and sufficient for formation of both oligomeric
complexes and ER retention. IGP48 is detected by antibodies from T. b.
rhodesiense infected humans. We propose that the IGPs represent a
trypanosomatid-specific family of ER-localised glycoproteins, with potential
contributions to life cycle progression and immunity, and utilise
oligomerisation as an ER retention mechanism.
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Affiliation(s)
- Harriet Allison
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, Scotland, DD1 5EH
| | - Amanda J O'Reilly
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, Scotland, DD1 5EH
| | - Jeremy Sternberg
- School of Biological Sciences, University of Aberdeen, Aberdeen, AB24 2TZ, UK
| | - Mark C Field
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, Scotland, DD1 5EH
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Manna PT, Boehm C, Leung KF, Natesan SK, Field MC. Life and times: synthesis, trafficking, and evolution of VSG. Trends Parasitol 2014; 30:251-8. [PMID: 24731931 PMCID: PMC4007029 DOI: 10.1016/j.pt.2014.03.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Revised: 03/14/2014] [Accepted: 03/14/2014] [Indexed: 11/30/2022]
Abstract
Evasion of the acquired immune response in African trypanosomes is principally mediated by antigenic variation, the sequential expression of distinct variant surface glycoproteins (VSGs) at extremely high density on the cell surface. Sequence diversity between VSGs facilitates escape of a subpopulation of trypanosomes from antibody-mediated killing. Significant advances have increased understanding of the mechanisms underpinning synthesis and maintenance of the VSG coat. In this review, we discuss the biosynthesis, trafficking, and turnover of VSG, emphasising those unusual mechanisms that act to maintain coat integrity and to protect against immunological attack. We also highlight new findings that suggest the presence of unique or highly divergent proteins that may offer therapeutic opportunities, as well as considering aspects of VSG biology that remain to be fully explored.
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Affiliation(s)
- Paul T Manna
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, DD1 5EH, UK
| | - Cordula Boehm
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, DD1 5EH, UK
| | - Ka Fai Leung
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Senthil Kumar Natesan
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Mark C Field
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, DD1 5EH, UK.
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Evidence for recycling of invariant surface transmembrane domain proteins in African trypanosomes. EUKARYOTIC CELL 2012; 12:330-42. [PMID: 23264644 DOI: 10.1128/ec.00273-12] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Intracellular trafficking is a vital component of both virulence mechanisms and drug interactions in Trypanosoma brucei, the causative agent of human African trypanosomiasis and n'agana of cattle. Both maintaining the surface proteome composition within a life stage and remodeling the composition when progressing between life stages are important features of immune evasion and development for trypanosomes. Our recent work implicates the abundant transmembrane invariant surface glycoproteins (ISGs) in the uptake of first-line therapeutic suramin, suggesting a potential therapeutic route into the cell. RME-8 is a mediator of recycling pathways in higher eukaryotes and is one of a small cohort of intracellular transport gene products upregulated in mammal-infective trypanosomes, suggesting a role in controlling the copy number of surface proteins in trypanosomes. Here we investigate RME-8 function and its contribution to intracellular trafficking and stability of ISGs. RME-8 is a highly conserved protein and is broadly distributed across multiple endocytic compartments. By knockdown we find that RME-8 is essential and mediates delivery of endocytic probes to late endosomal compartments. Further, we find ISG accumulation within endosomes, but that RME-8 knockdown also increases ISG turnover; combined with previous data, this suggests that it is most probable that ISGs are recycled, and that RME-8 is required to support recycling.
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Ubiquitylation and developmental regulation of invariant surface protein expression in trypanosomes. EUKARYOTIC CELL 2011; 10:916-31. [PMID: 21571921 DOI: 10.1128/ec.05012-11] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The cell surface of Trypanosoma brucei is dominated by the glycosylphosphatidylinositol-anchored variant surface glycoprotein (VSG), which is essential for immune evasion. VSG biosynthesis, trafficking, and turnover are well documented, but trans-membrane domain (TMD) proteins, including the invariant surface glycoproteins (ISGs), are less well characterized. Internalization and degradation of ISG65 depend on ubiquitylation of conserved cytoplasmic lysines. Using epitope-tagged ISG75 and reporter chimeric proteins bearing the cytoplasmic and trans-membrane regions of ISG75, together with multiple mutants with lysine-to-arginine mutations, we demonstrate that the cytoplasmic tail of ISG75 is both sufficient and necessary for endosomal targeting and degradation. The ISG75 chimeric reporter protein localized to endocytic organelles, while lysine-null versions were significantly stabilized at the cell surface. Importantly, ISG75 cytoplasmic lysines are modified by extensive oligoubiquitin chains and ubiquitylation is abolished in the lysine-null version. Furthermore, we find evidence for differential modes of turnover of ISG65 and ISG75. Full-length lysine-null ISG65 localization and protein turnover are significantly perturbed, but ISG75 localization and protein turnover are not, while ubiquitin conjugates can be detected for full-length lysine-null ISG75 but not ISG65. We find that the ISG75 ectodomain has a predicted coiled-coil, suggesting that ISG75 could be part of a complex, while ISG65 behaves independently. We also demonstrate a developmental stage-specific mechanism for exclusion of surface ISG expression in insect-stage cells by a ubiquitin-independent mechanism. We suggest that ubiquitylation may be a general mechanism for regulating trans-membrane domain surface proteins in trypanosomes.
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