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Abstract
The trypanosomes cause two neglected tropical diseases, Chagas disease in the Americas and African trypanosomiasis in sub-Saharan Africa. Over recent years a raft of molecular tools have been developed enabling the genetic dissection of many aspects of trypanosome biology, including the mechanisms underlying resistance to some of the current clinical and veterinary drugs. This has led to the identification and characterization of key resistance determinants, including transporters for the anti-Trypanosoma brucei drugs, melarsoprol, pentamidine and eflornithine, and the activator of nifurtimox-benznidazole, the anti-Trypanosoma cruzi drugs. More recently, advances in sequencing technology, combined with the development of RNA interference libraries in the clinically relevant bloodstream form of T. brucei have led to an exponential increase in the number of proteins known to interact either directly or indirectly with the anti-trypanosomal drugs. In this review, we discuss these findings and the technological developments that are set to further revolutionise our understanding of drug-trypanosome interactions. The new knowledge gained should inform the development of novel interventions against the devastating diseases caused by these parasites.
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Peck RF, Shiflett AM, Schwartz KJ, McCann A, Hajduk SL, Bangs JD. The LAMP-like protein p67 plays an essential role in the lysosome of African trypanosomes. Mol Microbiol 2008; 68:933-46. [PMID: 18430083 DOI: 10.1111/j.1365-2958.2008.06195.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
RNAi knockdown was employed to study the function of p67, a lysosome-associated membrane protein (LAMP)-like type I transmembrane lysosomal glycoprotein in African trypanosomes. Conditional induction of p67 dsRNA resulted in specific approximately 90% reductions in de novo p67 synthesis in both mammalian bloodstream and procyclic insect-stage parasites. Bloodstream cell growth was severely retarded with extensive death after > 24 h of induction. Biosynthetic trafficking of residual p67, and of the soluble lysosomal protease trypanopain, were unimpaired. Endocytosis of tomato lectin, a surrogate receptor-mediated cargo, was only mildly impaired (approximately 20%), but proper lysosomal targeting was unaffected. p67 ablation had dramatic effects on lysosomal morphology with gross enlargement (four- to fivefold) and internal membrane profiles reminiscent of autophagic vacuoles. Ablation of p67 expression rendered bloodstream trypanosomes refractory to lysis by human trypanolytic factor (TLF), a lysosomally activated host innate immune mediator. Similar effects on lysosomal morphology and TLF sensitivity were also obtained by two pharmacological agents that neutralize lysosomal pH--chloroquine and bafilomycin A1. Surprisingly, however, lysosomal pH was not affected in ablated cells suggesting that other physiological alterations must account for increased resistance to TLF. These results indicate p67 plays an essential role in maintenance of normal lysosomal structure and physiology in bloodstream-stage African trypanosomes.
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Affiliation(s)
- Ronald F Peck
- Department of Medical Microbiology & Immunology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA
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Li Z, Gourguechon S, Wang CC. Tousled-like kinase in a microbial eukaryote regulates spindle assembly and S-phase progression by interacting with Aurora kinase and chromatin assembly factors. J Cell Sci 2007; 120:3883-94. [DOI: 10.1242/jcs.007955] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Tousled-like kinases are an evolutionarily conserved family of proteins implicated in DNA repair, DNA replication and mitosis in metazoans and plants. Their absence from the yeasts and other eukaryotic `microbes' suggests a specific role for them in the development of multicellular organisms. In this study, two closely related Tousled-like kinase homologs, TLK1 and TLK2, were identified in Trypanosoma brucei, a unicellular protozoan parasite. Only TLK1 plays an essential role in cell growth, and a deficiency in TLK1 led to an enrichment of S-phase cells, defective spindle formation and aberrant chromosome segregation. Although both TLK proteins localize to the nucleus, only TLK1 also concentrates in the spindle poles during mitosis. Both TLK proteins are phosphorylated by the Aurora kinase (AUK1), and both can autophosphorylate and phosphorylate histone H3 and the chromatin assembly factors Asf1A and Asf1B in vitro, but only TLK1 is autophosphorylated and capable of oligomerizing and interacting with AUK1, Asf1A and Asf1B in vivo. These discrepancies between the two TLK proteins can be attributed to minor differences between their N- and C-terminal sequences. In summary, TLK1 cooperates with Aurora kinase to regulate spindle assembly and chromosome segregation, and it performs a role in DNA replication probably by regulating histone modification in trypanosomes.
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Affiliation(s)
- Ziyin Li
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2280, USA
| | - Stéphane Gourguechon
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2280, USA
| | - Ching C. Wang
- Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158-2280, USA
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Kelly S, Reed J, Kramer S, Ellis L, Webb H, Sunter J, Salje J, Marinsek N, Gull K, Wickstead B, Carrington M. Functional genomics in Trypanosoma brucei: a collection of vectors for the expression of tagged proteins from endogenous and ectopic gene loci. Mol Biochem Parasitol 2007; 154:103-9. [PMID: 17512617 PMCID: PMC2705915 DOI: 10.1016/j.molbiopara.2007.03.012] [Citation(s) in RCA: 157] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2007] [Revised: 03/20/2007] [Accepted: 03/21/2007] [Indexed: 11/23/2022]
Affiliation(s)
- Steven Kelly
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
| | - Jenny Reed
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Susanne Kramer
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Louise Ellis
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Helena Webb
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Jack Sunter
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Jeanne Salje
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Nina Marinsek
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Keith Gull
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
| | - Bill Wickstead
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
| | - Mark Carrington
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
- Corresponding author. Tel.: +44 1223 333683; fax: +44 1223 766002.
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Shi H, Chamond N, Tschudi C, Ullu E. Selection and characterization of RNA interference-deficient trypanosomes impaired in target mRNA degradation. EUKARYOTIC CELL 2005; 3:1445-53. [PMID: 15590819 PMCID: PMC539030 DOI: 10.1128/ec.3.6.1445-1453.2004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Genetic analysis of the RNA interference (RNAi) pathway in Trypanosoma brucei has so far revealed one essential component, namely, TbAGO1, encoding a member of the Argonaute protein family. To gain further insight into the RNAi mechanism and its biological significance, we selected RNAi-deficient trypanosomes by using repeated cycles of electroporation with alpha-tubulin double-stranded RNA, a treatment that blocks cytokinesis in wild-type cells. Two independent clones, termed RiD-1 (for RNAi-deficient clone 1) and RiD-2, were characterized. At the cellular level, only RiD-1 trypanosomes showed a significant increase in doubling time with the concomitant accumulation of cells defective in the completion of cytokinesis. At the RNA level, both clones accumulated wild-type amounts of small interfering RNAs and displayed elevated levels of retroposon transcripts, the hallmark of RNAi deficiency in T. brucei. Importantly, both RiD-1 and RiD-2 clones were defective in the degradation of target mRNA, suggesting an impairment of the activity of AGO1, the putative RNAi endonuclease. Since in RiD cells the AGO1 gene was not mutated and was expressed at wild-type levels, we propose that in trypanosomes the cleavage of mRNA by AGO1 is regulated by the interaction with another factor(s).
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Affiliation(s)
- Huafang Shi
- Department of Internal Medicine, Yale Medical School, BCMM 136D, 295 Congress Ave., Box 9812, New Haven, CT 06536-8012, USA
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Li Z, Zou CB, Yao Y, Hoyt MA, McDonough S, Mackey ZB, Coffino P, Wang CC. An easily dissociated 26 S proteasome catalyzes an essential ubiquitin-mediated protein degradation pathway in Trypanosoma brucei. J Biol Chem 2002; 277:15486-98. [PMID: 11854272 DOI: 10.1074/jbc.m109029200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 26 S proteasome, a complex between the 20 S proteasome and 19 S regulatory units, catalyzes ATP-dependent degradation of unfolded and ubiquitinated proteins in eukaryotes. We have identified previously 20 S and activated 20 S proteasomes in Trypanosoma brucei, but not 26 S proteasome. However, the presence of 26 S proteasome in T. brucei was suggested by the hydrolysis of casein by cell lysate, a process that requires ATP but is inhibited by lactacystin, and the lactacystin-sensitive turnover of ubiquitinated proteins in the intact cells. T. brucei cDNAs encoding the six proteasome ATPase homologues (Rpt) were cloned and expressed. Five of the six T. brucei Rpt cDNAs, except for Rpt2, were capable of functionally complementing the corresponding rpt deletion mutants of Saccharomyces cerevisiae. Immunoblots showed the presence in T. brucei lysate of the Rpt proteins, which co-fractionated with the yeast 19 S proteasome complex by gel filtration and localized in the 19 S fraction of a glycerol gradient. All the Rpt and putative 19 S non-ATPase (Rpn) proteins were co-immunoprecipitated from T. brucei lysate by individual anti-Rpt antibodies. Treatment of T. brucei cells with a chemical cross-linker resulted in co-immunoprecipitation of 20 S proteasome with all the Rpt and Rpn proteins that sedimented in a glycerol gradient to the position of 26 S proteasome. These data demonstrate the presence of 26 S proteasome in T. brucei cells, which apparently dissociate into 19 S and 20 S complexes upon cell lysis. RNA interference to block selectively the expression of proteasome 20 S core and Rpt subunits resulted in significant accumulation of ubiquitinated proteins accompanied by cessation of cell growth. Expression of yeast RPT2 gene in T. brucei Rpt2-deficient cells could not rescue the lethal phenotype, thus confirming the incompatibility between the two Rpt2s. The T. brucei 11 S regulator (PA26)-deficient RNA interference cells grew normally, suggesting the dispensability of activated 20 S proteasome in T. brucei.
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Affiliation(s)
- Ziyin Li
- Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143-0446, USA
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Tetaud E, Lecuix I, Sheldrake T, Baltz T, Fairlamb AH. A new expression vector for Crithidia fasciculata and Leishmania. Mol Biochem Parasitol 2002; 120:195-204. [PMID: 11897125 DOI: 10.1016/s0166-6851(02)00002-6] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Crithidia fasciculata is a monogenetic parasite of insects. It grows in fully defined media without requiring serum, which facilitates biochemical analysis. We have constructed a series of expression systems that allows expression of transfected genes in the kinetoplastid protozoa Crithidia and Leishmania. These cells can be readily transfected with plasmid DNA by electroporation and transformants selected with various antibiotic resistance markers. 5'-Trans-splicing signals and poorly defined regions within the 3'-untranslated regions of genes are required for optimal expression of genes in trypanosomatids. We, therefore, inserted the intergenic region of the C. fasciculata phosphoglycerate kinase (PGK) genes A and B, which allows polyadenylation of the target gene and spliced leader addition to the selectable marker gene. Part of the intergenic region of the PGK locus was added upstream of the target gene to permit its trans-splicing. A 3'-untranslated sequence from the Crithidia glutathionylspermidine synthetase (GSPS) was also added to allow the polyadenylation of the selectable marker gene. Genes can be readily inserted using a multiple cloning site and can be expressed as a fusion protein with a poly-histidine sequence at either the N or C-terminus or fused with green fluorescent protein. Biologically active proteins can be expressed in C. fasciculata or L. amazonensis promastigotes and purified by affinity chromatography using a metal chelating column.
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Affiliation(s)
- Emmanuel Tetaud
- Division of Biological Chemistry and Molecular Microbiology, School of Life Sciences, The Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, UK.
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Gasser RB, Newton SE. Genomic and genetic research on bursate nematodes: significance, implications and prospects. Int J Parasitol 2000; 30:509-34. [PMID: 10731573 DOI: 10.1016/s0020-7519(00)00021-7] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Molecular genetic research on parasitic nematodes (order Strongylida) is of major significance for many fundamental and applied areas of medical and veterinary parasitology. The advent of gene technology has led to some progress for this group of nematodes, particularly in studying parasite systematics, drug resistance and population genetics, and in the development of diagnostic assays and the characterisation of potential vaccine and drug targets. This paper gives an account of the molecular biology and genetics of strongylid nematodes, mainly of veterinary socio-economic importance, indicates the implications of such research and gives a perspective on genome research for this important parasite group, in light of recent technological advances and knowledge of the genomes of other metazoan organisms.
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Affiliation(s)
- R B Gasser
- Department of Veterinary Science, The University of Melbourne, 250 Princes Highway, Werribee, Victoria, Australia.
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Abstract
During the 1980s, many kinetoplastid genes were cloned and their function inferred from homology with genes from other organisms, location of the corresponding proteins or expression in heterologous systems. Up until 1990, before the availability of DNA transfection methodology, we could not analyze the function of kinetoplastid genes within the organisms themselves. Since then, it has become possible to create and complement mutants, to overexpress foreign proteins in the parasites, to knock out genes and even to switch off essential functions. However, these methods are not equally applicable in all parasites. Here, Christine Clayton highlights the differences and similarities between the most commonly used model organisms, and assesses the relative advantages of different approaches and parasites for different types of investigation.
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Affiliation(s)
- C E Clayton
- Zentrum für Molekulare Biologie (ZMBH), Im Neuenheimer Feld 282, Postfach 106249, D-69120 Heidelberg, Germany.
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Hwa KY, Acosta-Serrano A, Khoo KH, Pearson T, Englund PT. Protein glycosylation mutants of procyclic Trypanosoma brucei: defects in the asparagine-glycosylation pathway. Glycobiology 1999; 9:181-90. [PMID: 9949195 DOI: 10.1093/glycob/9.2.181] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We employed a genetic approach to study protein glycosylation in the procyclic form of the parasite Trypanosoma brucei. Two different mutant parasites, ConA 1-1 and ConA 4-1, were isolated from mutagenized cultures by selecting cells which resisted killing or agglutination by concanavalin A. Both mutant cells show reduced concanavalin A binding. However, the mutants have different phenotypes, as indicated by the fact that ConA 1-1 binds to wheat germ agglutinin but ConA 4-1 and wild type do not. A blot probed with concanavalin A revealed that many proteins in both mutants lost the ability to bind this lectin, and the blots resembled one of wild type membrane proteins treated with PNGase F. This finding suggested that the mutants had altered asparagine-linked glycosylation. This conclusion was confirmed by studies on a flagellar protein (Fla1) and procyclic acidic repetitive protein (PARP). Structural analysis indicated that the N- glycan of wild type PARP is exclusively Man5GlcNAc2 whereas that in both mutants is predominantly a hybrid type with a terminal N- acetyllactosamine. The occupancy of the PARP glycosylation site in ConA 4-1 was much lower than that in ConA 1-1. These mutants will be useful for studying trypanosome glycosylation mechanisms and function.
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Affiliation(s)
- K Y Hwa
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Mutomba MC, Li F, Gottesdiener KM, Wang CC. A Trypanosoma brucei bloodstream form mutant deficient in ornithine decarboxylase can protect against wild-type infection in mice. Exp Parasitol 1999; 91:176-84. [PMID: 9990346 DOI: 10.1006/expr.1998.4363] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A Trypanosoma brucei bloodstream mutant in which both copies of the ornithine decarboxylase (ODC) gene were knocked out (ODC mutant) was used to determine the biological functions of ODC in T. brucei. Growth of the mutant cells ceased within 12-24 h in regular culture medium deficient in polyamines, but could be rescued by supplementation with 1 mM putrescine. A mouse model of T. brucei infection was used to determine whether the mutant was still infective and was found to develop either extremely low or undetectable levels of parasitemia, suggesting that in T. brucei, ODC activity is essential for establishing an infection. Furthermore, when these mice were subsequently challenged with wild-type T. brucei cells expressing the same variant surface glycoprotein (VSG), they did not develop any parasitemia, indicating that inoculating the mice with the attenuated ODC mutant had conferred protection against challenge by wild-type cells. These results were reproduced in C57BL/6J mice deficient in alpha-beta and gamma-delta T-cell receptors. However, no protection was observed in rag-2 knockout mice deficient in both B and T lymphocytes or in C57BL/10J mice deficient only in B lymphocytes. The results thus suggest that the ODC mutant could induce a T-lymphocyte-independent but B-lymphocyte-dependent immunity against wild-type cells of the same VSG. Such a mechanism of immunity has been elicited only by live T. brucei cells, but not by isolated VSGs or radiation-killed trypanosomes. This ODC mutant may thus represent a genuinely attenuated T. brucei bloodstream form capable of immunizing mammals against infections by African trypanosomes of the same VSG subtype without causing detectable infection by itself. The observation also raises the interesting likelihood that the in vivo treatment of T. brucei bloodstream forms with alpha-DL-difluoromethylornithine is a de facto attenuation of the parasitic organisms, which may very well result in B-lymphocyte-dependent host immune responses to subsequent infections by parasites of the same VSG subtypes.
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Affiliation(s)
- M C Mutomba
- Department of Pharmaceutical Chemistry, University of California, San Francisco 94143-0446, USA
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Hwang HY, Gilberts T, Jardim A, Shih S, Ullman B. Creation of homozygous mutants of Leishmania donovani with single targeting constructs. J Biol Chem 1996; 271:30840-6. [PMID: 8940067 DOI: 10.1074/jbc.271.48.30840] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Homozygous null mutants of the hypoxanthine-guanine phosphoribosyltransferase (hgprt) and adenine phosphoribosyltransferase (aprt) loci were created in Leishmania donovani in which both alleles were eliminated using only a single targeting construct. Functional heterozygotes were first generated by homologous recombination after transfection with vectors containing 5'- and 3'-flanking regions of either the hgprt or the aprt gene circumscribing drug resistance markers. Homozygous null mutants were then isolated from the heterozygotes by negative selection in media containing subversive substrates of the encoded proteins, i.e. allopurinol for HGPRT and 4-aminopyrazolopyrimidine for APRT. The novel alleles created by homologous recombination were verified by Southern blotting, and the effects of gene replacement upon gene expression in intact parasites were evaluated by direct enzymatic assay and by immunoblotting. All mutant strains were viable under the selection conditions and exhibited appropriate drug resistance phenotypes. The ability to generate homozygous knockouts with single targeting constructs greatly facilitates the genetic dissection and subsequent biochemical investigations of the purine pathway in Leishmania and has important general implications for the genetic manipulation and analysis of the leishmanial genome.
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Affiliation(s)
- H Y Hwang
- Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland, Oregon 97201-3098, USA.
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