scholarly journals Genetic Validation of Trypanosoma brucei Glutathione Synthetase as an Essential Enzyme

2014 ◽  
Vol 13 (5) ◽  
pp. 614-624 ◽  
Author(s):  
Chelsea Pratt ◽  
Suong Nguyen ◽  
Margaret A. Phillips
Keyword(s):  
Trypanosoma Brucei ◽  
Drug Targets ◽  
Glutathione Synthetase ◽  
Biosynthetic Enzymes ◽  
Polyamine Biosynthesis ◽  
Content Type ◽  
Stage Disease ◽  
Trypanosomatid Parasites ◽  
Vector Borne ◽  
Essential Enzyme

ABSTRACTHuman African trypanosomiasis (HAT) is a debilitating and fatal vector-borne disease. Polyamine biosynthesis is the target of one of the key drugs (eflornithine) used for the treatment of late-stage disease, suggesting that the pathway might be exploited for the identification of additional drug targets. The polyamine spermidine is required in trypanosomatid parasites for formation of a unique redox cofactor termed trypanothione, which is formed from the conjugation of glutathione to spermidine. Here we characterize recombinantTrypanosoma bruceiglutathione synthetase (TbGS) and show that depletion ofTbGS in blood-form parasites using a regulated knockout strategy leads to loss of trypanothione and to cell death as quantified by fluorescence-activated cell sorter (FACS) analysis. These data suggest that >97% depletion ofTbGS is required before trypanothione is depleted and cell growth arrest is observed. Exogenous glutathione was able to partially compensate for the loss ofTbGS, suggesting that parasites are able to transport intact glutathione. Finally, reduced expression ofTbGS leads to increased levels of upstream glutathione biosynthetic enzymes and decreased expression of polyamine biosynthetic enzymes, providing evidence that the cells cross regulate the two branches of the trypanothione biosynthetic pathway to maintain spermidine and trypanothione homeostasis.

scholarly journals Pharmacological Inhibition of the Vacuolar ATPase in Bloodstream-Form Trypanosoma brucei Rescues Genetic Knockdown of Mitochondrial Gene Expression

2018 ◽  
Vol 62 (9) ◽  
Author(s):  
Claudia Schaffner-Barbero ◽  
Migla Miskinyte ◽  
Jaspreet Singh Grewal ◽  
Achim Schnaufer
Keyword(s):  
Gene Expression ◽  
Trypanosoma Brucei ◽  
Mitochondrial Gene ◽  
Vacuolar Atpase ◽  
Mitochondrial Gene Expression ◽  
Term Survival ◽  
Content Type ◽  
Trypanosomatid Parasites ◽  
Atpase Inhibition

ABSTRACT Trypanosomatid parasites cause diseases in humans and livestock. It was reported that partial inhibition of the vacuolar ATPase (V-ATPase) affects the dependence of Trypanosoma brucei on its mitochondrial genome (kinetoplast DNA [kDNA]), a target of the antitrypanosomatid drug isometamidium. Here, we report that V-ATPase inhibition with bafilomycin A1 (BafA) provides partial resistance to genetic knockdown of mitochondrial gene expression. BafA does not promote long-term survival after kDNA loss, but in its presence, isometamidium causes less damage to kDNA.

scholarly journals Selective Inhibitors of Methionyl-tRNA Synthetase Have Potent Activity against Trypanosoma brucei Infection in Mice

2011 ◽  
Vol 55 (5) ◽  
pp. 1982-1989 ◽  
Author(s):  
Sayaka Shibata ◽  
J. Robert Gillespie ◽  
Angela M. Kelley ◽  
Alberto J. Napuli ◽  
Zhongsheng Zhang ◽  
...  
Keyword(s):  
Cell Growth ◽  
Trypanosoma Brucei ◽  
Drug Targets ◽  
Treatment Options ◽  
Therapeutic Index ◽  
Comparative Sequence Analysis ◽  
Trna Synthetase ◽  
Sub Saharan Africa ◽  
Content Type ◽  
Trna Synthetases

ABSTRACTHuman African trypanosomiasis continues to be an important public health threat in extensive regions of sub-Saharan Africa. Treatment options for infected patients are unsatisfactory due to toxicity, difficult administration regimes, and poor efficacy of available drugs. The aminoacyl-tRNA synthetases were selected as attractive drug targets due to their essential roles in protein synthesis and cell survival. Comparative sequence analysis disclosed differences between the trypanosome and mammalian methionyl-tRNA synthetases (MetRSs) that suggested opportunities for selective inhibition using drug-like molecules. Experiments using RNA interference on the single MetRS ofTrypanosoma bruceidemonstrated that this gene product was essential for normal cell growth. Small molecules (diaryl diamines) similar to those shown to have potent activity on prokaryotic MetRS enzymes were synthesized and observed to have inhibitory activity on theT. bruceiMetRS (50% inhibitory concentration, <50 nM) and on bloodstream forms ofT. bruceicultures (50% effective concentration, as low as 4 nM). Twenty-one compounds had a close correlation between enzyme binding/inhibition andT. bruceigrowth inhibition, indicating that they were likely to be acting on the intended target. The compounds had minimal effects on mammalian cell growth at 20 μM, demonstrating a wide therapeutic index. The most potent compound was tested in the murine model of trypanosomiasis and demonstrated profound parasite suppression and delayed mortality. A homology model of theT. bruceiMetRS based on other MetRS structures was used to model binding of the lead diaryl diamine compounds. Future studies will focus on improving the pharmacological properties of the MetRS inhibitors.

scholarly journals Genetic Validation of Aminoacyl-tRNA Synthetases as Drug Targets in Trypanosoma brucei

2014 ◽  
Vol 13 (4) ◽  
pp. 504-516 ◽  
Author(s):  
Savitha Kalidas ◽  
Igor Cestari ◽  
Severine Monnerat ◽  
Qiong Li ◽  
Sandesh Regmi ◽  
...  
Keyword(s):  
Drug Discovery ◽  
Trypanosoma Brucei ◽  
Drug Targets ◽  
Trna Synthetase ◽  
New Drugs ◽  
Sub Saharan Africa ◽  
Content Type ◽  
Trna Synthetases ◽  
Aminoacyl Trna Synthetases

ABSTRACT Human African trypanosomiasis (HAT) is an important public health threat in sub-Saharan Africa. Current drugs are unsatisfactory, and new drugs are being sought. Few validated enzyme targets are available to support drug discovery efforts, so our goal was to obtain essentiality data on genes with proven utility as drug targets. Aminoacyl-tRNA synthetases (aaRSs) are known drug targets for bacterial and fungal pathogens and are required for protein synthesis. Here we survey the essentiality of eight Trypanosoma brucei aaRSs by RNA interference (RNAi) gene expression knockdown, covering an enzyme from each major aaRS class: valyl-tRNA synthetase (ValRS) (class Ia), tryptophanyl-tRNA synthetase (TrpRS-1) (class Ib), arginyl-tRNA synthetase (ArgRS) (class Ic), glutamyl-tRNA synthetase (GluRS) (class 1c), threonyl-tRNA synthetase (ThrRS) (class IIa), asparaginyl-tRNA synthetase (AsnRS) (class IIb), and phenylalanyl-tRNA synthetase (α and β) (PheRS) (class IIc). Knockdown of mRNA encoding these enzymes in T. brucei mammalian stage parasites showed that all were essential for parasite growth and survival in vitro . The reduced expression resulted in growth, morphological, cell cycle, and DNA content abnormalities. ThrRS was characterized in greater detail, showing that the purified recombinant enzyme displayed ThrRS activity and that the protein localized to both the cytosol and mitochondrion. Borrelidin, a known inhibitor of ThrRS, was an inhibitor of T. brucei ThrRS and showed antitrypanosomal activity. The data show that aaRSs are essential for T. brucei survival and are likely to be excellent targets for drug discovery efforts.

scholarly journals Fungal Homoserine Kinase (thr1Δ) Mutants Are Attenuated in Virulence and Die Rapidly upon Threonine Starvation and Serum Incubation

2010 ◽  
Vol 9 (5) ◽  
pp. 729-737 ◽  
Author(s):  
Joanne M. Kingsbury ◽  
John H. McCusker
Keyword(s):  
Drug Targets ◽  
Antifungal Drug ◽  
Aspartate Kinase ◽  
Biosynthetic Enzymes ◽  
Content Type ◽  
Threonine Synthase ◽  
Homoserine Kinase ◽  
Exciting Potential ◽  
Feedback Inhibitor

ABSTRACT The fungally conserved subset of amino acid biosynthetic enzymes not present in humans offer exciting potential as an unexploited class of antifungal drug targets. Since threonine biosynthesis is essential in Cryptococcus neoformans, we further explored the potential of threonine biosynthetic enzymes as antifungal drug targets by determining the survival in mice of Saccharomyces cerevisiae homoserine kinase (thr1Δ) and threonine synthase (thr4Δ) mutants. In striking contrast to aspartate kinase (hom3Δ) mutants, S. cerevisiae thr1Δ and thr4Δ mutants were severely depleted after only 4 h in vivo. Similarly, Candida albicans thr1Δ mutants, but not hom3Δ mutants, were significantly attenuated in virulence. Consistent with the in vivo phenotypes, S. cerevisiae thr1Δ and thr4Δ mutants as well as C. albicans thr1Δ mutants were extremely serum sensitive. In both species, serum sensitivity was suppressed by the addition of threonine, a feedback inhibitor of Hom3p. Because mutation of the HOM3 and HOM6 genes, required for the production of the toxic pathway intermediate homoserine, also suppressed serum sensitivity, we hypothesize that serum sensitivity is a consequence of homoserine accumulation. Serum survival is critical for dissemination, an important virulence determinant: thus, together with the essential nature of C. neoformans threonine synthesis, the cross-species serum sensitivity of thr1Δ mutants makes the fungus-specific Thr1p, and likely Thr4p, ideal antifungal drug targets.

scholarly journals Trypanosoma brucei Pex13.2 Is an Accessory Peroxin That Functions in the Import of Peroxisome Targeting Sequence Type 2 Proteins and Localizes to Subdomains of the Glycosome

mSphere ◽  
2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Logan P. Crowe ◽  
Christina L. Wilkinson ◽  
Kathleen R. Nicholson ◽  
Meredith T. Morris
Keyword(s):  
Trypanosoma Brucei ◽  
Drug Targets ◽  
Protein Import ◽  
Specific Protein ◽  
Soluble Receptors ◽  
Two Dimensional Gel Electrophoresis ◽  
Content Type ◽  
Superresolution Microscopy

ABSTRACT Kinetoplastid parasites, including Trypanosoma brucei, Trypanosoma cruzi, and Leishmania, harbor unique organelles known as glycosomes, which are evolutionarily related to peroxisomes. Glycosome/peroxisome biogenesis is mediated by proteins called peroxins that facilitate organelle formation, proliferation, and degradation and import of proteins housed therein. Import of matrix proteins occurs via one of two pathways that are dictated by their peroxisome targeting sequence (PTS). In PTS1 import, a C-terminal tripeptide sequence, most commonly SKL, is recognized by the soluble receptor Pex5. In PTS2 import, a less conserved N-terminal sequence is recognized by Pex7. The soluble receptors deliver their cargo to the import channel consisting minimally of Pex13 and Pex14. While much of the import process is conserved, kinetoplastids are the only organisms to have two Pex13s, Pex13.1 and Pex13.2. It is unclear why trypanosomes require two Pex13s when one is sufficient for most eukaryotes. To interrogate the role of Pex13.2, we have employed biochemical approaches to partially resolve the composition of the Pex13/Pex14 import complexes in T. brucei and characterized glycosome morphology and protein import in Pex13.2-deficient parasites. Here, we show that Pex13.2 is an integral glycosome membrane protein that interacts with Pex13.1 and Pex14. The N terminus of Pex13.2 faces the cytoplasmic side of the membrane, where it can facilitate interactions required for protein import. Two-dimensional gel electrophoresis revealed three glycosome membrane complexes containing combinations of Pex13.1, Pex13.2, and Pex14. The silencing of Pex13.2 resulted in parasites with fewer, larger glycosomes and disrupted glycosome protein import, suggesting the protein is involved in glycosome biogenesis as well as protein import. Furthermore, superresolution microscopy demonstrated that Pex13.2 localizes to discrete foci in the glycosome periphery, indicating that the glycosome periphery is not homogenous. IMPORTANCE Trypanosoma brucei causes human African trypanosomiasis and a wasting disease called Nagana in livestock. Current treatments are expensive, toxic, and difficult to administer. Because of this, the search for new drug targets is essential. T. brucei has glycosomes that are essential to parasite survival; however, our ability to target them in drug development is hindered by our lack of understanding about how these organelles are formed and maintained. This work forwards our understanding of how the parasite-specific protein Pex13.2 functions in glycosome protein import and lays the foundation for future studies focused on blocking Pex13.2 function, which would be lethal to bloodstream-form parasites that reside in the mammalian bloodstream.

scholarly journals A Trypanosoma brucei ORFeome-Based Gain-of-Function Library Identifies Genes That Promote Survival during Melarsoprol Treatment

mSphere ◽  
2020 ◽  
Vol 5 (5) ◽  
Author(s):  
McKenzie Carter ◽  
Stephanie Gomez ◽  
Sam Gritz ◽  
Stephen Larson ◽  
Eugenia Silva-Herzog ◽  
...  
Keyword(s):  
Trypanosoma Brucei ◽  
Drug Targets ◽  
Large Scale ◽  
Resistance Mechanisms ◽  
Genetic Screen ◽  
Forward Genetics ◽  
Gain Of Function ◽  
Content Type ◽  
Genetic Tools ◽  
Gene Functions

ABSTRACT Trypanosoma brucei is an early branching protozoan parasite that causes human and animal African trypanosomiasis. Forward genetics approaches are powerful tools for uncovering novel aspects of trypanosomatid biology, pathogenesis, and therapeutic approaches against trypanosomiasis. Here, we have generated a T. brucei cloned ORFeome consisting of >90% of the targeted 7,245 genes and used it to make an inducible gain-of-function parasite library broadly applicable to large-scale forward genetic screens. We conducted a proof-of-principle genetic screen to identify genes whose expression promotes survival in melarsoprol, a critical drug of last resort. The 57 genes identified as overrepresented in melarsoprol survivor populations included the gene encoding the rate-limiting enzyme for the biosynthesis of an established drug target (trypanothione), validating the tool. In addition, novel genes associated with gene expression, flagellum localization, and mitochondrion localization were identified, and a subset of those genes increased melarsoprol resistance upon overexpression in culture. These findings offer new insights into trypanosomatid basic biology, implications for drug targets, and direct or indirect drug resistance mechanisms. This study generated a T. brucei ORFeome and gain-of-function parasite library, demonstrated the library’s usefulness in forward genetic screening, and identified novel aspects of melarsoprol resistance that will be the subject of future investigations. These powerful genetic tools can be used to broadly advance trypanosomatid research. IMPORTANCE Trypanosomatid parasites threaten the health of more than 1 billion people worldwide. Because their genomes are highly diverged from those of well-established eukaryotes, conservation is not always useful in assigning gene functions. However, it is precisely among the trypanosomatid-specific genes that ideal therapeutic targets might be found. Forward genetics approaches are an effective way to identify novel gene functions. We used an ORFeome approach to clone a large percentage of Trypanosoma brucei genes and generate a gain-of-function parasite library. This library was used in a genetic screen to identify genes that promote resistance to the clinically significant yet highly toxic drug melarsoprol. Hits arising from the screen demonstrated the library’s usefulness in identifying known pathways and uncovered novel aspects of resistance mediated by proteins localized to the flagellum and mitochondrion. The powerful new genetic tools generated herein are expected to promote advances in trypanosomatid biology and therapeutic development in the years to come.

scholarly journals Mutation ofRv2887, amarR-Like Gene, Confers Mycobacterium tuberculosis Resistance to an Imidazopyridine-Based Agent

2015 ◽  
Vol 59 (11) ◽  
pp. 6873-6881 ◽  
Author(s):  
Kathryn Winglee ◽  
Shichun Lun ◽  
Marco Pieroni ◽  
Alan Kozikowski ◽  
William Bishai
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Drug Targets ◽  
Efflux Pump ◽  
Transcriptional Regulator ◽  
Cross Resistance ◽  
Loss Of Function ◽  
Strong Activity ◽  
Content Type ◽  
Novel Drug

ABSTRACTDrug resistance is a major problem inMycobacterium tuberculosiscontrol, and it is critical to identify novel drug targets and new antimycobacterial compounds. We have previously identified an imidazo[1,2-a]pyridine-4-carbonitrile-based agent, MP-III-71, with strong activity againstM. tuberculosis. In this study, we evaluated mechanisms of resistance to MP-III-71. We derived three independentM. tuberculosismutants resistant to MP-III-71 and conducted whole-genome sequencing of these mutants. Loss-of-function mutations inRv2887were common to all three MP-III-71-resistant mutants, and we confirmed the role ofRv2887as a gene required for MP-III-71 susceptibility using complementation. The Rv2887 protein was previously unannotated, but domain and homology analyses suggested it to be a transcriptional regulator in the MarR (multiple antibiotic resistance repressor) family, a group of proteins first identified inEscherichia colito negatively regulate efflux pumps and other mechanisms of multidrug resistance. We found that two efflux pump inhibitors, verapamil and chlorpromazine, potentiate the action of MP-III-71 and that mutation ofRv2887abrogates their activity. We also used transcriptome sequencing (RNA-seq) to identify genes which are differentially expressed in the presence and absence of a functional Rv2887 protein. We found that genes involved in benzoquinone and menaquinone biosynthesis were repressed by functional Rv2887. Thus, inactivating mutations ofRv2887, encoding a putative MarR-like transcriptional regulator, confer resistance to MP-III-71, an effective antimycobacterial compound that shows no cross-resistance to existing antituberculosis drugs. The mechanism of resistance ofM. tuberculosisRv2887mutants may involve efflux pump upregulation and also drug methylation.

Cytosolic and mitochondrial Hsp90 in cytokinesis, mitochondrial DNA replication, and drug action in Trypanosoma brucei

2021 ◽  
Author(s):  
Kirsten J. Meyer ◽  
Theresa A. Shapiro
Keyword(s):  
Mitochondrial Dna ◽  
Trypanosoma Brucei ◽  
Cell Biology ◽  
Drug Targets ◽  
Heat Shock Protein 90 ◽  
Cell Cycle Regulators ◽  
Hsp90 Inhibitors ◽  
African Trypanosomes ◽  
Hsp90 Activity

Trypanosoma brucei subspecies cause African sleeping sickness in humans, an infection that is commonly fatal if not treated, and available therapies are limited. Previous studies have shown that heat shock protein 90 (Hsp90) inhibitors have potent and vivid activity against bloodstream form trypanosomes. Hsp90s are phylogenetically conserved and essential catalysts that function at the crux of cell biology, where they ensure the proper folding of proteins and their assembly into multicomponent complexes. To assess the specificity of Hsp90 inhibitors and further define the role of Hsp90s in African trypanosomes, we used RNAi to knockdown cytosolic and mitochondrial Hsp90s (HSP83 and HSP84, respectively). Loss of either protein led to cell death but the phenotypes were distinctly different. Depletion of cytosolic HSP83 closely mimicked the consequences of chemically depleting Hsp90 activity with inhibitor 17-AAG. In these cells cytokinesis was severely disrupted and segregation of the kinetoplast (the massive mitochondrial DNA structure unique to this family of eukaryotic pathogens) was impaired, leading to cells with abnormal kDNA structures. Quite differently, knockdown of mitochondrial HSP84 did not impair cytokinesis but halted the initiation of new kDNA synthesis, generating cells without kDNA. These findings highlight the central role for Hsp90s in chaperoning cell cycle regulators in trypanosomes, reveal their unique function in kinetoplast replication, and reinforce their specificity and value as drug targets.

scholarly journals The Nuclear Export Receptors TbMex67 and TbMtr2 Are Required for Ribosome Biogenesis in Trypanosoma brucei

mSphere ◽  
2019 ◽  
Vol 4 (4) ◽  
Author(s):  
Constance Rink ◽  
Martin Ciganda ◽  
Noreen Williams
Keyword(s):  
Trypanosoma Brucei ◽  
Nuclear Export ◽  
Ribosome Biogenesis ◽  
Biological Process ◽  
Large Subunit ◽  
Critical Role ◽  
Ribosomal Subunits ◽  
Content Type ◽  
Protein Components ◽  
Export Receptors

ABSTRACT Ribosomal maturation is a complex and highly conserved biological process involving migration of a continuously changing RNP across multiple cellular compartments. A critical point in this process is the translocation of individual ribosomal subunits (60S and 40S) from the nucleus to the cytoplasm, and a number of export factors participate in this process. In this study, we characterize the functional role of the auxiliary export receptors TbMex67 and TbMtr2 in ribosome biogenesis in the parasite Trypanosoma brucei. We demonstrate that depletion of each of these proteins dramatically impacts the steady-state levels of other proteins involved in ribosome biogenesis, including the trypanosome-specific factors P34 and P37. In addition, we observe that the loss of TbMex67 or TbMtr2 leads to aberrant ribosome formation, rRNA processing, and polysome formation. Although the TbMex67-TbMtr2 heterodimer is structurally distinct from Mex67-Mtr2 complexes previously studied, our data show that they retain a conserved function in ribosome biogenesis. IMPORTANCE The nuclear export of ribosomal subunits (60S and 40S) depends in part on the activity of the essential auxiliary export receptors TbMtr2 and TbMex67. When these proteins are individually depleted from the medically and agriculturally significant parasite Trypanosoma brucei, distinct alterations in the processing of the rRNAs of the large subunit (60S) are observed as well as aberrations in the assembly of functional ribosomes (polysomes). We also established that TbMex67 and TbMtr2 interact directly or indirectly with the protein components of the 5S RNP, including the trypanosome-specific P34/P37. The critical role that TbMex67 and TbMtr2 play in this essential biological process together with their parasite-specific interactions may provide new therapeutic targets against this important parasite.

scholarly journals A Chemical Rescue Screen Identifies a Plasmodium falciparum Apicoplast Inhibitor Targeting MEP Isoprenoid Precursor Biosynthesis

2014 ◽  
Vol 59 (1) ◽  
pp. 356-364 ◽  
Author(s):  
Wesley Wu ◽  
Zachary Herrera ◽  
Danny Ebert ◽  
Katie Baska ◽  
Seok H. Cho ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Antimalarial Drug ◽  
Drug Targets ◽  
Specific Activity ◽  
Drug Candidate ◽  
Content Type ◽  
Chemical Rescue ◽  
Growth Inhibitory ◽  
Parasite Populations

ABSTRACTThe apicoplast is an essential plastid organelle found inPlasmodiumparasites which contains several clinically validated antimalarial-drug targets. A chemical rescue screen identified MMV-08138 from the “Malaria Box” library of growth-inhibitory antimalarial compounds as having specific activity against the apicoplast. MMV-08138 inhibition of blood-stagePlasmodium falciparumgrowth is stereospecific and potent, with the most active diastereomer demonstrating a 50% effective concentration (EC50) of 110 nM. Whole-genome sequencing of 3 drug-resistant parasite populations from two independent selections revealed E688Q and L244I mutations inP. falciparumIspD, an enzyme in the MEP (methyl-d-erythritol-4-phosphate) isoprenoid precursor biosynthesis pathway in the apicoplast. The active diastereomer of MMV-08138 directly inhibited PfIspD activityin vitrowith a 50% inhibitory concentration (IC50) of 7.0 nM. MMV-08138 is the first PfIspD inhibitor to be identified and, together with heterologously expressed PfIspD, provides the foundation for further development of this promising antimalarial drug candidate lead. Furthermore, this report validates the use of the apicoplast chemical rescue screen coupled with target elucidation as a discovery tool to identify specific apicoplast-targeting compounds with new mechanisms of action.

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