GPI-anchored proteins and free GPI glycolipids of procyclic form Trypanosoma brucei are nonessential for growth, are required for colonization of the tsetse fly, and are not the only components of the surface coat

Transcriptome profiles of Trypanosoma brucei rhodesiense in Malawi reveal focus specific gene expression profiles associated with pathology

BACKGROUND

Sleeping sickness caused by Trypanosoma brucei rhodesiense is a fatal disease and endemic in Southern and Eastern Africa. There is an urgent need to develop novel diagnostic and control tools to achieve elimination of rhodesiense sleeping sickness which might be achieved through a better understanding of trypanosome gene expression and genetics using endemic isolates. Here, we describe transcriptome profiles and population structure of endemic T. b. rhodesiense isolates in human blood in Malawi.

METHODOLOGY

Blood samples of r-HAT cases from Nkhotakota and Rumphi foci were collected in PaxGene tubes for RNA extraction before initiation of r-HAT treatment. 100 million reads were obtained per sample, reads were initially mapped to the human genome reference GRCh38 using HiSat2 and then the unmapped reads were mapped against Trypanosoma brucei reference transcriptome (TriTrypDB54_TbruceiTREU927) using HiSat2. Differential gene expression analysis was done using the DeSeq2 package in R. SNP calling from reads that were mapped to the T. brucei genome was done using GATK in order to identify T.b. rhodesiense population structure.

RESULTS

24 samples were collected from r-HAT cases of which 8 were from Rumphi and 16 from Nkhotakota foci. The isolates from Nkhotakota were enriched with transcripts for cell cycle arrest and stumpy form markers, whereas isolates in Rumphi focus were enriched with transcripts for folate biosynthesis and antigenic variation pathways. These parasite focus-specific transcriptome profiles are consistent with the more virulent disease observed in Rumphi and a less symptomatic disease in Nkhotakota associated with the non-dividing stumpy form. Interestingly, the Malawi T.b. rhodesiense isolates expressed genes enriched for reduced cell proliferation compared to the Uganda T.b. rhodesiense isolates. PCA analysis using SNPs called from the RNAseq data showed that T. b. rhodesiense parasites from Nkhotakota are genetically distinct from those collected in Rumphi.

CONCLUSION

Our results suggest that the differences in disease presentation in the two foci is mainly driven by genetic differences in the parasites in the two major endemic foci of Rumphi and Nkhotakota rather than differences in the environment or host response.

Ancestral aneuploidy and stable chromosomal duplication resulting in differential genome structure and gene expression control in trypanosomatid parasites

Aneuploidy is widely observed in both unicellular and multicellular eukaryotes, usually associated with adaptation to stress conditions. Chromosomal duplication stability is a tradeoff between the fitness cost of having unbalanced gene copies and the potential fitness gained from increased dosage of specific advantageous genes. Trypanosomatids, a family of protozoans that include species that cause neglected tropical diseases, are a relevant group to study aneuploidies. Their life cycle has several stressors that could select for different patterns of chromosomal duplications and/or losses, and their nearly universal use of polycistronic transcription increases their reliance on gene expansion/contraction, as well as post-transcriptional control as mechanisms for gene expression regulation. By evaluating the data from 866 isolates covering seven trypanosomatid genera, we have revealed that aneuploidy tolerance is an ancestral characteristic of trypanosomatids but has a reduced occurrence in a specific monophyletic clade that has undergone large genomic reorganization and chromosomal fusions. We have also identified an ancient chromosomal duplication that was maintained across these parasite's speciation, named collectively as the trypanosomatid ancestral supernumerary chromosome (TASC). TASC has most genes in the same coding strand, is expressed as a disomic chromosome (even having four copies), and has increased potential for functional variation, but it purges highly deleterious mutations more efficiently than other chromosomes. The evidence of stringent control over gene expression in this chromosome suggests that these parasites have adapted to mitigate the fitness cost associated with this ancient chromosomal duplication.

Anthelmintic efficacy evaluation and mechanism of N-methylbenzo[d]oxazol-2-amine

Parasitic roundworms cause significant sickness and mortality in animals and humans. In livestock, these nematodes have severe economic impact and result in losses in food production on a global scale. None of the currently available drugs ideally suit all treatment circumstances, and the development of drug-resistant nematode strains has become a challenge to control the infection. There is an urgent need to develop novel anthelmintic compounds. According to our previous report, N-methylbenzo[d]oxazol-2-amine (1) showed anthelmintic activity and lowest cytotoxicity. In this study, in vivo anthelmintic properties were evaluated using Trichinella spiralis infected mice. Toxicity was evaluated using the rats and mode of action using molecular docking and metabolomics approaches. The in vivo results demonstrate that a dose of 250 mg/kg reduced the T. spiralis abundance in the digestive tract by 49%. The 250 mg/kg Albendazole was served as control. The relatively low acute toxicity was categorized into chemical category 5, with an LD50 greater than 2000 mg/kg body. Molecular docking analysis showed the T. spiralis tubulin beta chain and glutamate-gated channels might not be the main targets of compound 1. Metabolomics analysis was used to explain the effects of compound 1 on the T. spiralis adult worm. The results demonstrated that compound 1 significantly up-regulated the metabolism of purine, pyrimidine and down-regulated sphingolipid metabolism. In conclusion, compound 1 could be a potential molecule for anthelmintic development. The bioavailability, pharmacokinetics, and absorption of this compound should be studied further to provide information for its future efficacy improvement.

Identification of the glycosylphosphatidylinositol-specific phospholipase A2 (GPI-PLA2) that mediates GPI fatty acid remodeling in Trypanosoma brucei

The biosynthesis of glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) in the parasitic protozoan Trypanosoma brucei involves fatty acid remodeling of the GPI precursor molecules before they are transferred to protein in the endoplasmic reticulum. The genes encoding the requisite phospholipase A2 and A1 activities for this remodeling have thus far been elusive. Here, we identify a gene, Tb927.7.6110, that encodes a protein that is both necessary and sufficient for GPI-phospholipase A2 (GPI-PLA2) activity in the procyclic form of the parasite. The predicted protein product belongs to the alkaline ceramidase, PAQR receptor, Per1, SID-1, and TMEM8 (CREST) superfamily of transmembrane hydrolase proteins and shows sequence similarity to Post-GPI-Attachment to Protein 6 (PGAP6), a GPI-PLA2 that acts after transfer of GPI precursors to protein in mammalian cells. We show the trypanosome Tb927.7.6110 GPI-PLA2 gene resides in a locus with two closely related genes Tb927.7.6150 and Tb927.7.6170, one of which (Tb927.7.6150) most likely encodes a catalytically inactive protein. The absence of GPI-PLA2 in the null mutant procyclic cells not only affected fatty acid remodeling but also reduced GPI anchor sidechain size on mature GPI-anchored procyclin glycoproteins. This reduction in GPI anchor sidechain size was reversed upon the re-addition of Tb927.7.6110 and of Tb927.7.6170, despite the latter not encoding GPI precursor GPI-PLA2 activity. Taken together, we conclude that Tb927.7.6110 encodes the GPI-PLA2 of GPI precursor fatty acid remodeling and that more work is required to assess the roles and essentiality of Tb927.7.6170 and the presumably enzymatically inactive Tb927.7.6150.

Fatty acid uptake in Trypanosoma brucei: Host resources and possible mechanisms

Trypanosoma brucei spp. causes African Sleeping Sickness in humans and nagana, a wasting disease, in cattle. As T. brucei goes through its life cycle in its mammalian and insect vector hosts, it is exposed to distinct environments that differ in their nutrient resources. One such nutrient resource is fatty acids, which T. brucei uses to build complex lipids or as a potential carbon source for oxidative metabolism. Of note, fatty acids are the membrane anchoring moiety of the glycosylphosphatidylinositol (GPI)-anchors of the major surface proteins, Variant Surface Glycoprotein (VSG) and the Procyclins, which are implicated in parasite survival in the host. While T. brucei can synthesize fatty acids de novo, it also readily acquires fatty acids from its surroundings. The relative contribution of parasite-derived vs. host-derived fatty acids to T. brucei growth and survival is not known, nor have the molecular mechanisms of fatty acid uptake been defined. To facilitate experimental inquiry into these important aspects of T. brucei biology, we addressed two questions in this review: (1) What is known about the availability of fatty acids in different host tissues where T. brucei can live? (2) What is known about the molecular mechanisms mediating fatty acid uptake in T. brucei? Finally, based on existing biochemical and genomic data, we suggest a model for T. brucei fatty acid uptake that proposes two major routes of fatty acid uptake: diffusion across membranes followed by intracellular trapping, and endocytosis of host lipoproteins.

Common and unique features of glycosylation and glycosyltransferases in African trypanosomes

Eukaryotic protein glycosylation is mediated by glycosyl- and oligosaccharyl-transferases. Here, we describe how African trypanosomes exhibit both evolutionary conservation and significant divergence compared with other eukaryotes in how they synthesise their glycoproteins. The kinetoplastid parasites have conserved components of the dolichol-cycle and oligosaccharyltransferases (OSTs) of protein N-glycosylation, and of glycosylphosphatidylinositol (GPI) anchor biosynthesis and transfer to protein. However, some components are missing, and they process and decorate their N-glycans and GPI anchors in unique ways. To do so, they appear to have evolved a distinct and functionally flexible glycosyltransferases (GT) family, the GT67 family, from an ancestral eukaryotic β3GT gene. The expansion and/or loss of GT67 genes appears to be dependent on parasite biology. Some appear to correlate with the obligate passage of parasites through an insect vector, suggesting they were acquired through GT67 gene expansion to assist insect vector (tsetse fly) colonisation. Others appear to have been lost in species that subsequently adopted contaminative transmission. We also highlight the recent discovery of a novel and essential GT11 family of kinetoplastid parasite fucosyltransferases that are uniquely localised to the mitochondria of Trypanosoma brucei and Leishmania major. The origins of these kinetoplastid FUT1 genes, and additional putative mitochondrial GT genes, are discussed.

The Leishmania donovani Ortholog of the Glycosylphosphatidylinositol Anchor Biosynthesis Cofactor PBN1 Is Essential for Host Infection

Visceral leishmaniasis is a deadly infectious disease caused by Leishmania donovani, a kinetoplastid parasite for which no licensed vaccine is available. To identify potential vaccine candidates, we systematically identified genes encoding putative cell surface and secreted proteins essential for parasite viability and host infection. We identified a protein encoded by LdBPK_061160 which, when ablated, resulted in a remarkable increase in parasite adhesion to tissue culture flasks. Here, we show that this phenotype is caused by the loss of glycosylphosphatidylinositol (GPI)-anchored surface molecules and that LdBPK_061160 encodes a noncatalytic component of the L. donovani GPI-mannosyltransferase I (GPI-MT I) complex. GPI-anchored surface molecules were rescued in the LdBPK_061160 mutant by the ectopic expression of both human genes PIG-X and PIG-M, but neither gene could complement the phenotype alone. From further sequence comparisons, we conclude that LdBPK_061160 is the functional orthologue of yeast PBN1 and mammalian PIG-X, which encode the noncatalytic subunits of their respective GPI-MT I complexes, and we assign LdBPK_061160 as LdPBN1. The LdPBN1 mutants could not establish a visceral infection in mice, a phenotype that was rescued by constitutive expression of LdPBN1. Although mice infected with the null mutant did not develop an infection, exposure to these parasites provided significant protection against subsequent infection with a virulent strain. In summary, we have identified the orthologue of the PBN1/PIG-X noncatalytic subunit of GPI-MT I in trypanosomatids, shown that it is essential for infection in a murine model of visceral leishmaniasis, and demonstrated that the LdPBN1 mutant shows promise for the development of an attenuated live vaccine.

Visualisation of experimentally determined and predicted protein N-glycosylation and predicted glycosylphosphatidylinositol anchor addition in Trypanosoma brucei

Background: Trypanosoma brucei is a protozoan parasite and the etiological agent of human and animal African trypanosomiasis. The organism cycles between its mammalian host and tsetse vector. The host-dwelling bloodstream form of the parasite is covered with a monolayer of variant surface glycoprotein (VSG) that enables it to escape both the innate and adaptive immune systems. Within this coat reside lower-abundance surface glycoproteins that function as receptors and/or nutrient transporters. The glycosylation of the Trypanosoma brucei surface proteome is essential to evade the immune response and is mediated by three oligosaccharyltransferase genes; two of which, TbSTT3A and TbSTT3B, are expressed in the bloodstream form of the parasite.

Methods: We processed a recent dataset of our laboratory to visualise putative glycosylation sites of the Trypanosoma brucei proteome. We provided a visualisation for the predictions of glycosylation carried by TbSTT3A and TbSTT3B, and we augmented the visualisation with predictions for Glycosylphosphatidylinositol anchoring sites, domains and topology of the Trypanosoma brucei proteome.

Conclusions: We created a web service to explore the glycosylation sites of the Trypanosoma brucei oligosaccharyltransferases substrates, using data described in a recent publication of our laboratory. We also made a machine learning algorithm available as a web service, described in our recent publication, to distinguish between TbSTT3A and TbSTT3B substrates.

Persistence of Trypanosoma brucei as early procyclic forms and social motility are dependent on glycosylphosphatidylinositol transamidase

Glycosylphosphatidylinositol (GPI)‐linked molecules are surface‐exposed membrane components that influence the infectivity, virulence and transmission of many eukaryotic pathogens. Procyclic (insect midgut) forms of Trypanosoma brucei do not require GPI‐anchored proteins for growth in suspension culture. Deletion of TbGPI8, and inactivation of the GPI:protein transamidase complex, is tolerated by cultured procyclic forms. Using a conditional knockout, we show TbGPI8 is required for social motility (SoMo). This collective migration by cultured early procyclic forms has been linked to colonization of the tsetse fly digestive tract. The SoMo‐negative phenotype was observed after a lag phase with respect to loss of TbGPI8 and correlated with an unexpectedly slow loss of procyclins, the major GPI‐anchored proteins. Procyclins are not essential for SoMo, however, suggesting a requirement for at least one other GPI‐anchored protein. Loss of TbGPI8 initiates the transition from early to late procyclic forms; this effect was observed in a subpopulation in suspension culture, and was more pronounced when cells were cultured on SoMo plates. Our results indicate two, potentially interlinked, scenarios that may explain the previously reported failure of TbGPI8 deletion mutants to establish a midgut infection in the tsetse fly: interference with stage‐specific gene expression and absence of SoMo.

An essential, kinetoplastid-specific GDP-Fuc: β-D-Gal α-1,2-fucosyltransferase is located in the mitochondrion of Trypanosoma brucei

Fucose is a common component of eukaryotic cell-surface glycoconjugates, generally added by Golgi-resident fucosyltransferases. Whereas fucosylated glycoconjugates are rare in kinetoplastids, the biosynthesis of the nucleotide sugar GDP-Fuc has been shown to be essential in Trypanosoma brucei. Here we show that the single identifiable T. brucei fucosyltransferase (TbFUT1) is a GDP-Fuc: β-D-galactose α-1,2-fucosyltransferase with an apparent preference for a Galβ1,3GlcNAcβ1-O-R acceptor motif. Conditional null mutants of TbFUT1 demonstrated that it is essential for both the mammalian-infective bloodstream form and the insect vector-dwelling procyclic form. Unexpectedly, TbFUT1 was localized in the mitochondrion of T. brucei and found to be required for mitochondrial function in bloodstream form trypanosomes. Finally, the TbFUT1 gene was able to complement a Leishmania major mutant lacking the homologous fucosyltransferase gene (Guo et al., 2021). Together these results suggest that kinetoplastids possess an unusual, conserved and essential mitochondrial fucosyltransferase activity that may have therapeutic potential across trypanosomatids.

Elimination of GPI2 suppresses glycosylphosphatidylinositol GlcNAc transferase activity and alters GPI glycan modification in Trypanosoma brucei

Many eukaryotic cell-surface proteins are post-translationally modified by a glycosylphosphatidylinositol (GPI) moiety that anchors them to the cell membrane. The biosynthesis of GPI anchors is initiated in the endoplasmic reticulum by transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol. This reaction is catalyzed by GPI GlcNAc transferase, a multisubunit complex comprising the catalytic subunit Gpi3/PIG-A as well as at least five other subunits, including the hydrophobic protein Gpi2, which is essential for the activity of the complex in yeast and mammals, but the function of which is not known. To investigate the role of Gpi2, we exploited Trypanosoma brucei (Tb), an early diverging eukaryote and important model organism that initially provided the first insights into GPI structure and biosynthesis. We generated insect-stage (procyclic) trypanosomes that lack TbGPI2 and found that in TbGPI2-null parasites, (i) GPI GlcNAc transferase activity is reduced, but not lost, in contrast with yeast and human cells, (ii) the GPI GlcNAc transferase complex persists, but its architecture is affected, with loss of at least the TbGPI1 subunit, and (iii) the GPI anchors of procyclins, the major surface proteins, are underglycosylated when compared with their WT counterparts, indicating the importance of TbGPI2 for reactions that occur in the Golgi apparatus. Immunofluorescence microscopy localized TbGPI2 not only to the endoplasmic reticulum but also to the Golgi apparatus, suggesting that in addition to its expected function as a subunit of the GPI GlcNAc transferase complex, TbGPI2 may have an enigmatic noncanonical role in Golgi-localized GPI anchor modification in trypanosomes.

Nucleotide sugar biosynthesis occurs in the glycosomes of procyclic and bloodstream form Trypanosoma brucei

In Trypanosoma brucei, there are fourteen enzymatic biotransformations that collectively convert glucose into five essential nucleotide sugars: UDP-Glc, UDP-Gal, UDP-GlcNAc, GDP-Man and GDP-Fuc. These biotransformations are catalyzed by thirteen discrete enzymes, five of which possess putative peroxisome targeting sequences. Published experimental analyses using immunofluorescence microscopy and/or digitonin latency and/or subcellular fractionation and/or organelle proteomics have localized eight and six of these enzymes to the glycosomes of bloodstream form and procyclic form T. brucei, respectively. Here we increase these glycosome localizations to eleven in both lifecycle stages while noting that one, phospho-N-acetylglucosamine mutase, also localizes to the cytoplasm. In the course of these studies, the heterogeneity of glycosome contents was also noted. These data suggest that, unlike other eukaryotes, all of nucleotide sugar biosynthesis in T. brucei is compartmentalized to the glycosomes in both lifecycle stages. The implications are discussed.

Complexity of the eukaryotic dolichol-linked oligosaccharide scramblase suggested by activity correlation profiling mass spectrometry

The oligosaccharide required for asparagine (N)-linked glycosylation of proteins in the endoplasmic reticulum (ER) is donated by the glycolipid Glc₃Man₉GlcNAc₂-PP-dolichol. Remarkably, whereas glycosylation occurs in the ER lumen, the initial steps of Glc₃Man₉GlcNAc₂-PP-dolichol synthesis generate the lipid intermediate Man₅GlcNAc₂-PP-dolichol (M5-DLO) on the cytoplasmic side of the ER. Glycolipid assembly is completed only after M5-DLO is translocated to the luminal side. The membrane protein (M5-DLO scramblase) that mediates M5-DLO translocation across the ER membrane has not been identified, despite its importance for N-glycosylation. Building on our ability to recapitulate scramblase activity in proteoliposomes reconstituted with a crude mixture of ER membrane proteins, we developed a mass spectrometry-based 'activity correlation profiling' approach to identify scramblase candidates in the yeast Saccharomyces cerevisiae. Data curation prioritized six polytopic ER membrane proteins as scramblase candidates, but reconstitution-based assays and gene disruption in the protist Trypanosoma brucei revealed, unexpectedly, that none of these proteins is necessary for M5-DLO scramblase activity. Our results instead strongly suggest that M5-DLO scramblase activity is due to a protein, or protein complex, whose activity is regulated at the level of quaternary structure.

Discovery and Genetic Validation of Chemotherapeutic Targets for Chagas' Disease

There is an urgent need to develop new treatments for Chagas' disease. To identify drug targets, it is important to understand the basic biology of Trypanosoma cruzi, in particular with respect to the biological pathways or proteins that are essential for its survival within the host. This review provides a streamlined approach for identifying drug targets using freely available chemogenetic databases and outlines the relevant characteristics of an ideal chemotherapeutic target. Among those are their essentiality, druggability, availability of structural information, and selectivity. At the moment only 16 genes have been found as essential by gene disruption in T. cruzi. At the TDR Targets database, a chemogenomics resource for neglected diseases, information about published structures for these genes was only found for three of these genes, and annotation of validated inhibitors was found in two. These inhibitors have activity against the parasitic stages present in the host. We then analyzed three of the pathways that are considered promising in the search for new targets: (1) Ergosterol biosynthesis, (2) Resistance to oxidative stress, (3) Synthesis of surface glycoconjugates. We have annotated all the genes that participate in them, identified those that are considered as druggable, and incorporated evidence from either Trypanosoma brucei, and Leishmania spp. that supports the hypothesis that these pathways are essential for T. cruzi survival.

O-Fucosylation of thrombospondin-like repeats is required for processing of microneme protein 2 and for efficient host cell invasion by Toxoplasma gondii tachyzoites

Toxoplasma gondii is an intracellular parasite that causes disseminated infections that can produce neurological damage in fetuses and immunocompromised individuals. Microneme protein 2 (MIC2), a member of the thrombospondin-related anonymous protein (TRAP) family, is a secreted protein important for T. gondii motility, host cell attachment, invasion, and egress. MIC2 contains six thrombospondin type I repeats (TSRs) that are modified by C-mannose and O-fucose in Plasmodium spp. and mammals. Here, using MS analysis, we found that the four TSRs in T. gondii MIC2 with protein O-fucosyltransferase 2 (POFUT2) acceptor sites are modified by a dHexHex disaccharide, whereas Trp residues within three TSRs are also modified with C-mannose. Disruption of genes encoding either POFUT2 or the putative GDP-fucose transporter (NST2) resulted in loss of MIC2 O-fucosylation, as detected by an antibody against the GlcFuc disaccharide, and in markedly reduced cellular levels of MIC2. Furthermore, in 10-15% of the Δpofut2 or Δnst2 vacuoles, MIC2 accumulated earlier in the secretory pathway rather than localizing to micronemes. Dissemination of tachyzoites in human foreskin fibroblasts was reduced for these knockouts, which both exhibited defects in attachment to and invasion of host cells comparable with the Δmic2 phenotype. These results, indicating that O-fucosylation of TSRs is required for efficient processing of MIC2 and for normal parasite invasion, are consistent with the recent demonstration that Plasmodium falciparum Δpofut2 strain has decreased virulence and also support a conserved role for this glycosylation pathway in quality control of TSR-containing proteins in eukaryotes.

The mRNA cap methyltransferase gene TbCMT1 is not essential in vitro but is a virulence factor in vivo for bloodstream form Trypanosoma brucei

Messenger RNA is modified by the addition of a 5' methylated cap structure, which protects the transcript and recruits protein complexes that mediate RNA processing and/or the initiation of translation. Two genes encoding mRNA cap methyltransferases have been identified in T. brucei: TbCMT1 and TbCGM1. Here we analysed the impact of TbCMT1 gene deletion on bloodstream form T. brucei cells. TbCMT1 was dispensable for parasite proliferation in in vitro culture. However, significantly decreased parasitemia was observed in mice inoculated with TbCMT1 null and conditional null cell lines. Using RNA-Seq, we observed that several cysteine peptidase mRNAs were downregulated in TbCMT1 null cells lines. The cysteine peptidase Cathepsin-L was also shown to be reduced at the protein level in TbCMT1 null cell lines. Our data suggest that TbCMT1 is not essential to bloodstream form T. brucei growth in vitro or in vivo but that it contributes significantly to parasite virulence in vivo.

UDP-glycosyltransferase genes in trypanosomatid genomes have diversified independently to meet the distinct developmental needs of parasite adaptations

BACKGROUND

Trypanosomatid parasites such as Trypanosoma spp. and Leishmania spp. are a major source of infectious disease in humans and domestic animals worldwide. Fundamental to the host-parasite interactions of these potent pathogens are their cell surfaces, which are highly decorated with glycosylated proteins and other macromolecules. Trypanosomatid genomes contain large multi-copy gene families encoding UDP-dependent glycosyltransferases (UGTs), the primary role of which is cell-surface decoration. Here we report a phylogenetic analysis of UGTs from diverse trypanosomatid genomes, the aim of which was to understand the origin and evolution of their diversity.

RESULTS

By combining phylogenetics with analyses of recombination, and selection, we compared UGT repertoire, genomic context and sequence evolution across 19 trypanosomatids. We identified a UGT lineage present in stercorarian trypanosomes and a free-living kinetoplastid Bodo saltans that likely represents the ancestral state of this gene family. The phylogeny of parasite-specific genes shows that UGTs repertoire in Leishmaniinae and salivarian trypanosomes has expanded independently and with distinct evolutionary dynamics. In the former, the ancestral UGT repertoire was organised in a tandem array from which sporadic transpositions to telomeric regions occurred, allowing expansion most likely through telomeric exchange. In the latter, the ancestral UGT repertoire was comprised of seven subtelomeric lineages, two of which have greatly expanded potentially by gene transposition between these dynamic regions of the genome.

CONCLUSIONS

The phylogeny of UGTs confirms that they represent a substantial parasite-specific innovation, which has diversified independently in the distinct trypanosomatid lineages. Nonetheless, developmental regulation has been a strong driver of UGTs diversification in both African trypanosomes and Leishmania.

Single-subunit oligosaccharyltransferases of Trypanosoma brucei display different and predictable peptide acceptor specificities

Trypanosoma brucei causes African trypanosomiasis and contains three full-length oligosaccharyltransferase (OST) genes; two of which, TbSTT3A and TbSTT3B, are expressed in the bloodstream form of the parasite. These OSTs have different peptide acceptor and lipid-linked oligosaccharide donor specificities, and trypanosomes do not follow many of the canonical rules developed for other eukaryotic N-glycosylation pathways, raising questions as to the basic architecture and detailed function of trypanosome OSTs. Here, we show by blue-native gel electrophoresis and stable isotope labeling in cell culture proteomics that the TbSTT3A and TbSTT3B proteins associate with each other in large complexes that contain no other detectable protein subunits. We probed the peptide acceptor specificities of the OSTs in vivo using a transgenic glycoprotein reporter system and performed glycoproteomics on endogenous parasite glycoproteins using sequential endoglycosidase H and peptide:N-glycosidase-F digestions. This allowed us to assess the relative occupancies of numerous N-glycosylation sites by endoglycosidase H-resistant N-glycans originating from Man5GlcNAc2-PP-dolichol transferred by TbSTT3A, and endoglycosidase H-sensitive N-glycans originating from Man9GlcNAc2-PP-dolichol transferred by TbSTT3B. Using machine learning, we assessed the features that best define TbSTT3A and TbSTT3B substrates in vivo and built an algorithm to predict the types of N-glycan most likely to predominate at all the putative N-glycosylation sites in the parasite proteome. Finally, molecular modeling was used to suggest why TbSTT3A has a distinct preference for sequons containing and/or flanked by acidic amino acid residues. Together, these studies provide insights into how a highly divergent eukaryote has re-wired protein N-glycosylation to provide protein sequence-specific N-glycan modifications. Data are available via ProteomeXchange with identifiers PXD007236, PXD007267, and PXD007268.

Leishmania (Viannia) braziliensis Inositol Phosphorylceramide: Distinctive Sphingoid Base Composition

Inositol phosphorylceramide (IPC), the major sphingolipid in the genus Leishmania but not found in mammals, is considered a potentially useful target for chemotherapy against leishmaniasis. Leishmania (Viannia) braziliensis is endemic in Latin America and causes American tegumentary leishmaniasis. We demonstrated that IPCs are localized internally in parasites, using a specific monoclonal antibody. Treatment with 5 μM myriocin (a serine palmitoyltransferase inhibitor) rendered promastigotes 8-fold less infective than controls in experimental hamster infection, as determined by number of parasites per inguinal lymph node after 8 weeks infection, suggesting the importance of parasite IPC or sphingolipid derivatives in parasite infectivity or survival in the host. IPC was isolated from promastigotes of three L. (V.) braziliensis strains and analyzed by positive- and negative-ion ESI-MS. The major IPC ions were characterized as eicosasphinganine and eicosasphingosine. Negative-ion ESI-MS revealed IPC ion species at m/z 778.6 (d20:1/14:0), 780.6 (d20:0/14:0), 796.6 (t20:0/14:0), 806.6 (d20:1/16:0), and 808.6 (d20:0/16:0). IPCs isolated from L. (V.) braziliensis and L. (L.) major showed significant differences in IPC ceramide composition. The major IPC ion from L. (L.) major, detected in negative-ion ESI-MS at m/z 780.6, was composed of ceramide d16:1/18:0. Our results suggest that sphingosine synthase (also known as serine palmitoyltransferase; SPT) in L. (V.) braziliensis is responsible for synthesis of a long-chain base of 20 carbons (d20), whereas SPT in L. (L.) major synthesizes a 16-carbon long-chain base (d16). A phylogenetic tree based on SPT proteins was constructed by analysis of sequence homologies in species of the Leishmania and Viannia subgenera. Results indicate that SPT gene position in L. (V.) braziliensis is completely separated from that of members of subgenus Leishmania, including L. (L.) major, L. (L.) infantum, and L. (L.) mexicana. Our findings clearly demonstrate sphingoid base differences between L. (V.) braziliensis and members of subgenus Leishmania, and are relevant to future development of more effective targeted anti-leishmaniasis drugs.

Lipidomics and anti-trypanosomatid chemotherapy

BACKGROUND

Trypanosomatids such as Leishmania, Trypanosoma brucei and Trypanosoma cruzi belong to the order Kinetoplastida and are the source of many significant human and animal diseases. Current treatment is unsatisfactory and is compromised by the rising appearance of drug resistant parasites. Novel and more effective chemotherapeutics are urgently needed to treat and prevent these devastating diseases, which relies on the identification of essential, parasite specific targets that are absent in the host. Lipids constitute essential components of the cell and carry out multiple critical functions from building blocks of biological membranes to regulatory roles in signal transduction, organellar biogenesis, energy storage, and virulence. The recent technological advances of lipidomics has facilitated the broadening of our knowledge in the field of cellular lipid content, structure, functions, and metabolic pathways.

MAIN BODY

This review highlights the application of lipidomics (i) in the characterization of the lipidome of kinetoplastid parasites or of their subcellular structure(s), (ii) in the identification of unique lipid species or metabolic pathways that can be targeted for novel drug therapies, (iii) as an analytic tool to gain a deeper insight into the roles of specific enzymes in lipid metabolism using genetically modified microorganisms, and (iv) in deciphering the mechanism of action of anti-microbial drugs on lipid metabolism. Lastly, an outlook stating where the field is evolving is presented.

CONCLUSION

Lipidomics has contributed to the expanding knowledge related to lipid metabolism, mechanism of drug action and resistance, and pathogen-host interaction of trypanosomatids, which provides a solid basis for the development of better anti-parasitic pharmaceuticals.

Molecular docking and molecular dynamics simulation study of inositol phosphorylceramide synthase - inhibitor complex in leishmaniasis: Insight into the structure based drug design

Inositol phosphorylceramide synthase (IPCS) has emerged as an important, interesting and attractive target in the sphingolipid metabolism of Leishmania. IPCS catalyzes the conversion of ceramide to IPC which forms the most predominant sphingolipid in Leishmania. IPCS has no mammalian equivalent and also plays an important role in maintaining the infectivity and viability of the parasite. The present study explores the possibility of targeting IPCS; development of suitable inhibitors for the same would serve as a treatment strategy for the infectious disease leishmaniasis. Five coumarin derivatives were developed as inhibitors of IPCS protein. Molecular dynamics simulations of the complexes of IPCS with these inhibitors were performed which provided insights into the binding modes of the inhibitors. In vitro screening of the top three compounds has resulted in the identification of one of the compounds (compound 3) which shows little cytotoxic effects. This compound therefore represents a good starting point for further in vivo experimentation and could possibly serve as an important drug candidate for the treatment of leishmaniasis.

Molecular docking and molecular dynamics simulation study of inositol phosphorylceramide synthase - inhibitor complex in leishmaniasis: Insight into the structure based drug design

Inositol phosphorylceramide synthase (IPCS) has emerged as an important, interesting and attractive target in the sphingolipid metabolism of Leishmania. IPCS catalyzes the conversion of ceramide to IPC which forms the most predominant sphingolipid in Leishmania. IPCS has no mammalian equivalent and also plays an important role in maintaining the infectivity and viability of the parasite. The present study explores the possibility of targeting IPCS; development of suitable inhibitors for the same would serve as a treatment strategy for the infectious disease leishmaniasis. Five coumarin derivatives were developed as inhibitors of IPCS protein. Molecular dynamics simulations of the complexes of IPCS with these inhibitors were performed which provided insights into the binding modes of the inhibitors. In vitro screening of the top three compounds has resulted in the identification of one of the compounds (compound 3) which shows little cytotoxic effects. This compound therefore represents a good starting point for further in vivo experimentation and could possibly serve as an important drug candidate for the treatment of leishmaniasis.

Mammalian African trypanosome VSG coat enhances tsetse's vector competence

Tsetse flies are biological vectors of African trypanosomes, the protozoan parasites responsible for causing human and animal trypanosomiases across sub-Saharan Africa. Currently, no vaccines are available for disease prevention due to antigenic variation of the Variant Surface Glycoproteins (VSG) that coat parasites while they reside within mammalian hosts. As a result, interference with parasite development in the tsetse vector is being explored to reduce disease transmission. A major bottleneck to infection occurs as parasites attempt to colonize tsetse's midgut. One critical factor influencing this bottleneck is the fly's peritrophic matrix (PM), a semipermeable, chitinous barrier that lines the midgut. The mechanisms that enable trypanosomes to cross this barrier are currently unknown. Here, we determined that as parasites enter the tsetse's gut, VSG molecules released from trypanosomes are internalized by cells of the cardia-the tissue responsible for producing the PM. VSG internalization results in decreased expression of a tsetse microRNA (mir-275) and interferes with the Wnt-signaling pathway and the Iroquois/IRX transcription factor family. This interference reduces the function of the PM barrier and promotes parasite colonization of the gut early in the infection process. Manipulation of the insect midgut homeostasis by the mammalian parasite coat proteins is a novel function and indicates that VSG serves a dual role in trypanosome biology-that of facilitating transmission through its mammalian host and insect vector. We detail critical steps in the course of trypanosome infection establishment that can serve as novel targets to reduce the tsetse's vector competence and disease transmission.

The Glycerol-3-Phosphate Acyltransferase TbGAT is Dispensable for Viability and the Synthesis of Glycerolipids in Trypanosoma brucei

Glycerolipids are the main constituents of biological membranes in Trypanosoma brucei, which causes sleeping sickness in humans. Importantly, they occur as a structural component of the glycosylphosphatidylinositol lipid anchor of the abundant cell surface glycoproteins procyclin in procyclic forms and variant surface glycoprotein in bloodstream form, that play crucial roles for the development of the parasite in the insect vector and the mammalian host, respectively. The present work reports the characterization of the glycerol-3-phosphate acyltransferase TbGAT that initiates the biosynthesis of ester glycerolipids. TbGAT restored glycerol-3-phosphate acyltransferase activity when expressed in a Leishmania major deletion strain lacking this activity and exhibited preference for medium length, unsaturated fatty acyl-CoAs. TbGAT localized to the endoplasmic reticulum membrane with its N-terminal domain facing the cytosol. Despite that a TbGAT null mutant in T. brucei procyclic forms lacked glycerol-3-phosphate acyltransferase activity, it remained viable and exhibited similar growth rate as the wild type. TbGAT was dispensable for the biosynthesis of phosphatidylcholine, phosphatidylinositol, phosphatidylserine, and GPI-anchored protein procyclin. However, the null mutant exhibited a slight decrease in phosphatidylethanolamine biosynthesis that was compensated with a modest increase in production of ether phosphatidylcholine. Our data suggest that an alternative initial acyltransferase takes over TbGAT's function in its absence.

Flagellar membranes are rich in raft-forming phospholipids

The observation that the membranes of flagella are enriched in sterols and sphingolipids has led to the hypothesis that flagella might be enriched in raft-forming lipids. However, a detailed lipidomic analysis of flagellar membranes is not available. Novel protocols to detach and isolate intact flagella from Trypanosoma brucei procyclic forms in combination with reverse-phase liquid chromatography high-resolution tandem mass spectrometry allowed us to determine the phospholipid composition of flagellar membranes relative to whole cells. Our analyses revealed that phosphatidylethanolamine, phosphatidylserine, ceramide and the sphingolipids inositol phosphorylceramide and sphingomyelin are enriched in flagella relative to whole cells. In contrast, phosphatidylcholine and phosphatidylinositol are strongly depleted in flagella. Within individual glycerophospholipid classes, we observed a preference for ether-type over diacyl-type molecular species in membranes of flagella. Our study provides direct evidence for a preferential presence of raft-forming phospholipids in flagellar membranes of T. brucei.

Identification of a glycosylphosphatidylinositol anchor-modifying β1-3 galactosyltransferase in Trypanosoma brucei

Trypanosoma brucei is the causative agent of human African sleeping sickness and the cattle disease nagana.  Trypanosoma brucei is dependent on glycoproteins for its survival and infectivity throughout its life cycle. Here we report the functional characterization of TbGT3, a glycosyltransferase expressed in the bloodstream and procyclic form of the parasite. Bloodstream and procyclic form TbGT3 conditional null mutants were created and both exhibited normal growth under permissive and nonpermissive conditions. Under nonpermissive conditions, the normal glycosylation of the major glycoprotein of bloodstream form T. brucei, the variant surface glycoprotein and the absence of major alterations in lectin binding to other glycoproteins suggested that the major function of TbGT3 occurs in the procyclic form of the parasite. Consistent with this, the major surface glycoprotein of the procyclic form, procyclin, exhibited a marked reduction in molecular weight due to changes in glycosylphosphatidylinositol (GPI) anchor side chains. Structural analysis of the mutant procyclin GPI anchors indicated that TbGT3 encodes a UDP-Gal: β-GlcNAc-GPI β1-3 Gal transferase. Despite the alterations in GPI anchor side chains, TbGT3 conditional null mutants remained infectious to tsetse flies under nonpermissive conditions.

Effects of ingested vertebrate-derived factors on insect immune responses

During the process of blood feeding insect vectors are exposed to an array of vertebrate-derived blood factors ranging from byproducts of blood meal digestion to naturally occurring products in the blood including growth hormones, cytokines and factors derived from blood-borne pathogens themselves. In this review, we examine the ability of these ingested vertebrate blood factors to alter the innate pathogen defenses of insect vectors. The ability of these factors to modify the immune responses of insect vectors offers new intriguing targets for blocking or reducing transmission of human disease-causing pathogens.

High-confidence glycosome proteome for procyclic form Trypanosoma brucei by epitope-tag organelle enrichment and SILAC proteomics

The glycosome of the pathogenic African trypanosome Trypanosoma brucei is a specialized peroxisome that contains most of the enzymes of glycolysis and several other metabolic and catabolic pathways. The contents and transporters of this membrane-bounded organelle are of considerable interest as potential drug targets. Here we use epitope tagging, magnetic bead enrichment, and SILAC quantitative proteomics to determine a high-confidence glycosome proteome for the procyclic life cycle stage of the parasite using isotope ratios to discriminate glycosomal from mitochondrial and other contaminating proteins. The data confirm the presence of several previously demonstrated and suggested pathways in the organelle and identify previously unanticipated activities, such as protein phosphatases. The implications of the findings are discussed.

TbGT8 is a bifunctional glycosyltransferase that elaborates N-linked glycans on a protein phosphatase AcP115 and a GPI-anchor modifying glycan in Trypanosoma brucei

The procyclic form of Trypanosoma brucei expresses procyclin surface glycoproteins with unusual glycosylphosphatidylinositol-anchor side chain structures that contain branched N-acetyllactosamine and lacto-N-biose units. The glycosyltransferase TbGT8 is involved in the synthesis of the branched side chain through its UDP-GlcNAc: βGal β1-3N-acetylglucosaminyltransferase activity. Here, we explored the role of TbGT8 in the mammalian bloodstream form of the parasite with a tetracycline-inducible conditional null T. brucei mutant for TbGT8. Under non-permissive conditions, the mutant showed significantly reduced binding to tomato lectin, which recognizes poly-N-acetyllactosamine-containing glycans. Lectin pull-down assays revealed differences between the wild type and TbGT8 null-mutant T. brucei, notably the absence of a broad protein band with an approximate molecular weight of 110 kDa in the mutant lysate. Proteomic analysis revealed that the band contained several glycoproteins, including the acidic ecto-protein phosphatase AcP115, a stage-specific glycoprotein in the bloodstream form of T. brucei. Western blotting with an anti-AcP115 antibody revealed that AcP115 was approximately 10kDa smaller in the mutant. Enzymatic de-N-glycosylation demonstrated that the underlying protein cores were the same, suggesting that the 10-kDa difference was due to differences in N-linked glycans. Immunofluorescence microscopy revealed the colocalization of hemagglutinin epitope-tagged TbGT8 and the Golgi-associated protein GRASP. These data suggest that TbGT8 is involved in the construction of complex poly-N-acetyllactosamine-containing type N-linked and GPI-linked glycans in the Golgi of the bloodstream and procyclic parasite forms, respectively.

Identification and functional analysis of Trypanosoma cruzi genes that encode proteins of the glycosylphosphatidylinositol biosynthetic pathway

Background

Trypanosoma cruzi is a protist parasite that causes Chagas disease. Several proteins that are essential for parasite virulence and involved in host immune responses are anchored to the membrane through glycosylphosphatidylinositol (GPI) molecules. In addition, T. cruzi GPI anchors have immunostimulatory activities, including the ability to stimulate the synthesis of cytokines by innate immune cells. Therefore, T. cruzi genes related to GPI anchor biosynthesis constitute potential new targets for the development of better therapies against Chagas disease.

Methodology/Principal Findings

In silico analysis of the T. cruzi genome resulted in the identification of 18 genes encoding proteins of the GPI biosynthetic pathway as well as the inositolphosphorylceramide (IPC) synthase gene. Expression of GFP fusions of some of these proteins in T. cruzi epimastigotes showed that they localize in the endoplasmic reticulum (ER). Expression analyses of two genes indicated that they are constitutively expressed in all stages of the parasite life cycle. T. cruzi genes TcDPM1, TcGPI10 and TcGPI12 complement conditional yeast mutants in GPI biosynthesis. Attempts to generate T. cruzi knockouts for three genes were unsuccessful, suggesting that GPI may be an essential component of the parasite. Regarding TcGPI8, which encodes the catalytic subunit of the transamidase complex, although we were able to generate single allele knockout mutants, attempts to disrupt both alleles failed, resulting instead in parasites that have undergone genomic recombination and maintained at least one active copy of the gene.

Conclusions/Significance

Analyses of T. cruzi sequences encoding components of the GPI biosynthetic pathway indicated that they are essential genes involved in key aspects of host-parasite interactions. Complementation assays of yeast mutants with these T. cruzi genes resulted in yeast cell lines that can now be employed in high throughput screenings of drugs against this parasite.

Chagas disease, considered one of the most neglected tropical diseases, is caused by the blood-borne parasite Trypanosoma cruzi and currently affects about 8 million people in Latin America. T. cruzi can be transmitted by insect vectors, blood transfusion, organ transplantation and mother-to-baby as well as through ingestion of contaminated food. Although T. cruzi causes life-long infections that can result in serious damage to the heart, the two drugs currently available to treat Chagas disease, benznidazole and nifurtimox, which have been used for more than 40 years, have proven efficacy only during the acute phase of the disease. Thus, there is an urgent need to develop new drugs that are more targeted, less toxic, and more effective against this parasite. Here we described the characterization of T. cruzi genes involved in the biosynthesis of GPI anchors, a molecule responsible for holding different types of glycoproteins on the parasite membrane. Since GPI anchored proteins are essential molecules T. cruzi uses during infection, besides helping understand how this parasite interacts with its host, this work may contribute to the development of better therapies against Chagas disease.

The effects of ingested mammalian blood factors on vector arthropod immunity and physiology

The blood feeding behavior of disease-transmitting arthropods creates a unique intersection between vertebrate and invertebrate physiology. Here, we review host blood-derived factors that persist through blood digestion to affect the lifespan, reproduction, and immune responses of some of the most common arthropod vectors of human disease.

Creation and characterization of glycosyltransferase mutants of Trypanosoma brucei

The survival strategies of protozoan parasites frequently involve the participation of glycoconjugates. Trypanosoma brucei expresses complex glycoproteins throughout its life cycle and a review of its repertoire of glycosidic linkages suggests a minimum of 38 glycosyltransferase activities. Here we describe a functional characterization workflow in which we create glycosyltransferase null or conditional null mutants in both the bloodstream and procyclic life-cycle forms of the parasite. Subsequently, we characterize the biochemical phenotype of the mutant strains generated and assign precise functions to the genes involved in glycoconjugate biosynthesis and processing in T. brucei. In this way, a comprehensive picture of -T. brucei glycosylation associated genes, their specificities and their relationship to similar genes in other organisms can be obtained.

Options for the delivery of anti-pathogen molecules in arthropod vectors

Blood feeding arthropods are responsible for the transmission of a large array of medically important infectious agents that include viruses, bacteria, protozoan parasites and helminths. The recent development of transgenic and paratransgenic technologies have enabled supplementing the immune system of these arthropod vectors with anti-pathogen effector molecules in view of compromising their vector competence for these microbial agents. The characteristics of the selected anti-pathogen compound will largely determine the efficacy and specificity of this approach. Low specificity will generally result in bystander effects, likely having a direct or indirect fitness cost for the arthropod. In contrast, the use of highly specific compounds from the adaptive immune system of vertebrates such as antibody derived fragments is more likely to enable highly specific effects without conferring a selective disadvantage to the (para)transgenic arthropods. Here, Nanobodies® are excellent candidates to increase the immune competence of arthropods. Moreover they were shown to exert a novel type of anti-pathogen activity that uniquely depends on their small size.

Modeling of the N-glycosylated transferrin receptor suggests how transferrin binding can occur within the surface coat of Trypanosoma brucei

The transferrin receptor of bloodstream form Trypanosoma brucei is a heterodimer encoded by expression site associated genes 6 and 7. This low-abundance glycoprotein with a single glycosylphosphatidylinositol membrane anchor and eight potential N-glycosylation sites is located in the flagellar pocket. The receptor is essential for the parasite, providing its only source of iron by scavenging host transferrin from the bloodstream. Here, we demonstrate that both receptor subunits contain endoglycosidase H-sensitive and endoglycosidase H-resistant N-glycans. Lectin blotting of the purified receptor and structural analysis of the released N-glycans revealed oligomannose and paucimannose structures but, contrary to previous suggestions, no poly-N-acetyllactosamine structures were found. Overlay experiments suggest that the receptor can bind to other trypanosome glycoproteins, which may explain this discrepancy. Nevertheless, these data suggest that a current model, in which poly-N-acetyllactosamine glycans are directly involved in receptor-mediated endocytosis in bloodstream form Trypanosoma brucei, should be revised. Sequential endoglycosidase H and peptide-N-glycosidase F treatment, followed by tryptic peptide analysis, allowed the mapping of oligomannose and paucimannose structures to four of the receptor N-glycosylation sites. These results are discussed with respect to the current model for protein N-glycosylation in the parasite. Finally, the glycosylation data allowed the creation of a molecular model for the parasite transferrin receptor. This model, when placed in the context of a model for the dense variant surface glycoprotein coat in which it is embedded, suggests that receptor N-glycosylation may play an important role in providing sufficient space for the approach and binding of transferrin to the receptor, without significantly disrupting the continuity of the protective variant surface glycoprotein coat.

The tsetse fly transmitted parasite that causes human African trypanosomiasis, or sleeping sickness, scavenges iron from the bloodstream of the infected individual so that it can live, multiply and ultimately cause disease. To do this, it places a glycoprotein (a protein with carbohydrate chains attached) called the transferrin receptor on its surface to capture circulating human transferrin, an iron transport protein. It then internalizes transferrin receptor/transferrin complex and digests the transferrin part, releasing the iron for its own use. By analyzing the parasite transferrin receptor, we have been able to describe the carbohydrate chains of the transferrin receptor and thus complete a molecular model of this important glycoprotein. We have further built models of how we expect this low abundance glycoprotein will sit in the surface coat of the parasite, which is made of millions of copies of another glycoprotein. The results provide a ‘molecule's eye view’ of how the carbohydrate chains of the transferrin receptor provide the space necessary for the transferrin to bind to it without disrupting the protective coat.

KREX2 is not essential for either procyclic or bloodstream form Trypanosoma brucei

BACKGROUND

Most mitochondrial mRNAs in Trypanosoma brucei require RNA editing for maturation and translation. The edited RNAs primarily encode proteins of the oxidative phosphorylation system. These parasites undergo extensive changes in energy metabolism between the insect and bloodstream stages which are mirrored by alterations in RNA editing. Two U-specific exonucleases, KREX1 and KREX2, are both present in protein complexes (editosomes) that catalyze RNA editing but the relative roles of each protein are not known.

METHODOLOGY/PRINCIPAL FINDINGS

The requirement for KREX2 for RNA editing in vivo was assessed in both procyclic (insect) and bloodstream form parasites by methods that use homologous recombination for gene elimination. These studies resulted in null mutant cells in which both alleles were eliminated. The viability of these cells demonstrates that KREX2 is not essential in either life cycle stage, despite certain defects in RNA editing in vivo. Furthermore, editosomes isolated from KREX2 null cells require KREX1 for in vitro U-specific exonuclease activity.

CONCLUSIONS

KREX2 is a U-specific exonuclease that is dispensable for RNA editing in vivo in T. brucei BFs and PFs. This result suggests that the U deletion activity, which is required for RNA editing, is primarily mediated in vivo by KREX1 which is normally found associated with only one type of editosome. The retention of the KREX2 gene implies a non-essential role or a role that is essential in other life cycle stages or conditions.

myo-Inositol uptake is essential for bulk inositol phospholipid but not glycosylphosphatidylinositol synthesis in Trypanosoma brucei

myo-Inositol is an essential precursor for the production of inositol phosphates and inositol phospholipids in all eukaryotes. Intracellular myo-inositol is generated by de novo synthesis from glucose 6-phosphate or is provided from the environment via myo-inositol symporters. We show that in Trypanosoma brucei, the causative pathogen of human African sleeping sickness and nagana in domestic animals, myo-inositol is taken up via a specific proton-coupled electrogenic symport and that this transport is essential for parasite survival in culture. Down-regulation of the myo-inositol transporter using RNA interference inhibited uptake of myo-inositol and blocked the synthesis of the myo-inositol-containing phospholipids, phosphatidylinositol and inositol phosphorylceramide; in contrast, it had no effect on glycosylphosphatidylinositol production. This together with the unexpected localization of the myo-inositol transporter in both the plasma membrane and the Golgi demonstrate that metabolism of endogenous and exogenous myo-inositol in T. brucei is strictly segregated.

The Sphingolipid Biosynthetic Pathway Is a Potential Target for Chemotherapy against Chagas Disease

The protozoan parasite Trypanosoma cruzi is the causative agent of human Chagas disease, for which there currently is no cure. The life cycle of T. cruzi is complex, including an extracellular phase in the triatomine insect vector and an obligatory intracellular stage inside the vertebrate host. These phases depend on a variety of surface glycosylphosphatidylinositol-(GPI-) anchored glycoconjugates that are synthesized by the parasite. Therefore, the surface expression of GPI-anchored components and the biosynthetic pathways of GPI anchors are attractive targets for new therapies for Chagas disease. We identified new drug targets for chemotherapy by taking the available genome sequence information and searching for differences in the sphingolipid biosynthetic pathways (SBPs) of mammals and T. cruzi. In this paper, we discuss the major steps of the SBP in mammals, yeast and T. cruzi, focusing on the IPC synthase and ceramide remodeling of T. cruzi as potential therapeutic targets for Chagas disease.

Transcriptomics and proteomics in human African trypanosomiasis: current status and perspectives

Human African trypanosomiasis, or sleeping sickness, is a neglected vector-borne parasitic disease caused by protozoa of the species Trypanosoma brucei sensu lato. Within this complex species, T. b. gambiense is responsible for the chronic form of sleeping sickness in Western and Central Africa, whereas T. b. rhodesiense causes the acute form of the disease in East Africa. Presently, 1.5 million disability-adjusted life years (DALYs) per year are lost due to sleeping sickness. In addition, on the basis of the mortality, the disease is ranked ninth out of 25 human infectious and parasitic diseases in Africa. Diagnosis is complex and needs the intervention of a specialized skilled staff; treatment is difficult and expensive and has potentially life-threatening side effects. The use of transcriptomic and proteomic technologies, currently in rapid development and increasing in sensitivity and discriminating power, is already generating a large panel of promising results. The objective of these technologies is to significantly increase our knowledge of the molecular mechanisms governing the parasite establishment in its vector, the development cycle of the parasite during the parasite's intra-vector life, its interactions with the fly and the other microbial inhabitants of the gut, and finally human host-trypanosome interactions. Such fundamental investigations are expected to provide opportunities to identify key molecular events that would constitute accurate targets for further development of tools dedicated to field work for early, sensitive, and stage-discriminant diagnosis, epidemiology, new chemotherapy, and potentially vaccine development, all of which will contribute to fighting the disease. The present review highlights the contributions of the transcriptomic and proteomic analyses developed thus far in order to identify potential targets (genes or proteins) and biological pathways that may constitute a critical step in the identification of new targets for the development of new tools for diagnostic and therapeutic purposes.

Inositolphosphoceramide metabolism in Trypanosoma cruzi as compared with other trypanosomatids

Chagas disease is caused by Trypanosoma cruzi and is endemic to North, Central and South American countries. Current therapy against this disease is only partially effective and produces adverse side effects. Studies on the metabolic pathways of T. cruzi, in particular those with no equivalent in mammalian cells, might identify targets for the development of new drugs. Ceramide is metabolized to inositolphosphoceramide (IPC) in T. cruzi and other kinetoplastid protists whereas in mammals it is mainly incorporated into sphingomyelin. In T. cruzi, in contrast to Trypanosoma brucei and Leishmania spp., IPC functions as lipid anchor constituent of glycoproteins and free glycosylinositolphospholipids (GIPLs). Inhibition of IPC and GIPLs biosynthesis impairs differentiation of trypomastigotes into the intracellular amastigote forms. The gene encoding IPC synthase in T. cruzi has been identified and the enzyme has been expressed in a cell-free system. The enzyme involved in IPC degradation and the remodelases responsible for the incorporation of ceramide into free GIPLs or into the glycosylphosphatidylinositols anchoring glycoproteins, and in fatty acid modifications of these molecules of T. cruzi have been understudied. Inositolphosphoceramide metabolism and remodeling could be exploited as targets for Chagas disease chemotherapy.

Lipidomic analysis of bloodstream and procyclic form Trypanosoma brucei

The biological membranes of Trypanosoma brucei contain a complex array of phospholipids that are synthesized de novo from precursors obtained either directly from the host, or as catabolised endocytosed lipids. This paper describes the use of nanoflow electrospray tandem mass spectrometry and high resolution mass spectrometry in both positive and negative ion modes, allowing the identification of approximately 500 individual molecular phospholipids species from total lipid extracts of cultured bloodstream and procyclic form T. brucei. Various molecular species of all of the major subclasses of glycerophospholipids were identified including phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol as well as phosphatidic acid, phosphatidylglycerol and cardolipin, and the sphingolipids sphingomyelin, inositol phosphoceramide and ethanolamine phosphoceramide. The lipidomic data obtained in this study will aid future biochemical phenotyping of either genetically or chemically manipulated commonly used bloodstream and procyclic strains of Trypanosoma brucei. Hopefully this will allow a greater understanding of the bizarre world of lipids in this important human pathogen.

Profiling of lipids in Leishmania donovani using hydrophilic interaction chromatography in combination with Fourier transform mass spectrometry

There is evidence from our current research on resistance to stibigluconate and from some previous observations that lipid composition may be altered in resistant Leishmania donovani and in order to explore this we required a comprehensive lipidomics method. Phospholipids can be analysed by direct infusion into a mass spectrometer and such methods can work very well. However, chromatographic methods can also be very effective and are extensively used. They potentially avoid ion suppression effects, associate lipid classes with a retention time range and deliver good quantitative accuracy. In the current study three chromatography columns were compared for their ability to separate different classes of lipid. Butylsilane (C-4), Zic-HILIC and a silica gel column were compared. The best results were obtained with a silica gel column used in hydrophilic interaction chromatography (HILIC) mode with a mobile phase gradient consisting of (A) 20% isopropyl alcohol (IPA) in acetonitrile (v/v) and (B) 20% IPA in 0.02 M ammonium formate. Using these conditions separate peaks were obtained for triglycerides (TG), phosphoinositols (PI), inositol phosphoceramides (IPC), phosphatidylethanolamines (PE), phosphatidylserines (PS), phosphatidylcholines (PC), sphingosines (SG), lysophosphatidyethanolamines (LPE) and lysophosphatidylcholines (LPC). The methodology was applied to the analysis of lipid extracts from Leishmania donovani and by coupling the chromatography with an LTQ Orbitrap mass spectrometer. It was possible to detect 188 lipid species in the extracts with the following breakdown: PC 59, PE 38, TG 35, PI 20, CPI 13, LPC 11, LPE 2 and SG 10. The fatty acid composition of the more abundant lipids was characterised by MS(2) and MS(3) experiments carried out by using an LCQ Deca low-resolution ion trap instrument coupled with the silica gel column. The separation of lipids into well-defined groups gives extra confidence in their identification and minimises the risk of ion suppression effects. High-resolution mass spectrometry was necessary in order to be able to differentiate between acyl- and acyl-alkyl-lipids.

The essential neutral sphingomyelinase is involved in the trafficking of the variant surface glycoprotein in the bloodstream form of Trypanosoma brucei

Sphingomyelin is the main sphingolipid in Trypanosoma brucei, the causative agent of African sleeping sickness. In vitro and in vivo characterization of the T. brucei neutral sphingomyelinase demonstrates that it is directly involved in sphingomyelin catabolism. Gene knockout studies in the bloodstream form of the parasite indicate that the neutral sphingomyelinase is essential for growth and survival, thus highlighting that the de novo biosynthesis of ceramide is unable to compensate for the loss of sphingomyelin catabolism. The phenotype of the conditional knockout has given new insights into the highly active endocytic and exocytic pathways in the bloodstream form of T. brucei. Hence, the formation of ceramide in the endoplasmic reticulum affects post-Golgi sorting and rate of deposition of newly synthesized GPI-anchored variant surface glycoprotein on the cell surface. This directly influences the corresponding rate of endocytosis, via the recycling endosomes, of pre-existing cell surface variant surface glycoprotein. The trypanosomes use this coupled endocytic and exocytic mechanism to maintain the cell density of its crucial variant surface glycoprotein protective coat. TbnSMase is therefore genetically validated as a drug target against African trypanosomes, and suggests that interfering with the endocytic transport of variant surface glycoprotein is a highly desirable strategy for drug development against African trypanosomasis.

Tsetse flies, trypanosomes, humans and animals: what is proteomics revealing about their crosstalks?

Human and animal African trypanosomoses, or sleeping sickness and Nagana, are neglected vector-borne parasitic diseases caused by protozoa belonging to the Trypanosoma genus. Advances in proteomics offer new tools to better understand host-vector-parasite crosstalks occurring during the complex parasitic developmental cycle, and to determine the outcome of both transmission and infection. In this review, we summarize proteomics studies performed on African trypanosomes and on the interactions with their vector and mammalian hosts. We discuss the contributions and pitfalls of using diverse proteomics tools, and argue about the interest of pathogenoproteomics, both to generate advances in basic research on the best knowledge and understanding of host-vector-pathogen interactions, and to lead to the concrete development of new tools to improve diagnosis and treatment management of trypanosomoses in the near future.

PSSA-2, a membrane-spanning phosphoprotein of Trypanosoma brucei, is required for efficient maturation of infection

The coat of Trypanosoma brucei consists mainly of glycosylphosphatidylinositol-anchored proteins that are present in several million copies and are characteristic of defined stages of the life cycle. While these major components of the coats of bloodstream forms and procyclic (insect midgut) forms are well characterised, very little is known about less abundant stage-regulated surface proteins and their roles in infection and transmission. By creating epitope-tagged versions of procyclic-specific surface antigen 2 (PSSA-2) we demonstrated that it is a membrane-spanning protein that is expressed by several different life cycle stages in tsetse flies, but not by parasites in the mammalian bloodstream. In common with other membrane-spanning proteins in T. brucei, PSSA-2 requires its cytoplasmic domain in order to exit the endoplasmic reticulum. Correct localisation of PSSA-2 requires phosphorylation of a cytoplasmic threonine residue (T₃₀₅), a modification that depends on the presence of TbMAPK4. Mutation of T₃₀₅ to alanine (T₃₀₅A) has no effect on the localisation of the protein in cells that express wild type PSSA-2. In contrast, this protein is largely intracellular when expressed in a null mutant background. A variant with a T₃₀₅D mutation gives strong surface expression in both the wild type and null mutant, but slows growth of the cells, suggesting that it may function as a dominant negative mutant. The PSSA-2 null mutant exhibits no perceptible phenotype in culture and is fully competent at establishing midgut infections in tsetse, but is defective in colonising the salivary glands and the production of infectious metacyclic forms. Given the protein's structure and the effects of mutation of T₃₀₅ on proliferation and localisation, we postulate that PSSA-2 might sense and transmit signals that contribute to the parasite's decision to divide, differentiate or migrate.

Fate of glycosylphosphatidylinositol (GPI)-less procyclin and characterization of sialylated non-GPI-anchored surface coat molecules of procyclic-form Trypanosoma brucei

A Trypanosoma brucei TbGPI12 null mutant that is unable to express cell surface procyclins and free glycosylphosphatidylinositols (GPI) revealed that these are not the only surface coat molecules of the procyclic life cycle stage. Here, we show that non-GPI-anchored procyclins are N-glycosylated, accumulate in the lysosome, and appear as proteolytic fragments in the medium. We also show, using lectin agglutination and galactose oxidase-NaB(3)H(4) labeling, that the cell surface of the TbGPI12 null parasites contains glycoconjugates that terminate in sialic acid linked to galactose. Following desialylation, a high-apparent-molecular-weight glycoconjugate fraction was purified by ricin affinity chromatography and gel filtration and shown to contain mannose, galactose, N-acetylglucosamine, and fucose. The latter has not been previously reported in T. brucei glycoproteins. A proteomic analysis of this fraction revealed a mixture of polytopic transmembrane proteins, including P-type ATPase and vacuolar proton-translocating pyrophosphatase. Immunolocalization studies showed that both could be labeled on the surfaces of wild-type and TbGPI12 null cells. Neither galactose oxidase-NaB(3)H(4) labeling of the non-GPI-anchored surface glycoconjugates nor immunogold labeling of the P-type ATPase was affected by the presence of procyclins in the wild-type cells, suggesting that the procyclins do not, by themselves, form a macromolecular barrier.

The Trypanosoma brucei sphingolipid synthase, an essential enzyme and drug target

Sphingolipids are important components of eukaryotic membranes, particularly the plasma membrane, and are involved in a diverse array of signal transduction processes. In the Eukaryota the biosynthetic pathway for the formation of these lipid species is largely conserved. However, in contrast to mammals which produce sphingomyelin (SM), several pathogenic fungi and protozoa synthesize inositol phosphorylceramide (IPC) as the primary phosphosphingolipid. This process is catalyzed by the enzyme IPC synthase, a recognized target for anti-fungals encoded by the AUR1 gene in yeast. Recently, functional orthologues of the AUR1p have been identified in a group of insect vector-borne pathogenic protozoa, the Kinetoplastida, which are responsible for a range of so-called neglected diseases. Of these the Trypanosoma brucei species are the causative agents of human African trypanosomiasis in many of the most under-developed regions of Africa. The available treatments for these diseases are limited, of decreasing efficacy, and often demonstrate severe side-effects. Against this background the T. brucei sphingolipid synthase, an orthologue of the yeast AUR1p, may represent a promising target for novel anti-protozoals. Our studies identify an isoform of this protein as a novel bi-functional enzyme capable of catalyzing the synthesis of both IPC and SM, both known to be present in the parasite. Furthermore, the synthase is essential for parasite growth and can be inhibited by a known anti-fungal at low nanomolar levels in vitro. Most notably this drug demonstrates trypanocidal activity against cultured bloodstream form parasites. Thus, the T. brucei sphingolipid synthase represents a valid and promising drug target.

Differential trypanosome surface coat regulation by a CCCH protein that co-associates with procyclin mRNA cis-elements

The genome of Trypanosoma brucei is unusual in being regulated almost entirely at the post-transcriptional level. In terms of regulation, the best-studied genes are procyclins, which encode a family of major surface GPI-anchored glycoproteins (EP1, EP2, EP3, GPEET) that show differential expression in the parasite's tsetse-fly vector. Although procyclin mRNA cis-regulatory sequences have provided the paradigm for post-transcriptional control in kinetoplastid parasites, trans-acting regulators of procyclin mRNAs are unidentified, despite intensive effort over 15 years. Here we identify the developmental regulator, TbZFP3, a CCCH-class predicted RNA binding protein, as an isoform-specific regulator of Procyclin surface coat expression in trypanosomes. We demonstrate (i) that endogenous TbZFP3 shows sequence-specific co-precipitation of EP1 and GPEET, but not EP2 and EP3, procyclin mRNA isoforms, (ii) that ectopic overexpression of TbZFP3 does not perturb the mRNA abundance of procyclin transcripts, but rather that (iii) their protein expression is regulated in an isoform-specific manner, as evidenced by mass spectrometric analysis of the Procyclin expression signature in the transgenic cell lines. The TbZFP3 mRNA–protein complex (TbZFP3mRNP) is identified as a trans-regulator of differential surface protein expression in trypanosomes. Moreover, its sequence-specific interactions with procyclin mRNAs are compatible with long-established predictions for Procyclin regulation. Combined with the known association of TbZFP3 with the translational apparatus, this study provides a long-sought missing link between surface protein cis-regulatory signals and the gene expression machinery in trypanosomes.

Trypanosomes, the tropical parasites that cause African sleeping sickness, show a number of biological peculiarities that distinguish them from other eukaryotes. One is the unusual way in which they regulate gene expression. Unlike most eukaryotes, trypanosomes do not regulate gene expression by controlling the rate of messenger RNA synthesis, but, instead, control the stability of messenger mRNAs (and, hence, their abundance) and also their rate of translation into protein. The best-studied model for this “post-transcriptional” gene expression control in trypanosomes is the procyclin mRNAs, which encode the major surface proteins of the parasite in the tsetse fly. In this study we demonstrate that a small kinetoplastid-specific protein (TbZFP3) co-associates with the mRNAs for some procyclin isoforms (EP1, GPEET procyclin) but not others (EP2, EP3 procyclin). Furthermore, we show that this is dependent upon sequences in the EP1 procyclin 3′untranslated region known to govern its mRNA turnover and protein synthesis. Finally, we demonstrate that limited over-expression of TbZFP3 causes a change in the surface protein expression profile on cultured parasites from GPEET to EP1 Procyclin. Our data identify TbZFP3 as an important post-transcriptional regulator of Procyclin expression, the first such protein factor identified.