Silencing of tachyzoite enolase 2 alters nuclear targeting of bradyzoite enolase 1 in Toxoplasma gondii

Toxoplasma gondii DNA methyltransferases regulate parasitic energy metabolism

The intracellular protozoan Toxoplasma gondii results in serious diseases such as encephalitis, and retinochoroiditis in immunocompromised patients. The interconversion between tachyzoites and bradyzoites under the host's immune pressure results in the interchange of acute infection and chronic infection. We previously reported two functional DNA methyltransferases (DNMT) in Toxoplasma gondii named TgDNMTa and TgDNMTb. In this research, proteomics analysis for T. gondii tachyzoites of ME49 WT, dnmta knockout (ME49-∆Tgdnmta), and dnmtb knockout (ME49-∆Tgdnmtb) strains, revealed 362 significantly regulated proteins for ME49-∆Tgdnmta, and 219 for ME49-∆Tgdnmtb, compared with the proteins of ME49 WT. TgDNMTa down regulated three glycolytic enzymes, one gluconeogenic enzyme and four pyruvate metabolic enzymes. Furthermore, TgDNMTb up regulated two proteins in the tricarboxylic acid (TCA) cycle. Glucose metabolic flux detection showed that TgDNMTa inhibited the glycolysis pathway, while TgDNMTb promoted the tricarboxylic acid (TCA) cycle so as to promote parasite's proliferation. These findings demonstrated that the functions of Toxoplasma gondii DNA methyltransferases extended beyond DNA methylation to the regulation of parasitic energy metabolism.

Identification and functional characterization of the siRNA pathway in Taenia crassiceps by silencing Enolase A

A gene silencing procedure on cysticerci of the taeniid cestode Taenia crassiceps is described. This is the first time this technique is reported in this species that is widely used as an animal model for human cysticercosis. Genome database searches were performed in order to find out if relevant genes involved in gene silencing and non-coding RNA processing, Argonaute and Dicer (AGO and Dcr) are present in T. crassiceps. We found three AGO and two Dcr orthologues that were designed TcAGO1, Tc2 and Tc3, as well as TcDcr1 and TcDcr2. In order to elucidate the evolutionary relationships of T. crassiceps TcAGO and TcDcr genes, separate phylogenetic analyses were carried out for each, including AGO and Dcr orthologues of other 20 platyhelminthes. Our findings showed a close phylogenetic relationship of TcAGO and TcDcr with those previously described for Echinococcus spp. Our RT-PCR studies demonstrated expression of all TcAGO and TcDcr orthologues. Our results show that the gene silencing machinery in T. crassiceps is functionally active by inducing silencing of TcEnoA (∼90%). These results clearly show that gene silencing using siRNAs can be used as a molecular methodology to study gene function in taeniid cestodes.

Molecular and biochemical characterization of Taenia solium α-enolase

Enolase (EC 4.2.1.11) acts as a multifunctional enzyme in many organisms, being involved in metabolism, transcription regulation and pathogenesis. In the current study, the recombinant α-enolase from Taenia solium (His-Tseno) was prepared and antiserum against His-Tseno was generated in rabbits. Consequently, we analyzed the enzymatic characteristics, plasminogen binding activity, tissue localization and expression patterns of Tseno. The study demonstrated that the enzymatic activity of His-Tseno was enhanced at pH around 7.0-7.5 and affected by addition of metal ions. Kinetic measurements using 2-phospho-d-glycerate (2-PGA) substrates gave a specific activity of 60.72 ± 0.84 U/mg and 1.1 mM of Km_2-PGA value. Plasminogen binding assay showed that His-Tseno could bind to human plasminogen and generate plasmin activated by a tissue-type plasminogen activator (t-PA). In addition, the lysine analogue 6-aminocaproic acid (ε-ACA) could inhibit the binding of plasminogen to His-Tseno. Quantitative real-time PCR confirmed that Tseno was expressed 2.38 folds higher in the adult worms (p < 0.05) than in the cysticerci. Further, an immunolocalization assay indicated that native Tseno was mainly distributed in the tegument and eggs of gravid proglottis from adult T. solium. In conclusion, Tseno executes the innate glycolytic function to supply energy for the growth, egg production, and even invasion of T. solium.

Immunolocation and enzyme activity analysis of Cryptosporidium parvum enolase

Background

Enolase is an essential multifunctional glycolytic enzyme that is involved in many biological processes of apicomplexan protozoa, such as adhesion and invasion. However, the characteristics of enolase in Cryptosporidium parvum, including the location on the oocyst and the enzyme activity, remain unclear.

Methods

The C. parvum enolase gene (cpeno) was amplified by RT-PCR and sequenced. The deduced amino acid sequence was analysed by bioinformatics software. The gene was expressed in Escherichia coli BL21 (DE3) and purified recombinant protein was used for enzyme activity analysis, binding experiments and antibody preparation. The localisation of enolase on oocysts was examined via immunofluorescence techniques.

Results

A 1,350 bp DNA sequence was amplified from cDNA taken from C. parvum oocysts. The deduced amino acids sequence of C. parvum enolase (CpEno) had 82.1% homology with Cryptosporidium muris enolase, and 54.7–68.0% homology with others selected species. Western blot analysis indicated that recombinant C. parvum enolase (rCpEno) could be recognised by C. parvum-infected cattle sera. Immunolocalization testing showed that CpEno was found to locate mainly on the surface of oocysts. The enzyme activity was 33.5 U/mg, and the Michaelis constant (K_m) was 0.571 mM/l. Kinetic measurements revealed that the most suitable pH value was 7.0–7.5, and there were only minor effects on the activity of rCpEno with a change in the reaction temperature. The enzyme activity decreased when the Ca²⁺, K⁺, Mg²⁺ and Na⁺ concentrations of the reaction solution increased. The binding assays demonstrated that rCpEno could bind to human plasminogen.

Conclusion

This study is the first report of immunolocation, binding activity and enzyme characteristics of CpEno. The results of this study suggest that the surface-associated CpEno not only functions as a glycolytic enzyme but may also participate in attachment and invasion process of the parasite.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2200-y) contains supplementary material, which is available to authorized users.

Identification and characterization of an immunogenic antigen, enolase 2, among excretory/secretory antigens (ESA) of Toxoplasma gondii

An immunogenic protein, enolase 2, was identified among the secreted excretory/secretory antigens (ESAs) from Toxoplasma gondii strain RH using immunoproteomics based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Enolase 2 was cloned, sequenced, and heterologously expressed. BLAST analysis revealed 75-96% similarity with enolases from other parasites. Immunoblotting demonstrated good immunoreactivity of recombinant T. gondii enolase (Tg-enolase 2) to T. gondii-infected animal serum. Purified Tg-enolase 2 was found to catalyze dehydration of 2-phospho-d-glycerate to phosphoenolpyruvate. In vitro studies revealed maximal activity at pH 7.5 and 37 °C, and activity was inhibited by K(+), Ni(2+), Al(3+), Na(+), Cu(2+) and Cr(3+). A monoclonal antibody against Tg-enolase 2 was prepared, 1D6, with the isotype IgG2a/κ. Western blotting revealed that 1D6 reacts with Tg-enolase 2 and native enolase 2, present among T. gondii ESAs. The indirect immunofluorescence assays showed that enolase 2 could be specifically detected on the growing T. gondii tachyzoites. Immunoelectron microscopy revealed the surface and intracellular locations of enolase 2 on T. gondii cells. In conclusion, our results clearly show that the enzymatic activity of T. gondii enolase 2 is ion dependent and that it could be influenced by environmental factors. We also provide evidence that enolase 2 is an important immunogenic protein of ESAs from T. gondii and that it is a surface-exposed protein with strong antigenicity and immunogenicity. Our findings indicate that enolase 2 could play important roles in metabolism, immunogenicity and pathogenicity and that it may serve as a novel drug target and candidate vaccine against T. gondii infection.

Twenty-six circulating antigens and two novel diagnostic candidate molecules identified in the serum of canines with experimental acute toxoplasmosis

BACKGROUND

The protozoan Toxoplasma gondii is a pathogen that causes severe opportunistic disease in a wide range of hosts. Efficient methods to diagnose acute T. gondii infection are essential for the administration of appropriate treatments and to reduce economic losses. In animals with acute infections, circulating antigens (CAgs) were detected as early as two days post-infection; these CAgs were reliable diagnostic indicators of acute infection. However, only a limited number of CAgs have been identified to date. The objective of this study was to identify a broader spectrum of CAgs and to explore novel diagnostic candidates in serum.

METHODS

A canine model of acute toxoplasmiosis was established. For this purpose, six dogs were infected by intraperitoneal inoculation of tachyzoites. The CAgs spectrum in the serum was identified with the immunoprecipitation-shotgun approach. Two CAgs with low homology to other species, coronin protein (TgCOR) and ELMO protein (TgELMO), were heterologously expressed in Escherichia coli. Polyclonal antibodies against these two proteins were prepared, and the presence of these proteins in the serum was verified by Western blotting. The two CAgs were detected and evaluated by indirect ELISA methods.

RESULTS

The CAgs levels peaked between two and five days after inoculation, and twenty-six CAgs were identified. Western blotting showed the presence of the two proteins in the serum during acute infection. Based on ELISA tests, the two CAgs were detected during acute infection.

CONCLUSIONS

We identified twenty-six CAgs in the serum of canines with experimental acute toxoplasmosis and discovered two novel diagnostic candidates. We also provide new insights into the diagnosis of acute toxoplasmosis.

Antisense technologies in the studying of Toxoplasma gondii

This review covers a brief history of antisense RNAs and its applications, and summarizes the current stage of antisense technologies used in Toxoplasma gondii, a fascinating model organism with a unique characteristic blend of genetic regulatory systems normally found in plants or animals. Based on the current knowledge of regulatory RNAs and non-coding RNA (ncRNA), the antisense technologies are reviewed according to the classification of ncRNAs, which are roughly categorized into small, ranging from ~20-200 nucleotides in length, and long >200 nucleotides. Techniques utilizing small regulatory RNAs such as siRNA, miRNA, antagomirs, ribozymes and morpholino oligomers are discussed along with long non-coding RNA (lncRNA) including antisense and double stranded. These antisense technologies can be used in forward and reverse genetics studies. The future of technologies is limitless, particularly by combining these technologies with conventional methods, and should allow for ever greater understanding of gene regulation of the organism and related pathogenic microorganisms.

Identification and functional characterization of alpha-enolase from Taenia pisiformis metacestode

Enolase belongs to glycolytic enzymes with moonlighting functions. The role of enolase in Taenia species is still poorly understood. In this study, the full length of cDNA encoding for Taenia pisiformis alpha-enolase (Tpeno) was cloned from larval parasites and soluble recombinant Tpeno protein (rTpeno) was produced. Western blot indicated that both rTpeno and the native protein in excretion-secretion antigens from the larvae were recognized by anti-rTpeno monoclonal antibodies (MAbs). The primary structure of Tpeno showed the presence of a highly conserved catalytic site for substrate binding and an enolase signature motif. rTpeno enzymatic activities of catalyzing the reversible dehydration of 2-phosphoglycerate (2-PGA) to phosphoenolpyruvate (PEP) and vice versa were shown to be 30.71 ± 2.15 U/mg (2-PGA to PEP) and 11.29 ± 2.38 U/mg (PEP to 2-PGA), respectively. Far-Western blotting showed that rTpeno could bind to plasminogen, however its binding ability was inhibited by ϵ-aminocaproic acid (ϵACA) in a competitive ELISA test. Plasminogen activation assay showed that plasminogen bound to rTpeno could be converted into active plasmin using host-derived activators. Immunohistochemistry and immunofluorescence indicated that Tpeno was distributed in the bladder wall of the metacestode and the periphery of calcareous corpuscles. In addition, a vaccine trial showed that the enzyme could produce a 36.4% protection rate in vaccinated rabbits against experimental challenges from T. pisiformis eggs. These results suggest that Tpeno with multiple functions may play significant roles in the migration, growth, development and adaptation of T. pisiformis for survival in the host environment.

Nuclear glycolytic enzyme enolase of Toxoplasma gondii functions as a transcriptional regulator

Apicomplexan parasites including Toxoplasma gondii have complex life cycles within different hosts and their infectivity relies on their capacity to regulate gene expression. However, little is known about the nuclear factors that regulate gene expression in these pathogens. Here, we report that T. gondii enolase TgENO2 is targeted to the nucleus of actively replicating parasites, where it specifically binds to nuclear chromatin in vivo. Using a ChIP-Seq technique, we provide evidence for TgENO2 enrichment at the 5′ untranslated gene regions containing the putative promoters of 241 nuclear genes. Ectopic expression of HA-tagged TgENO1 or TgENO2 led to changes in transcript levels of numerous gene targets. Targeted disruption of TgENO1 gene results in a decrease in brain cyst burden of chronically infected mice and in changes in transcript levels of several nuclear genes. Complementation of this knockout mutant with ectopic TgENO1-HA fully restored normal transcript levels. Our findings reveal that enolase functions extend beyond glycolytic activity and include a direct role in coordinating gene regulation in T. gondii.

Identification of differentially expressed proteins in sulfadiazine resistant and sensitive strains of Toxoplasma gondii using difference-gel electrophoresis (DIGE)

Treatment options for toxoplasmosis in humans are generally limited to the use of sulfonamide and/or pyrimethamine-based compounds. However, there is increasing evidence for clinical therapy failures in patients suggesting the existence of drug resistance in these classes of drug. In vitro resistance to sulfadiazine has been detected in three strains of Toxoplasma gondii isolated from clinical cases. In order to begin to understand the mechanisms of resistance, we undertook a difference-gel electrophoresis (DIGE) approach combined with mass spectrometry to identify proteins that are differentially expressed in sulfadiazine-resistance strains of the parasite. Naturally resistant strains TgA 103001 (Type I), TgH 32006 (Type II) and TgH 32045 (Type II variant) were compared to sensitive strains RH (Type I) and ME-49 (Type II) using DIGE and the modulated proteins analyzed using LC–MS/MS. In total, 68 differentially expressed protein spots were analyzed by mass spectrometer and 31 unique proteins, including four hypothetical proteins, were identified. Among the differentially expressed proteins, 44% were over-expressed in resistant strains and 56% were over-expressed in sensitive strains. The virulence-associated rhoptry protein, ROP2A, was found in greater abundance in both naturally resistant Type II strains TgH 32006 and TgH 32045 compared to the sensitive strain ME-49. Enolase 2 and IMC1 were found to be in greater abundance in sensitive strains RH and ME-49, and MIC2 was found to be more abundant in the sensitive strain ME-49. Proteins regulation of ROP2, MIC2, ENO2, IMC1 and GRA7 were confirmed by Western blot analysis. In addition, gene expression patterns of ROP2, MIC2, ENO2 and IMC1 were analyzed with qRT-PCR. This study provides the first proteomics insights into sulfadiazine resistance in T. gondii resistant strains isolated from clinical cases.

Gene silencing in parasites: current status and future prospects

Parasitic diseases cause important losses in public and veterinary health worldwide. Novel drugs, more reliable diagnostic techniques and vaccine candidates are urgently needed. Due to the complexity of parasites and the intricate relationship with their hosts, development of successful tools to fight parasites has been very limited to date. The growing information on individual parasite genomes is now allowing the use of a broader range of potential strategies to gain deeper insights into the host-parasite relationship and has increased the possibilities to develop molecular-based tools in the field of parasitology. Nevertheless, functional studies of respective genes are still scarce. The RNA interference phenomenon resulting in the regulation of protein expression through the specific degradation of defined mRNAs, and more specifically the possibility of artificially induce it, has shown to be a powerful tool for the investigation of proteins function in many organisms. Recent advances in the design and delivery of targeting molecules allow efficient and highly specific gene silencing in different types of parasites, pointing out this technology as a powerful tool for the identification of novel vaccine candidates or drug targets at the high-throughput level in the near future, and could enable researchers to functionally annotate parasite genomes. The aim of this review is to provide a comprehensive overview on the current advances and pitfalls in gene silencing mechanisms, techniques, applications and prospects in animal parasites.

RNA interference in protozoan parasites: achievements and challenges

Protozoan parasites that profoundly affect mankind represent an exceptionally diverse group of organisms, including Plasmodium, Toxoplasma, Entamoeba, Giardia, trypanosomes, and Leishmania. Despite the overwhelming impact of these parasites, there remain many aspects to be discovered about mechanisms of pathogenesis and how these organisms survive in the host. Combined with the ever-increasing availability of sequenced genomes, RNA interference (RNAi), discovered a mere 13 years ago, has enormously facilitated the analysis of gene function, especially in organisms that are not amenable to classical genetic approaches. Here we review the current status of RNAi in studies of parasitic protozoa, with special emphasis on its use as a postgenomic tool.

Reverse vaccinology approach identify an Echinococcus granulosus tegumental membrane protein enolase as vaccine candidate

Applying reverse vaccinology strategy, we employed a sequence encoding an enolase from Taenia asiatica to search its homolog in the expression sequence tag (EST) database of Echinococcus granulosus and found two EST sequences (Access number: CN653186 and CN649593) of a clone Eg_PSGRS_13B09 from E. granulosus protoscolex full-length cDNA library, which are responding for the 5' and 3' partial cds of E. granulosus enolase, respectively. Primers are designed according to the 5' end and 3'end of the putative encoding sequence to amplify the genomic DNA of E. granulosus strain isolated from sheep in Qinghai province of China by polymerase chain reaction (PCR). A sole product of 1,449 bp in length was obtained, which contains two little introns of 78 bp and 69 bp, respectively. The introns were excised by unsymmetrical PCR with combined flank sequences of introns as primers. The structural, functional, and immunological characteristics of putative amino acid sequence were predicted by bioinformatics analysis. The complete coding sequence was predicted to encode 433 residues and contain a transmembrane region aa(104-124), with the N terminus outside and C terminus inside. The inside part is quite the functional domain. SWISS-MODEL modulated its 3D structure as a barrel which constitutes of alternatively arranged alpha helix-beta sheet, with the key sites such as substrate binding region, active sites, Mg(2+)-binding sites closely located at the center. The protein contains a potential nuclear localization sequence aa(190-199) and several linear B cell epitopes and CTL T cell epitopes, of which the outside epitope aa(49-57) and inside epitope aa(228-236) are facultative T cell and B cell epitope, and the linear B cell epitope aa(206-213) contains the active center site Glu(210), suggesting the putative protein is a potential membrane with strong immunogenicity. The complete cds was expressed in Escherichia coli, and the recombinant protein can be recognized by the serum from patient infected with E. granulosus. Reverse vaccinology process identified E. granulosus tegumental membrane protein enolase as vaccine candidate.