Identification of novel glutathione transferases in Echinococcus granulosus. An evolutionary perspective

Immunization with a Mu-class glutathione transferase from Echinococcus granulosus induces efficient antibody responses and confers long-term protection against secondary cystic echinococcosis

Cystic echinococcosis, a zoonosis caused by cestodes belonging to the Echinococcus granulosus sensu lato (s.l.) genetic complex, affects humans and diverse livestock species. Although a veterinary vaccine exhibiting high levels of antibody-mediated protection has successfully reached the market, the large genetic diversity among parasite isolates and their particular host preferences, makes still necessary the search for novel vaccine candidates. Glutathione transferases (GSTs) constitute attractive targets for immunoprophylaxis due to their outstanding relevance in helminth detoxification processes, against both exogenous and endogenous stressors. Among the six GSTs known to be expressed in E. granulosus s.l., EgGST1 (Mu-class), EgGST2 (Sigma-class), and EgGST3 (a still non-classifiable isoenzyme), show the highest proteomic expression. Therefore, their recombinant forms -rEgGST1, rEgGST2 and rEgGST3- were herein analyzed regarding their potential to induce long-term antiparasite protection in mice. Only immunization with rEgGST1 induced long-lasting protection; and accordingly, rEgGST1-specific antibodies enhanced the parasite killing through both the classical activation of the host complement system and the antibody-dependent cellular cytotoxicity by macrophages. These results support further testing of rEgGST1 as a vaccine candidate in diverse hosts due to the broad expression of EgGST1 in different parasite stages and tissues.

Biochemical characterization and gene structure analysis of the 24-kDa glutathione transferase sigma from Taenia solium

Taenia solium can cause human taeniasis and/or cysticercosis. The latter can in some instances cause human neurocysticercosis which is considered a priority in disease-control strategies and the prevention of mental health problems. Glutathione transferases are crucial for the establishment and long-term survival of T. solium; therefore, we structurally analyzed the 24-kDa glutathione transferase gene (Ts24gst) of T. solium and biochemically characterized its product. The gene promoter showed potential binding sites for transcription factors and xenobiotic regulatory elements. The gene consists of a transcription start site, four exons split by three introns, and a polyadenylation site. The gene architecture is conserved in cestodes. Recombinant Ts24GST (rTs24GST) was active and dimeric. Anti-rTs24GST serum showed slight cross-reactivity with human sigma-class GST. A 3D model of Ts24GST enabled identification of putative residues involved in interactions of the G-site with GSH and of the H-site with CDNB and prostaglandin D2. Furthermore, rTs24GST showed optimal activity at 45 °C and pH 9, as well as high structural stability in a wide range of temperatures and pHs. These results contribute to the better understanding of this parasite and the efforts directed to fight taeniasis/cysticercosis.

A dominance of Mu class glutathione transferases within the equine tapeworm Anoplocephala perfoliata

The most common equine tapeworm, Anoplocephala perfoliata, has often been neglected amongst molecular investigations and has been faced with limited treatment options. However, the recent release of a transcriptome dataset has now provided opportunities for in-depth analysis of A. perfoliata protein expression. Here, global, and sub-proteomic approaches were utilized to provide a comprehensive characterization of the A. perfoliata soluble glutathione transferases (GST) (ApGST). Utilizing both bioinformatics and gel-based proteomics, GeLC and 2D-SDS PAGE, the A. perfoliata ‘GST-ome’ was observed to be dominated with Mu class GST representatives. In addition, both Sigma and Omega class GSTs were identified, albeit to a lesser extent and absent from affinity chromatography approaches. Moreover, 51 ApGSTs were localized across somatic (47 GSTs), extracellular vesicles (EVs) (Whole: 1 GST, Surface: 2 GSTs) and EV depleted excretory secretory product (ESP) (9 GSTs) proteomes. In related helminths, GSTs have shown promise as novel anthelmintic or vaccine targets for improved helminth control. Thus, provides potential targets for understanding A. perfoliata novel infection mechanisms, host–parasite relationships and anthelmintic treatments.

Identification of Omega-class glutathione transferases in helminths of the Taeniidae family

Glutathione transferase enzymes (GSTs) are believed to be a major detoxification system in helminth parasites and have been associated with immunomodulation of the host response. Echinococcus granulosus sensu lato (s.l.) is a cestode parasite known to express at least five different GSTs, but no Omega-class enzymes have been reported in this parasite or in any other cestode. Herein we report the identification of a new member of the GST superfamily in E. granulosus s.l., which is phylogenetically related to the Omega-class: EgrGSTO. Through mass spectrometry, we showed that the 237 amino acids protein EgrGSTO is expressed by the parasite. Moreover, we identified homologues of EgrGSTO in other eight members of the Taeniidae family, including E. canadensis, E. multilocularis, E. oligarthrus, Hydatigera taeniaeformis, Taenia asiatica, T. multiceps, T. saginata and T. solium. A manual sequence inspection and rational modification yielded eight Taeniidae's GSTO sequences, each one encoding for a 237 aa polypeptide showing 80.2% overall identity. To the best of our knowledge, this is the first description of genes encoding for Omega-class GSTs in worms belonging to the Taeniidae family -that at least in E. granulosus s.l. is expressed as a protein- suggesting the gene encodes for a functional protein.

Molecular characteristics of glutathione transferase gene family in a neglect medical Spirometra tapeworm

The Spirometra mansoni is a neglect medical tapeworm, its plerocercoid larvae can parasitize in humans and animals, causing sparganosis. In this study, 17 new members of the glutathione transferase (GST) family were sequenced and characterized in S. mansoni. Clustering analysis displayed the categorization of SmGSTs into two main clades. RT-qPCR illustrated that 7 GST genes were highly expressed in the plerocercoid stage while 8 GSTs were highly expressed in the adult. rSmGST has the typical C- and N-terminal double domains of glutathione transferase. Immunolocalization revealed that natural SmGST is mainly located in the epidermis and parenchyma of plerocercoid, and in the epidermis, parenchyma, uterus and egg shell of adult worm. The optimum activity for rSmGST was found to be pH 6.5 and 25°C. The evolutionary tree showed a high level of diversity of cestodes GSTs. SmGSTs contained both conserved family members and members in the process of further diversification. The findings in this study will lay a foundation to better explore the underlying mechanisms of GSTs involved in Spirometra tapeworms.

Expanding the family of Mu-class glutathione transferases in the cestode parasite Echinococcus granulosus sensu lato

Glutathione transferases (GSTs) perform catalytic and non-catalytic activities, mostly involved in stress-response and cell detoxification. Helminth parasites express several GSTs of multiple classes that are involved in the neutralization of potentially harmful oxidants, and in the inactivation or removal of xenobiotics. Additionally, GSTs participate in immunomodulatory processes that facilitate the parasite establishment and survival within its host. In Echinococcus granulosus sensu lato (s.l.) -the cestode parasite responsible for cystic echinococcosis- only one Mu-class GST has been reported. In the present work, by using bioinformatic and proteomic approaches we searched for novel Mu-class GSTs potentially involved in the parasite oxidative-stress metabolism. In the genome of E. granulosus s.l., 6 GST-related sequences were found to constitute a strongly conserved phylogenetical clade with Mu-class members. Among them, 5 displayed conserved gene structure (exon/intron), as well as specific residues and motifs characteristic of Mu-class enzymes. By proteomic analysis, 3 Mu-GSTs were identified to be expressed in the protoscolex parasite stage, 2 of them being firstly described as Mu-class GSTs here. The existence of more than one productive Mu-GST gene expands the parasite xenobiotic phase II metabolism, which might have beneficial roles on E. granulosus s.l. ability to successfully infect its host.

Evolutionary Adaptations of Parasitic Flatworms to Different Oxygen Tensions

During the evolution of the Earth, the increase in the atmospheric concentration of oxygen gave rise to the development of organisms with aerobic metabolism, which utilized this molecule as the ultimate electron acceptor, whereas other organisms maintained an anaerobic metabolism. Platyhelminthes exhibit both aerobic and anaerobic metabolism depending on the availability of oxygen in their environment and/or due to differential oxygen tensions during certain stages of their life cycle. As these organisms do not have a circulatory system, gas exchange occurs by the passive diffusion through their body wall. Consequently, the flatworms developed several adaptations related to the oxygen gradient that is established between the aerobic tegument and the cellular parenchyma that is mostly anaerobic. Because of the aerobic metabolism, hydrogen peroxide (H₂O₂) is produced in abundance. Catalase usually scavenges H₂O₂ in mammals; however, this enzyme is absent in parasitic platyhelminths. Thus, the architecture of the antioxidant systems is different, depending primarily on the superoxide dismutase, glutathione peroxidase, and peroxiredoxin enzymes represented mainly in the tegument. Here, we discuss the adaptations that parasitic flatworms have developed to be able to transit from the different metabolic conditions to those they are exposed to during their life cycle.

Expression and distribution of glutathione transferases in protoscoleces of Echinococcus granulosus sensu lato

Glutathione transferases (GSTs) belong to a diverse superfamily of multifunctional proteins involved in metabolic detoxification. In helminth parasite, GSTs are particularly relevant since they are also involved in host immunomodulation. Echinococcus granulosus sensu lato (s.l.) is a cestode parasite known to express at least three phylogenetically distant cytosolic GSTs: EgGST1 and EgGST2 previously grouped within Mu and Sigma classes, respectively; and EgGST3 related to both Omega and Sigma classes. To better characterize E. granulosus s.l. GSTs, herein their expression and distribution were assessed in the pre-adult protoscolex (PSC) parasite stage. Potential transcriptional regulatory mechanisms of the corresponding EgGST genes were also explored. Firstly, the transcription of the three EgGSTs was significantly induced during the early stages of the murine model of infection, suggesting a potential role during parasite establishment. EgGST1 was detected in the parenchyma of PSCs and its expression increased after H₂O₂ exposure, supporting its role in detoxification. EgGST2 was mainly detected on the PSCs tegument, strategically localized for potential immunoregulation functions due to its Sigma-class characteristics. In addition, its expression increased after anthelmintic treatment, suggesting a role in chemotherapy resistance. Finally, the Omega-related EgGST3 was localized throughout the entire PSC body, including suckers and tegument, and since its expression also increased after H₂O₂ treatment, a potential role in oxidative stress response could also be ascribed. On the other hand, known cis-acting regulatory motifs were detected in EgGST genes, suggesting similar transcription processes to other eukaryotes. The results herein reported provide additional data regarding the roles of EgGSTs in E. granulosus s.l. biology, contributing to a better understanding of its host-parasite interaction.

Evidence of Immune Modulators in the Secretome of the Equine Tapeworm Anoplocephala perfoliata

Anoplocephala perfoliata is a neglected gastro-intestinal tapeworm, commonly infecting horses worldwide. Molecular investigation of A. perfoliata is hampered by a lack of tools to better understand the host-parasite interface. This interface is likely influenced by parasite derived immune modulators released in the secretome as free proteins or components of extracellular vesicles (EVs). Therefore, adult RNA was sequenced and de novo assembled to generate the first A. perfoliata transcriptome. In addition, excretory secretory products (ESP) from adult A. perfoliata were collected and EVs isolated using size exclusion chromatography, prior to proteomic analysis of the EVs, the EV surface and EV depleted ESP. Transcriptome analysis revealed 454 sequences homologous to known helminth immune modulators including two novel Sigma class GSTs, five α-HSP90s, and three α-enolases with isoforms of all three observed within the proteomic analysis of the secretome. Furthermore, secretome proteomics identified common helminth proteins across each sample with known EV markers, such as annexins and tetraspanins, observed in EV fractions. Importantly, 49 of the 454 putative immune modulators were identified across the secretome proteomics contained within and on the surface of EVs in addition to those identified in free ESP. This work provides the molecular tools for A. perfoliata to reveal key players in the host-parasite interaction within the horse host.

Unraveling oxidative stress response in the cestode parasite Echinococcus granulosus

Cystic hydatid disease (CHD) is a worldwide neglected zoonotic disease caused by Echinococcus granulosus. The parasite is well adapted to its host by producing protective molecules that modulate host immune response. An unexplored issue associated with the parasite's persistence in its host is how the organism can survive the oxidative stress resulting from parasite endogenous metabolism and host defenses. Here, we used hydrogen peroxide (H₂O₂) to induce oxidative stress in E. granulosus protoescoleces (PSCs) to identify molecular pathways and antioxidant responses during H₂O₂ exposure. Using proteomics, we identified 550 unique proteins; including 474 in H₂O₂-exposed PSCs (H-PSCs) samples and 515 in non-exposed PSCs (C-PSCs) samples. Larger amounts of antioxidant proteins, including GSTs and novel carbonyl detoxifying enzymes, such as aldo-keto reductase and carbonyl reductase, were detected after H₂O₂ exposure. Increased concentrations of caspase-3 and cathepsin-D proteases and components of the 26S proteasome were also detected in H-PSCs. Reduction of lamin-B and other caspase-substrate, such as filamin, in H-PSCs suggested that molecular events related to early apoptosis were also induced. We present data that describe proteins expressed in response to oxidative stress in a metazoan parasite, including novel antioxidant enzymes and targets with potential application to treatment and prevention of CHD.

Characterization of catalytic and non-catalytic activities of EgGST2-3, a heterodimeric glutathione transferase from Echinococcus granulosus

Glutathione transferases (GSTs) perform several catalytic and non-catalytic roles in the defense against toxicities of electrophile compounds and oxidative stress, and therefore are involved in stress-response and cell detoxification. Previously, we have provided evidence indicating that EgGST2 and EgGST3, two phylogenetically distant Echinococcus granulosus GSTs, can naturally form a heterodimeric structure (EgGST2-3). In the present work, the recombinant heterodimer GST (rEgGST2-3) is characterized. Hence, rEgGST2-3 was able to conjugate GSH to three substrates: 1-chloro-2,4-dinitrobenzene (CDNB, general substrate for GSTs), 1,2-dichloro-4-nitrobenzene (specific substrate for mammalian Mu class) and trans,trans-deca-2,4-dienal (reactive carbonyl). The canonical activity was considerably reduced by all the conventional inhibitors (cybacron blue, triphenylthin chloride and bromosulfophthalein) and by other inhibitors (ellagic acid, alizarin and chenodeoxycholic acid). Besides this, rEgGST2-3 activity was inhibited by a number of anthelmintic drugs, where the halogenated phenolic drugs (mainly bithionol and hexachlorophene) acted as stronger inhibitors, suggesting they may bind to the EgGST2-3. Moreover, rEgGST2-3 exhibited glutathione-peroxidase activity, and its specific constant (k_cat/K_M) was calculated. Finally, rEgGST2-3 displayed the ability to bind non-substrate molecules, particularly anthelmintic drugs, suggesting that ligandin activity may have potential to act as a passive protection parasite mechanism. Overall, the rEgGST2-3 behavior was shown to be both complementary and redundant to that reported for rEgGST1, another characterized GST from E. granulosus. It would be appropriate that different enzymes in the same organism do not have exactly the same functional properties to develop a better adaptation to life in the host.

The Role of Xenobiotic-Metabolizing Enzymes in Anthelmintic Deactivation and Resistance in Helminths

Xenobiotic-metabolizing enzymes (XMEs) modulate the biological activity and behavior of many drugs, including anthelmintics. The effects of anthelmintics can often be abolished by XMEs when the drugs are metabolized to an inefficient compound. XMEs therefore play a significant role in anthelmintic efficacy. Moreover, differences in XMEs between helminths are reflected by differences in anthelmintic metabolism between target species. Taking advantage of the newly sequenced genomes of many helminth species, progress in this field has been remarkable. The present review collects up to date information regarding the most important XMEs (phase I and phase II biotransformation enzymes; efflux transporters) in helminths. The participation of these XMEs in anthelmintic metabolism and their possible roles in drug resistance are evaluated.

Purification of a recombinant glutathione transferase from the causative agent of hydatidosis, Echinococcus granulosus

This practical class activity was designed to introduce students to recombinant protein expression and purification. The principal goal is to shed light on basic aspects concerning recombinant protein production, in particular protein expression, chromatography methods for protein purification, and enzyme activity as a tool to evaluate purity and conformation of the recombinant product. Herein, we describe the purification of a glutathione transferase from the human parasite Echinococcus granulosus (EgGST1), the causative agent of hydatidosis. EgGST1 is expressed fused to a histidine tag and is purified by immobilized metal affinity chromatography. Protein quantification based on direct (UV absorbance) and indirect (colorimetric) methods are used and discussed. A simple colorimetric assay is used to measure GST activity and special emphasis is put on how to use these measurements to follow protein purification yields, its enrichment and its correct folding along the purification process. EgGST1 is easily expressed with high yields, purified in absence of protease inhibitors and proved to be robust concerning enzyme activity and protein integrity on a 1 week practical activity.