Molecular and biochemical characterizations of three fructose-1,6-bisphosphate aldolases from Clonorchis sinensis

A Comparative Analysis of the Protein Cargo of Extracellular Vesicles from Helminth Parasites

Helminth parasites cause debilitating-sometimes fatal-diseases in humans and animals. Despite their impact on global health, mechanisms underlying host-parasite interactions are still poorly understood. One such mechanism involves the exchange of extracellular vesicles (EVs), which are membrane-enclosed subcellular nanoparticles. To date, EV secretion has been studied in helminth parasites, including EV protein content. However, information is highly heterogeneous, since it was generated in multiple species, using varied protocols for EV isolation and data analysis. Here, we compared the protein cargo of helminth EVs to identify common markers for each taxon. For this, we integrated published proteomic data and performed a comparative analysis through an orthology approach. Overall, only three proteins were common in the EVs of the seven analyzed species. Additionally, varied repertoires of proteins with moonlighting activity, vaccine antigens, canonical and non-canonical proteins related to EV biogenesis, taxon-specific proteins of unknown function and RNA-binding proteins were observed in platyhelminth and nematode EVs. Despite the lack of consensus on EV isolation protocols and protein annotation, several proteins were shown to be consistently detected in EV preparations from organisms at different taxa levels, providing a starting point for a selective biochemical characterization.

Molecular characterization and immune efficacy of fructose-1,6-bisphosphate aldolase from Haemaphysalis longicornis (Acari: Ixodidae)

BACKGROUND

Ticks are obligate hematophagous ectoparasites that transmit a variety of pathogens to humans, wildlife and domestic animals. Vaccination is an effective and environmentally friendly method for tick control. Fructose-1,6-bisphosphate aldolase (FBA) is an important glycometabolism enzyme that is a candidate vaccine against parasites. However, the immune protection of FBA in ticks is unclear. METHODS AND RESULTS: The 1092-bp open reading frame (ORF) of FBA from Haemaphysalis longicornis (HlFBA), encoding a 363-amino acid protein, was cloned using PCR methodology. The prokaryotic expression vector pET32a(+)-HlFBA was constructed and transformed into cells of Escherichia coli BL21(DE3) strain for protein expression. The recombinant HlFBA protein (rHlFBA) was purified by affinity chromatography, and the western blot results suggested that the rHlFBA protein was immunogenic.

RESULTS

Results of the enzyme-linked immunosorbent assay showed that rabbits immunized with rHlFBA produced a humoral immune response specific to rHlFBA. A tick infestation trial indicated that, compared to the ticks in the histidine-tagged thioredoxin (Trx) group, the engorged tick weight and oviposition of female ticks and egg hatching rate of those in the rHlFBA group was reduced by 22.6%, 45.6% and 24.1%, respectively. Based on the cumulative effect of the these three parameters, the overall immune efficacy of rHlFBA was estimated to be 68.4%.

CONCLUSIONS

FBA is a candidate anti-tick vaccine that can significantly reduce the engorged tick weight, oviposition, and egg hatching rate. The use of enzymes involved in glucose metabolism is a new strategy in the development of anti-tick vaccines.

Characterization of Fructose-1,6-Bisphosphate Aldolase 1 of Echinococcus multilocularis

Glycolysis is one of the important ways by which Echinococcus multilocularis acquires energy. Fructose-1, 6-bisphosphate aldolase (FBA) plays an important role in this process, but it is not fully characterized in E. multilocularis yet. The results of genome-wide analysis showed that the Echinococcus species contained four fba genes (FBA1-4), all of which had the domain of FBA I and multiple conserved active sites. EmFBA1 was mainly located in the germinal layer and the posterior of the protoscolex. The enzyme activity of EmFBA1 was 67.42 U/mg with K_m and V_max of 1.75 mM and 0.5 mmol/min, respectively. EmFBA1 was only susceptible to Fe³⁺ but not to the other four ions (Na⁺, Ca²⁺, K⁺, Mg²⁺), and its enzyme activity was remarkably lost in the presence of 0.5 mM Fe³⁺. The current study reveals the biochemical characters of EmFBA1 and is informative for further investigation of its role in the glycolysis in E. multilocularis.

Multifunctional Fructose 1,6-Bisphosphate Aldolase as a Therapeutic Target

Fructose 1,6-bisphosphate aldolase is a ubiquitous cytosolic enzyme that catalyzes the fourth step of glycolysis. Aldolases are classified into three groups: Class-I, Class-IA, and Class-II; all classes share similar structural features but low amino acid identity. Apart from their conserved role in carbohydrate metabolism, aldolases have been reported to perform numerous non-enzymatic functions. Here we review the myriad "moonlighting" functions of this classical enzyme, many of which are centered on its ability to bind to an array of partner proteins that impact cellular scaffolding, signaling, transcription, and motility. In addition to the cytosolic location, aldolase has been found the extracellular surface of several pathogenic bacteria, fungi, protozoans, and metazoans. In the extracellular space, the enzyme has been reported to perform virulence-enhancing moonlighting functions e.g., plasminogen binding, host cell adhesion, and immunomodulation. Aldolase's importance has made it both a drug target and vaccine candidate. In this review, we note the several inhibitors that have been synthesized with high specificity for the aldolases of pathogens and cancer cells and have been shown to inhibit classical enzyme activity and moonlighting functions. We also review the many trials in which recombinant aldolases have been used as vaccine targets against a wide variety of pathogenic organisms including bacteria, fungi, and metazoan parasites. Most of such trials generated significant protection from challenge infection, correlated with antigen-specific cellular and humoral immune responses. We argue that refinement of aldolase antigen preparations and expansion of immunization trials should be encouraged to promote the advancement of promising, protective aldolase vaccines.

Amino acids serve as an important energy source for adult flukes of Clonorchis sinensis

Clonorchiasis, caused by chronic infection with Clonorchis sinensis (C. sinensis), is an important food-borne parasitic disease that seriously afflicts more than 35 million people globally, resulting in a socioeconomic burden in endemic regions. C. sinensis adults long-term inhabit the microaerobic and limited-glucose environment of the bile ducts. Energy metabolism plays a key role in facilitating the adaptation of adult flukes to crowded habitat and hostile environment. To understand energy source for adult flukes, we compared the component and content of free amino acids between C. sinensis-infected and uninfected bile. The results showed that the concentrations of free amino acids, including aspartic acid, serine, glycine, alanine, histidine, asparagine, threonine, lysine, hydroxylysine, and urea, were significantly higher in C. sinensis-infected bile than those in uninfected bile. Furthermore, exogenous amino acids could be utilized by adult flukes via the gluconeogenesis pathway regardless of the absence or presence of exogenous glucose, and the rate-limiting enzymes, such as C. sinensis glucose-6-phosphatase, fructose-1,6-bisphosphatase, phosphoenolpyruvate carboxykinase, and pyruvate carboxylase, exhibited high expression levels by quantitative real-time PCR analysis. Interestingly, no matter whether exogenous glucose was present, inhibition of gluconeogenesis reduced the glucose and glycogen levels as well as the viability and survival time of adult flukes. These results suggest that gluconeogenesis might play a vital role in energy metabolism of C. sinensis and exogenous amino acids probably serve as an important energy source that benefits the continued survival of adult flukes in the host. Our study will be a cornerstone for illuminating the biological characteristics of C. sinensis and the host-parasite interactions.

Clonorchiasis, closely related to cholangiocarcinoma and hepatocellular carcinoma, has led to a negative socioeconomic impact in global areas especially some Asian endemic regions. Owing to the emergence of drug resistance and hypersensitivity reactions after the massive and repeated use of praziquantel as well as the lack of effective vaccines, searching for new strategies that prevent and treat clonorchiasis has become an urgent matter. Clonorchis sinensis, the causative agent of clonorchiasis, long-term inhabits the microaerobic and limited-glucose environment of the bile ducts. Adequate nutrients are essential for adult flukes to resist the adverse condition and survive in the crowed habitat. Studies on energy metabolism of adult flukes are beneficial for further exploring host-parasite interactions and developing novel anti-parasitic drugs. Our results suggest that gluconeogenesis probably plays a vital role in energy metabolism of Clonorchis sinensis and exogenous amino acids might be an essential energy source for adult flukes to successfully survive in the host. Our foundational study opens a new avenue for explaining energy metabolism of Clonorchis sinensis and provides a valuable strategy that the gluconeogenesis pathway will be a potential and novel target for the prevention and treatment of clonorchiasis.

Clonorchis sinensis and clonorchiasis

Clonorchis sinensis is a fish-borne trematode that inhabits the bile duct of mammals including humans. Clonorchiasis is prevalent in China, Korea, and Vietnam, and 15-20 million people are estimated to be infected by this fluke. Freshwater snails act as the first intermediate host for the proliferation of C. sinensis larvae and shed the cercariae into water. The cercariae penetrate the skin of freshwater fish and transform to metacercariae. Humans are infected by eating raw or undercooked freshwater fish as dishes of filet, "sashimi," or congee, which contain C. sinensis metacercariae. In humans, the C. sinensis metacercariae excyst in the duodenum, and juvenile flukes migrate up via bile chemotaxis into bile ducts. Once there, C. sinensis provokes hyperplasia of the bile duct epithelium, obstructive jaundice, ascites, liver enlargement and cirrhosis, and infrequent cholangiocarcinoma (CCA). Although the association between C. sinensis infection and CCA has been firmly established in past decades, the underlying mechanisms are not elucidated in detail. In the context of chronic clonorchiasis-associated hepatobiliary aberrations, the constitutive disruption of redox homeostasis and dysregulation of physiological signaling pathways may promote the malignant transformation of cholangiocytes, thus leading to substantial acquisition of a more aggressive phenotype by these cells: CCA. With advances of genomic and molecular biological approaches, diverse C. sinensis proteins that are essential for parasite physiology and pathogenicity have been identified and characterized. Some of the proteins have been considered as attractive targets for development of vaccines and chemotherapeutics. Candidate antigens for reliable serodiagnosis of clonorchiasis have been studied.

Protein extract from head-foot tissue of Oncomelania hupensis promotes the growth and development of mother sporocysts of Schistosoma japonicum via upregulation of parasite aldolase gene

Previous studies showed that protein extract from head-foot tissue of Oncomelania hupensis (O. hupensis) (PhfO), when cocultured with mother sporocysts of Schistosoma japonicum (S. japonicum), was beneficial for parasite's growth and development but the underlying mechanisms remain unclear. One possible strategy for PhfO to promote the growth and development of mother sporocysts of S. japonicum is to upregulate parasite's survival genes. Fructose-1,6-bisphosphate aldolase (ALD), an essential enzyme of glycometabolism in the energy metabolism process, plays an important role in the survival and the growth and development of schistosomes. Using an in vitro coculture system, in this study, we analyzed the potential involvement of the ald gene in the growth and development of mother sporocysts of S. japonicum following coculture with PhfO. We found that coculture with PhfO promoted the growth and development and the survival of mother sporocysts, and increased parasites' ATP consumption level. Mother sporocysts cocultured with PhfO showed a significantly increased expression of the ald gene at both RNA and protein levels. The ALD protein mainly expressed in the cytoplasm of mother sporocysts. Knockdown of ald gene in parasites decreased the ALD protein expression and the ATP consumption level, suppressed the growth and development, and attenuated the survival of mother sporocysts. In ald knockdown mother sporocysts, the effects of PhfO on the ALD expression, the ATP consumption level, the growth and development, and the survival of larvae were significantly abolished. Therefore, the data suggest that PhfO could promote the growth and development, and the survival of mother sporocysts of S. japonicum via upregulating the expression of the ald gene.

Molecular Characterization of Fructose-1,6-bisphosphate Aldolase From Trichinella spiralis and Its Potential in Inducing Immune Protection

Trichinella spiralis is a major food-borne parasite worldwide. Trichinellosis caused by T. spiralis is not only a public health problem, but also an economic hazard in food safety. The development of effective vaccines to prevent Trichinella infection in domestic animals and humans is urgently needed for controlling of this zoonosis. Fructose-1, 6-bisphosphate aldolase (FBPA) is involved in energy production in glycolysis and is also associated with many non-glycolysis functions in the parasite, such as adhesion to host cells, plasminogen binding, and invasion. FBPA has been considered as a potential vaccine candidate or as a target for chemotherapeutic treatment. Here, we report for the first time the characterization of FBPA of T. spiralis and an evaluation of its potential as a vaccine candidate antigen against T. spiralis infection in mice. The results of qPCR and western blot analysis showed that the Ts-FBPA gene was expressed at various developmental stages of T. spiralis and was also detected in excretory–secretory products (ES) of T. spiralis muscle larvae (ML). Immunostaining with anti-Ts-FBPA mouse sera indicated that it localized principally to the surface and embryos of this parasitic nematode. Vaccination of mice with recombinant Ts-FBPA (rTs-FBPA) resulted in a Th1/Th2 mixed humoral and cellular immune response with Th2 predominant, as well as remarkably elevated IgE levels. Moreover, mice vaccinated with rTs-FBPA displayed a 48.7% reduction in adult worm burden and 52.5% reduction in muscle larval burden. These studies indicated that Ts-FBPA is a promising target for developing an effective vaccine to prevent and control Trichinella infection.

Immunosuppression, oxidative stress, and glycometabolism disorder caused by cadmium in common carp (Cyprinus carpio L.): Application of transcriptome analysis in risk assessment of environmental contaminant cadmium

Cadmium (Cd), a hazardous environmental contaminant with irreversible toxicity to fish, has been detected in aquatic environment of many countries. The common carp is one of the most widely distributed fish in the world, so we used common carp to assess environmental contaminant risk. In present study, we investigated effects of Cd on immune function, oxidative defense, and glycometabolism in the spleens of common carp by transcriptome analysis. Obtained 3794 differentially expressed genes (including 1848 up-regulated and 1946 down-regulated genes) were enriched using databases of Kyoto Encyclopedia of Genes and Genomes, and Gene Ontology in David bioinformatics software (version 6.8). The pathways and gene functions of immune, oxidative defense, and glycometabolism were obtained and identified. Some relative genes were validated using qRT-PCR and gene expression of IL-1β, INF-γ, IL-6, Cxcl18b, HO-1a, CAT, GPx1, GCK, and FBA decreased; and gene expression of B4GALT1, GPAT3, and CYP26B1 increased. Our results indicated that Cd exposure led to immunosuppression, oxidative stress, and glycometabolism disorder in the common carp spleens. The present study gives a novel insight and method on environmental risk assessment.

Characterization and localization of Opisthorchis viverrini fructose-1,6-bisphosphate aldolase

Opisthorchis viverrini (Ov) infection is a long-time public health problem in Thailand that can lead to bile duct cancer, cholangiocarcinoma (CCA). Characterization of the Ov proteins at a molecular level will increase our knowledge of host-parasite interaction that can be applied to new drug, vaccine, or immunodiagnostic development. In this study, an important enzyme in the Ov glycolytic pathway, fructose-1,6-bisphosphate aldolase (FBPA), that had been obtained from a previous study was characterized and immunolocalized. The full-length sequence of OvFBPA gene is 1089bp and encodes 362 amino acids with a predicted molecular weight and isoelectric point of 39.54kDa and 7.61, respectively. Additionally, three OvFBPA isoforms were identified by sequence analysis. The amino acid sequence of OvFBPA-1 characterized in this study shared 98% identity to FBPA isoform 1 of Clonorchis sinensis that was classified based on highly conserved active residues to class-I FBPA. The recombinant OvFBPA-1 protein was expressed as a soluble form in Escherichia coli at 25°C with N-terminal His-tagged fusion protein and the purified OvFBPA-1 protein was used to generate polyclonal antibody in mice. Antibody against rOvFBPA-1 protein was able to detect the native OvFBPA-1 protein in both Ov infected hamster liver section and Ov excretory-secretory (ES) products by immunohistochemistry and western blotting, respectively.