Molecular cloning and immunological characterization of phosphoglycerate kinase from Clonorchis sinensis

A reanalysis and integration of transcriptomics and proteomics datasets unveil novel drug targets for Mekong schistosomiasis

Schistosomiasis, caused by Schistosoma trematodes, is a significant global health concern, particularly affecting millions in Africa and Southeast Asia. Despite efforts to combat it, the rise of praziquantel (PZQ) resistance underscores the need for new treatment options. Protein kinases (PKs) are vital in cellular signaling and offer potential as drug targets. This study focused on focal adhesion kinase (FAK) as a candidate for anti-schistosomal therapy. Transcriptomic and proteomic analyses of adult S. mekongi worms identified FAK as a promising target due to its upregulation and essential role in cellular processes. Molecular docking simulations assessed the binding energy of FAK inhibitors to Schistosoma FAK versus human FAK. FAK inhibitor 14 and PF-03814735 exhibited strong binding to Schistosoma FAK with minimal binding for human FAK. In vitro assays confirmed significant anti-parasitic activity against S. mekongi, S. mansoni, and S. japonicum, comparable to PZQ, with low toxicity in human cells, indicating potential safety. These findings highlight FAK as a promising target for novel anti-schistosomal therapies. However, further research, including in vivo studies, is necessary to validate efficacy and safety before clinical use. This study offers a hopeful strategy to combat schistosomiasis and reduce its global impact.

Identification of novel biomarkers for anti-Toxoplasma gondii IgM detection and the potential application in rapid diagnostic fluorescent tests

Toxoplasmosis, while often asymptomatic and prevalent as a foodborne disease, poses a considerable mortality risk for immunocompromised individuals during pregnancy. Point-of-care serological tests that detect specific IgG and IgM in patient sera are critical for disease management under limited resources. Despite many efforts to replace the T. gondii total lysate antigens (TLAs) by recombinant antigens (rAgs) in commercial kits, while IgG detection provides significant specificity and sensitivity, IgM detection remains comparatively low in sensitivity. In this study, we attempted to identify novel antigens targeting IgM in early infection, thereby establishing an IgM on-site detection kit. Using two-dimensional gel electrophoresis (2DE) and mouse serum immunoblotting, three novel antigens, including EF1γ, PGKI, and GAP50, were indicated to target T. gondii IgM. However, rAg EF1γ was undetectable by IgM of mice sera in Western blotting verification experiments, and ELISA coated with PGKI did not eliminate cross-reactivity, in contrast to GAP50. Subsequently, the lateral flow reaction employing a strip coated with 0.3 mg/mL purified rAg GAP50 and exhibited remarkable sensitivity compared with the conventional ELISA based on tachyzoite TLA, which successfully identified IgM in mouse sera infected with tachyzoites, ranging from 103 to 104 at 5 dpi and 104 at 7 dpi, respectively. Furthermore, by using standard T. gondii-infected human sera from WHO, the limit of detection (LOD) for the rapid fluorescence immunochromatographic test (FICT) using GAP50 was observed at 0.65 IU (international unit). These findings underline the particular immunoreactivity of GAP50, suggesting its potential as a specific biomarker for increasing the sensitivity of the FICT in IgM detection.

Functional characterization of Clonorchis sinensis sodium-bile acid co-transporter (CsSBAT) as a steroid sulfate transporter

Clonorchis sinensis (Cs) is a common trematode in Asian countries. Infection by Cs can result in many clinical symptoms. Here, a cDNA encoding a Cs apical sodium-dependent bile acid transporter (CsSBAT) was isolated from a Cs cDNA library, and functional characterization was performed using Xenopus laevis oocyte expression system. When expressed in Xenopus laevis oocytes, CsSBAT mediated the transport of radiolabeled estrone sulfate and dehydroepiandrosterone sulfate. No trans-uptake of carnitine, estradiol 17 β-D glucuronide, prostaglandin E₂, p-aminohippuric acid, α-ketoglutaric acid, and tetraethylammonium was observed. CsSBAT-mediated estrone sulfate uptake was in a time- and sodium-dependent manner. CsSBAT showed no exchange properties in efflux experiments. Concentration-dependent results showed saturable kinetics consistent with the Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 0.3 ± 0.04 μM for [³H]estrone sulfate. CsSBAT-mediated estrone sulfate uptake was strongly inhibited by sulfate conjugates but not glucuronide conjugates. These findings contribute to our understanding of CsSBAT transport properties and the cascade of estrogen metabolite movement in Cs.

Serodiagnostic antigens of Clonorchis sinensis identified and evaluated by high-throughput proteogenomics

Clonorchiasis caused by Clonorchis sinensis is endemic in East Asia; approximately 15 million people have been infected thus far. To diagnose the infection, serodiagnostic tests with excellent functionality should be performed. First, 607 expressed sequence tags encoding polypeptides with a secretory signal were expressed into recombinant proteins using an in vitro translation system. By protein array-based screening using C. sinensis-infected sera, 18 antigen candidate proteins were selected and assayed for cross-reactivity against Opisthorchis viverrini-infected sera. Of the six antigenic proteins selected, four were synthesized on large scale in vitro and evaluated for antigenicity against the flukes-infected human sera using ELISA. CsAg17 antigen showed the highest sensitivity (77.1%) and specificity (71.2%). The sensitivity and specificity of the bacterially produced CsAg17-28GST fusion antigen was similar to those of CsAg17 antigen. CsAg17 antigen can be used to develop point-of-care serodiagnostic tests for clonorchiasis.

Human clonorchiasis is a parasitic disease caused by the Chinese liver fluke, Clonorchis sinensis. Humans are infected through eating raw freshwater fishes carrying C. sinensis metacercariae, the encysted larvae. They excyst in the duodenum, move into the liver via bile duct and grow to adult worms. Excretory-secretory products of the worm damage the liver causing various inflammatory pathological changes and may lead to bile duct cancer. Although there exists an anthelmintic choice praziquantel to kill the fluke, emphasis is placed on early diagnosis and prevention before the infection becomes disease. Microscopic stool examination is the standard diagnostic method but is cumbersome and time consuming. Blood serum antibodies from clonorchiasis patients could provide a simple and fast diagnosis. However, antibody detecting diagnostics developed so far have a low specificity and sensitivity. In the present study we selected 607 antigenic candidate proteins from the genomic database and synthesized them through an integrated high-throughput proteogenomic tools. We identified several antigenic proteins and evaluated their diagnostic potential for clonorchiasis. One of them, CsAg17, showed a high sensitivity and specificity. This antigen deserves development of point-of-care serodiagnostics for C. sinensis infections.

Sodium-bile acid co-transporter is crucial for survival of a carcinogenic liver fluke Clonorchis sinensis in the bile

The liver fluke Clonorchis sinensis inhabits the bile ducts, where bile concentration disparities across the fluke cell membrane can cause bile intoxication. Sodium-bile acid co-transporter (SBAT) plays a crucial role in bile acid recycling. The process by which SBAT imports bile acids is electrically coupled to sodium ion co-transportation. Here, we report that the SBAT of C. sinensis (CsSBAT) is involved in bile acid transportation. CsSBAT cDNA encoded a putative polypeptide of 546 amino acid residues. Furthermore, CsSBAT consisted of ten putative transmembrane domains, and its 3D structure was predicted to form panel and core domains. The CsSBAT had one bile acid- and three Na⁺-binding sites, enabling coordination of a symport process. CsSBAT was mainly localized in the mesenchymal tissue throughout the fluke body and sparsely localized in the basement of the tegument, intestinal epithelium, and excretory bladder wall. Bile acid permeated into the adult flukes in a short time and remained at a low concentration level. Bile acid accumulated inside the mesenchymal tissue when CsSBAT was inhibited using polyacrylic acid–tetradeoxycholic acid conjugate. The accumulated bile acid deteriorated the C. sinensis adults leading to death. CsSBAT silencing shortened the lifespan of the fluke when it was placed into bile. Taken together, we propose that CsSBAT transports bile acids in the mesenchymal tissue and coordinate with outward transporters to maintain bile acid homeostasis of C. sinensis adults, contributing to C. sinensis survival in the bile environment.

Clonorchiasis is a neglected tropical disease caused by infection with the liver fluke Clonorchis sinensis. C. sinensis is a biological carcinogen causing cholangiocarcinoma in humans. Juvenile worms inhabit and grow to adults in the bile ducts. Bile acids in the bile are double-edged molecules; they promote metabolism, but differences in their concentration across the cell membrane could lead to bile intoxication. The sodium-bile acid co-transporter of C. sinensis (CsSBAT) is indispensable for maintaining its normal physiology and bile detoxification in the bile duct. However, information related to the molecular and biological characteristics of the SBAT of liver flukes is not available. Here, we cloned CsSBAT for the first time in trematodes and characterized its tertiary structure and physiological functions. The sequential and structural properties of CsSBAT were similar to the apical sodium-bile acid co-transporter found in mammalian intestines. CsSBAT shared a mesenchymal tissue distribution with Na⁺-taurocholate co-transporting polypeptide in the hepatocytes adjacent to the bile ducts. Bile acids accumulated in C. sinensis adults when CsSBAT was inhibited, causing their death. This information might promote further studies on the physiological functions of SBAT and other trematode bile transporters and open new avenues toward developing novel anthelminthic drugs.

Identification and characterization of cytosolic malate dehydrogenase from the liver fluke Fasciola gigantica

The liver fluke zoonoses, Fasciola spp. are parasitic helminths infecting humans and animals globally. Recent sequencing of the genome of Fasciola gigantica has provided a basis to understand the biochemistry of this parasite. Here, we identified the cytosolic malate dehydrogenase in F. gigantica (FgMDH) and characterized the enzyme biochemically and structurally. F. gigantica encodes a single cytosolic MDH, a key enzyme of the citric acid cycle. It catalyzes the reversible oxidation of malate to oxaloacetate using NAD⁺. The Fgmdh gene was amplified and cloned for expression of the recombinant protein. The purified protein showed a molecular weight of ~ 36 kDa that existed in a dimeric form in solution. The recombinant enzyme was catalytically active as it catalyzed both forward and reverse reactions efficiently. The kinetic parameters were determined for both directions. The structure of FgMDH and human MDH were modeled and validated. The superimposition of both the model structures showed overall structural similarity in the active site loop region, however, the conformation of the residues was different. Molecular docking elucidated the binding sites and affinities of the substrates and cofactors to the enzyme. Simulation of molecular dynamics and principal component analysis indicated the stability of the systems and collective motions, respectively. Understanding the structural and functional properties of MDH is important to better understand the roles of this enzyme in the biochemistry of the parasite.

Dopaminergic antagonists inhibit bile chemotaxis of adult Clonorchis sinensis and its egg production

Human clonorchiasis, caused by Clonorchis sinensis, is endemic in East Asian countries. C. sinensis metacercariae excyst in the duodenum of mammalian hosts, migrate to the intrahepatic bile duct, and mature into adults in the milieu of bile. We have previously shown that newly excysted juvenile C. sinensis move chemotactically toward bile and bile acids. Here, the chemotactic behavior of adult C. sinensis (CsAd) toward bile and bile acids was investigated. CsAds moved toward 0.05-5% bile and were most attracted to 0.5% bile but moved away from 10% bile. Upon exposure to 1-10% bile, CsAds eventually stopped moving and then died quickly. Among bile acids, CsAds showed strong chemotaxis toward cholic acid (CA) and deoxycholic acid. On the contrary, CsAds repelled from lithocholic acid (LCA). Moreover, at higher than 10 mM LCA, CsAds became sluggish and eventually died. Dopamine D1 receptor antagonists (LE-300 and SKF-83566), D2/3 receptor antagonists (raclopride and its derivative CS-49612), and a dopamine re-uptake inhibitor inhibited CA-induced chemotaxis of CsAds almost completely. Clinically used antipsychotic drugs, namely chlorpromazine, haloperidol, and clozapine, are dopaminergic antagonists and are secreted into bile. They completely inhibited chemotaxis of CsAds toward CA. At the maximum doses used to treat patients, the three tested medicines only expelled 2-12% of CsAds from the experimentally infected rabbits, but reduced egg production by 64-79%. Thus, antipsychotic medicines with dopaminergic antagonism could be considered as new anthelmintic candidates for human C. sinensis infections.

Characterization and role of PGK from Litopenaeus vannamei in WSSV infection

Phosphoglycerate kinase (EC 2.7.2.3, PGK) catalyses the reversible transfer of a phosphate group from 1,3-diphosphoglyceric acid and ADP to produce 3-phosphoglyceric acid and ATP, which represents the initial production of ATP during glycolysis; therefore, PGK is a key enzyme in the energy metabolism. To study the role of PGK in the resistance to WSSV infection in shrimp, the full-length cDNA of the PGK gene (LvPGK) from Litopenaeus vannamei was obtained by using homology cloning and RACE amplification. The tissue distribution of LvPGK and its expression changes in the main immune tissues after WSSV stimulation were obtained by quantitative real-time PCR. Furthermore, RNA interference (RNAi) was used to study the role of LvPGK in shrimp defending against WSSV infection. The results showed that the full-length cDNA sequence of LvPGK was 1855 bp, contained a 1248 bp open reading frame (ORF) encoding 415 amino acids, and included a conserved PGK domain. LvPGK presented ubiquitous expression in most examined tissues, with the most predominant expression in the muscle and the weakest expression in the intestine. LvPGK transcripts could be induced in the hemocytes and hepatopancreas by injection with WSSV. Both the replication of WSSV and the shrimp cumulative mortality decreased significantly after LvPGK knockdown (P < 0.01). After challenging LvPGK RNAi shrimp with WSSV, the concentration of glucose in the hepatopancreas and muscle tissue did not show significant change; however, the content of pyruvate and lactate decreased significantly (P < 0.05). Moreover, significant decreases in the expression levels of crustin, ALF1, ALF2 and ALF3 were also detected. The results suggested that LvPGK might be involved in WSSV replication by increasing host aerobic and anaerobic metabolism.

Characterization of filarial phosphoglycerate kinase

Phosphoglycerate kinase (PGK) is a key enzyme of glycolysis which also acts as a mediator of DNA replication and repair in the nucleus. We have cloned and expressed PGK in Brugia malayi. The rBmPGK was found to be 415 amino acid residues long having 45 kDa subunit molecular weight. This enzyme was also identified in different life stages of bovine filarial parasite Setaria cervi. The enzyme activity was highest in microfilarial stage followed by adult female and male as also shown by real time PCR in the present study. Further using BmPGK primers the cDNA prepared from S. cervi was amplified and sequenced which showed 100% homology with Brugia malayi PGK. B. malayi and S. cervi, PGK consists of conserved calmodulin binding domain (CaMBD) having 21 amino acids. In the present study we have shown the CaMBD binds to calcium-calmodulin and regulates its activity. The binding of calmodulin (CaM) with CaMBD was confirmed using calmodulin agarose binding pull down assay, which showed that the rBmPGK binds to CaM agarose-calcium dependent manner. The effect of CaM-Ca²⁺on the activity of rBmPGK was studied at different concentration of CaM (0.01-5.0 μM) and calcium chloride (0.01-100 μM). The rBmPGK was activated up to 85% in the presence of CaM at 1 μM and 10 μM concentration of CaCl₂. Interestingly this activation was abrogated by metal chelator EDTA. Similar results were shown in case of Setaria cervi PGK. A significant increase (90 ± 10) % in ScPGK activity was observed in the presence of CaM and CaCl₂ at 1.0 μM and 1.0 mM respectively, further increase in the conc. of CaCl₂, the activity of ScPGK was found to be decreased like rBmPGK. Bioinformatics studies have also confirmed the interaction between CaMBD and CaM which showed CaM interacted to Phe 206, Gln 220, Arg 223 and Asn 224 of rBmPGK CaM binding domain. On the basis of these findings, it has been suggested that the activity of filarial PGK could be regulated in cells by Ca²⁺-CaM depending upon the concentration of calcium. To the best of our knowledge this is first report in filarial parasite.

Chemotactic migration of newly excysted juvenile Clonorchis sinensis is suppressed by neuro-antagonists

The metacercariae of the Clonorchis sinensis liver fluke excyst in the duodenum of mammalian hosts, and the newly excysted juveniles (CsNEJs) migrate along the bile duct via bile chemotaxis. Cholic acid is a major component of bile that induces this migration. We investigated the neuronal control of chemotactic behavior of CsNEJs toward cholic acid. The migration of CsNEJs was strongly inhibited at sub-micromolar concentration by dopamine D1 (LE-300 and SKF-83566), D2 (spiramide, nemonapride, and sulpiride), and D3 (GR-103691 and NGB-2904) receptor antagonists, as well as a dopamine reuptake inhibitor (BTCP). Neuropeptides, FMRFamide, peptide YY, and neuropeptide Y were also potent inhibitors of chemotaxis. Meanwhile, serotonergic, glutamatergic, and cholinergic inhibitors did not affect chemotaxis, with the exception of fluoxetine and CNQX. Confocal immunofluorescence analysis indicated that dopaminergic and cholinergic neurons were colocalized in the somatic muscle tissues of adult C. sinensis. Our findings suggest that dopaminergic neurons and neuropeptides play a major role in the chemotactic migration of CsNEJs to bile, and their inhibitors or modulators could be utilized to prevent their migration from the bile duct.

Liver Flukes: Clonorchis and Opisthorchis

Clonorchis sinensis, Opisthorchis viverrini, and O. felineus are liver flukes of human and animal pathogens occurring across much of Europe and Asia. Nevertheless, they are often underestimated compared to other, better known neglected diseases in spite of the fact that many millions of people are infected and hundreds of millions are at risk. This is possibly because of the chronic nature of the infection and disease and that it takes several decades prior to a life-threatening pathology to develop. Several studies in the past decade have provided more information on the molecular biology of the liver flukes which clearly lead to better understanding of parasite biology, systematics, and population genetics. Clonorchiasis and opisthorchiasis are characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. These chronic inflammations eventually lead to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in some infected individuals. In Thailand alone, opisthorchiasis-associated CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce hepatobiliary morbidity and CCA, the primary intervention measures focus on control and elimination of the liver fluke. Accurate diagnosis of liver fluke infections in both human and other mammalian, snail and fish intermediate hosts, are important for achieving these goals. While the short-term goal of liver fluke control can be achieved by praziquantel chemotherapy, a comprehensive health education package targeting school children is believed to be more beneficial for a long-term goal/solution. It is recommended that a transdisciplinary research or multisectoral control approach including one health and/or eco health intervention strategy should be applied to combat the liver flukes, and hence contribute to reduction of cholangiocarcinoma in endemic areas.

Bile acids drive chemotaxis of Clonorchis sinensis juveniles to the bile duct

Clonorchiasis is a neglected tropical disease caused by Chinese liver fluke, Clonorchis sinensis infection. C. sinensis is a biological carcinogen causing cholangiocarcinoma in humans. In the mammalian host, C. sinensis newly excysted juveniles (CsNEJs) migrate from the duodenum into the bile duct. Bile drives the chemotactic behavior of CsNEJs. Little is known about which components of bile induce the chemotaxis. We designed a chemotaxis assay panel and measured the chemotactic behavior of CsNEJs in response to bile or bile acids. The CsNEJs migrated toward 0.1–1% bile but away from 5–10% bile. The CsNEJs showed strong chemoattraction to cholic acid ≥25 mM, but chemorepulsion to lithocholic acid ≥0.25 mM. To the CsNEJs, mixture of cholic acid and lithocholic acid was chemoattractive at a ratio greater than 25:1 but chemorepulsive at one smaller than that. Regarding migration in the mammalian hosts, high concentration of lithocholic acid in the gallbladder bile may repel CsNEJs from entering it. However, bile in the hepatic bile duct has a chemoattractive strength of cholic acid but a trace amount of lithocholic acid. Collectively, our results explain why the CsNEJs migrate principally to the hepatic bile ducts, bypassing the gallbladder.

We previously reported that Clonorchis sinensis newly excysted juveniles (CsNEJs) were chemotactically attracted to bile. However, there is still a paucity of information regarding which components and what concentration of bile induce the chemotactic behavior. Here, we show, among various bile components tested, two have opposing chemotactic influences on the CsNEJs; cholic acid was characterized as a chemoattractant and lithocholic acid as a chemorepellent. Chemorepulsive migration was dependent on the concentration of lithocholic acid. Notably, the ratio (25:1) of cholic acid and lithocholic acid plays a critical role in defining chemotactic preferences of CsNEJs. We suspect that this bile acid ratio directs the parasites in the mammalian host, i.e. the high concentration of lithocholic acid in the gallbladder bile may repel CsNEJs from entering it. Bile in the hepatic bile duct has a chemoattractive level of cholic acid but a trace amount of lithocholic acid. These findings may explain why the CsNEJs preferentially migrate to the common and hepatic bile ducts rather than the gallbladder. Deeper understanding on the parasitism of the liver fluke is likely to have major implications for the studies on other parasites.

Cs1, a Clonorchis sinensis-derived serodiagnostic antigen containing tandem repeats and a signal peptide

Background

Clonorchiasis, caused by the liver fluke Clonorchis sinensis, remains a serious public health issue in Asia, especially in China, and its relationship with cholangiocarcinoma has highlighted the importance of C. sinensis infection. Proteins containing tandem repeats (TRs) are found in a variety of parasites and, as targets of B-cell responses, are valuable for the serodiagnosis of parasite infections. Here, we identified a novel C. sinensis-specific antigen, Cs1, containing TRs, and investigated its diagnostic value, other immunological properties, and tissue distribution.

Methodology/Principal findings

A partial Cs1 cDNA sequence was cloned by screening an adult C. sinensis cDNA expression library. The full-length Cs1 cDNA was obtained by 5′ rapid amplification of cDNA ends. The deduced Cs1 protein consists of a signal peptide and five TRs of 21 amino acids. The recombinant Cs1 (rCs1) was constructed and purified. rCs1 showed higher sensitivity (94.3%) and specificity (94.4%) than the C. sinensis excretory–secretory products (ESPs) according to ELISA of 114 serum samples. Native Cs1 was identified in C. sinensis ESPs and crude antigens of adult C. sinensis by western blotting using an anti-rCs1 monoclonal antibody. ELISA of recombinant peptides of different Cs1 regions demonstrated that the TR region was immunodominant in Cs1. Immunohistochemistry and confocal microscopy revealed that Cs1 is located in a granule-like structure surrounding the acetabulum of C. sinensis adults that has not previously been described.

Conclusions/Significance

We identified a novel C. sinensis-specific TR protein, Cs1, which is an antigen of high serological significance, compared with C. sinensis ESPs. The deduced features of Cs1 show a unique structure containing TRs and a signal peptide and the TR region is immunodominant in Cs1. This provides a basis for targeted screens of other antigens. The novel structure in which Cs1 is located also deserves further investigation.

Clonorchiasis is a neglected tropical disease. The major factor that prevents the effective management of clonorchiasis is a lack of effective diagnostic tools. Proteins containing tandem repeats (TRs), which have been found in a variety of parasites, are known targets of B-cell responses and can be useful for the serodiagnosis of parasite infections. Here we identified a novel C. sinensis-specific cDNA, which we named Cs1. This cDNA encodes a protein that has a unique structure, containing TRs and a signal peptide. A recombinant Cs1 protein (rCs1) was expressed and purified. rCs1 showed a high sensitivity and specificity in enzyme-linked immunosorbent assays, and lower cross-reactivity with Paragonimus westermani compared with C. sinensis excretory–secretory products. Our results also indicated that the TR region was immunodominant in the Cs1 protein. Immunohistochemistry and confocal microscopy revealed that Cs1 was located in a granule-like structure surrounding the acetabulum of adult worms that has not been previously described in C. sinensis. These results show that Cs1 is a promising antigen for serodiagnosis of clonorchiasis and its features provide a basis for future targeted screens of entire proteomes based on the likelihood of seroreactivity.

Current Perspectives on Opisthorchiasis Control and Cholangiocarcinoma Detection in Southeast Asia

Similar to bile duct cancer or cholangiocarcinoma (CCA) in the western world, opisthorchiasis-associated CCA in Southeast Asia is an aggressive cancer with high mortality rates. It is known to cause a significant health burden in the opisthorchiasis region in Thailand and possibly throughout mainland Southeast. To reduce this health burden, a comprehensive prevention and control program for opisthorchiasis, as well as CCA, is required. In this review, our aim is to provide a brief update of the current situation regarding the natural history of opisthorchiasis and health burden of CCA in Southeast Asia. A comprehensive approach to tackling these issues being implemented in Thailand under the “Cholangiocarcinoma Screening and Care Program” is described. This comprehensive program consists of a three stage prevention and patient care program. The primary prevention component involves opisthorchiasis screening using a new and sensitive urine assay. The secondary prevention component involves screening for CCA and periductal fibrosis, with suspected CCA patients following the protocol for confirmation and appropriate treatment. Due to the eco-epidemiology of opisthorchiasis-induced CCA, the anticipated impacts and outcomes of the program include short-, medium-, and the long-term goals for the reduction of CCA incidence. To achieve long-term sustainable impacts, concerted efforts to raise social awareness and participating action by general public, non-government organizations, and government agencies are necessary. The strategic plans developed for this program can be expanded for use in other endemic areas as well as being a model for use in other chronic diseases.

Sequence analysis and characterization of pyruvate kinase from Clonorchis sinensis, a 53.1-kDa homopentamer, implicated immune protective efficacy against clonorchiasis

BACKGROUND

Clonorchis sinensis, the causative agent of clonorchiasis, is classified as one of the most neglected tropical diseases and affects more than 15 million people globally. This hepatobiliary disease is highly associated with cholangiocarcinoma. As key molecules in the infectivity and subsistence of trematodes, glycolytic enzymes have been targets for drug and vaccine development. Clonorchis sinensis pyruvate kinase (CsPK), a crucial glycolytic enzyme, was characterized in this research.

RESULTS

Differences were observed in the sequences and spatial structures of CsPK and PKs from humans, rats, mice and rabbits. CsPK possessed a characteristic active site signature (IKLIAKIENHEGV) and some unique sites but lacked the N-terminal domain. The predicted subunit molecular mass (Mr) of CsPK was 53.1 kDa. Recombinant CsPK (rCsPK) was a homopentamer with a Mr. of approximately 290 kDa by both native PAGE and gel filtration chromatography. Significant differences in the protein and mRNA levels of CsPK were observed among four life stages of C. sinensis (egg, adult worm, excysted metacercaria and metacercaria), suggesting that these developmental stages may be associated with diverse energy demands. CsPK was widely distributed in adult worms. Moreover, an intense Th1-biased immune response was persistently elicited in rats immunized with rCsPK. Also, rat anti-rCsPK sera suppressed C. sinensis adult subsistence both in vivo and in vitro.

CONCLUSIONS

The sequences and spatial structures, molecular mass, and expression profile of CsPK have been characterized. rCsPK was indicated to be a homopentamer. Rat anti-rCsPK sera suppressed C. sinensis adult subsistence both in vivo and in vitro. CsPK is worthy of further study as a promising target for drug and vaccine development.

Molecular cloning, purification and characterization of Brugia malayi phosphoglycerate kinase

Phosphoglycerate kinase (PGK) is a glycolytic enzyme present in many parasites. It has been reported as a candidate molecule for drug and vaccine developments. In the present study, a full-length cDNA encoding the Brugia malayi 3-phosphoglycerate kinase (BmPGK) with an open reading frame of 1.3 kb was isolated and PCR amplified and cloned. The exact size of the BmPGK's ORF is 1377 bps. The BmPGK gene was subcloned into pET-28a (+) expression vector, the expressed enzyme was purified by affinity column and characterized. The SDS-PAGE analysis revealed native molecular weight of recombinant Brugia malayi 3-phosphoglycerate kinase (rBmPGK) to be ∼45 kDa. The enzyme was found sensitive to temperature and pH, it showed maximum activity at 25 °C and pH 8.5. The K_m values for PGA and ATP were 1.77 and 0.967 mM, respectively. The PGK inhibitor, clorsulon and antifilarial drugs albendazole and ivermectin inhibited the enzyme. The specific inhibitor of PGK, clorsulon, competitively inhibited enzyme with K_i value 1.88 μM. Albendazole also inhibited PGK competitively with K_i value 35.39 μM. Further these inhibitory studies were confirmed by docking and molecular simulation of drugs with enzyme. Clorsulon interacted with substrate binding site with glutamine 37 as well as in hinge regions with aspartic acid 385 and valine 387 at ADP binding site. On the other hand albendazole interacted with asparagine 335 residues. These effects were in good association with binding interactions. Thus current study might help in designing and synthesis of effective inhibitors for this novel drug target and understanding their mode of interaction with the potent anthelmintic drugs.

Molecular and structural characteristics of multidrug resistance-associated protein 7 in Chinese liver fluke Clonorchis sinensis

Multidrug resistance-associated protein 7 (MRP7, ABCC10) is a C subfamily member of the ATP-binding cassette (ABC) superfamily. MRP7 is a lipophilic anion transporter that pumps endogenous and xenobiotic substrates from the cytoplasm to the extracellular milieu. Here, we cloned and characterized CsMRP7 as a novel ABC transporter from the Chinese liver fluke, Clonorchis sinensis. Full-length cDNA of CsMRP7 was 5174 nt, encoded 1636 amino acids (aa), and harbored a 147-bp 5'-untranslated region (5'-UTR) and 116-bp 3'-UTR. Phylogenetic analysis confirmed that CsMRP7 was closer to the ABCC subfamily than the ABCB subfamily. Tertiary structures of the N-terminal region (1-322 aa) and core region (323-1621 aa) of CsMRP7 were generated by homology modeling using glucagon receptor (PDB ID: 5ee7_A) and P-glycoprotein (PDB ID: 4f4c_A) as templates, respectively. CsMRP7 nucleotide-binding domain 2 (NBD2) was conserved more than NBD1, which was the sites of ATP binding and hydrolysis. Like typical long MRPs, CsMRP7 has an additional membrane-spanning domain 0 (MSD0) and cytoplasmic loop, along with a common structural fold consisting of MSD1-NBD1-MSD2-NBD2 as a single polypeptide assembly. MSD0, MSD1, and MSD2 consisted of TM1-7, TM8-13, and TM14-19, respectively. The CsMRP7 transcript was more abundant in the metacercariae than in the adult worms. Truncated NBD1 (39 kDa) and NBD2 (44 kDa) were produced in bacteria and mouse immune sera were raised. CsMRP7 was localized in the apical side of the intestinal epithelium, sperm in the testes and seminal receptacle, receptacle membrane, and mesenchymal tissue around intestine in the adult worm. These results provide molecular information and insights into structural and functional characteristics of CsMRP7 and homologs of flukes.

Cloning, expression and enzymatic characterization of 3-phosphoglycerate kinase from Schistosoma japonicum

In the present study, a full-length cDNA encoding the Schistosoma japonicum 3-phosphoglycerate kinase (SjPGK) with an open reading frame of 1251 bp was isolated from 42-day-old (42-d) schistosome cDNAs. Real-time quantitative reverse transcription PCR analysis revealed that SjPGK was expressed in all investigated developmental stages and at a higher transcript levels in 21- and 42-d worms. Moreover, the SjPGK mRNA level was significantly downregulated in 10-d schistosomula from Wistar rats (non-susceptible host). SjPGK was subcloned into pET28a(+) and expressed as both supernatant and inclusion bodies in Escherichia coli BL21 cells. The enzymatic activity of recombinant SjPGK protein (rSjPGK) was 125 U/mg. Kinetic analyses with respect to 3-phosphoglycerate (3-PGA) as substrate gave a Km of 2.69 mmol/L and a Vmax of 748 μmol/min/mg protein. rSjPGK was highly stable over a range of pH 8.0-9.0 and temperature of 30°C-40 °C under physiological conditions. Immunolocalization analysis showed that SjPGK was mainly distributed in the tegument and parenchyma of schistosomes. Western blotting showed that rSjPGK had good immunogenicity. We vaccinated BALB/c mice with rSjPGK combined with Seppic 206 adjuvant. However, there were no significant reductions in the numbers of worms of eggs in the liver, as compared to adjuvant or blank control groups in two independent vaccination tests. This study provides the basis for further investigations into the biological function of SjPGK, although it might not be suitable as a potential vaccine candidate against schistosomiasis.

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.

Advanced enzymology, expression profile and immune response of Clonorchis sinensis hexokinase show its application potential for prevention and control of clonorchiasis

BACKGROUND

Approximately 35 million people are infected with Clonorchis sinensis (C. sinensis) globally, of whom 15 million are in China. Glycolytic enzymes are recognized as crucial molecules for trematode survival and have been targeted for vaccine and drug development. Hexokinase of C. sinensis (CsHK), as the first key regulatory enzyme of the glycolytic pathway, was investigated in the current study.

PRINCIPAL FINDINGS

There were differences in spatial structure and affinities for hexoses and phosphate donors between CsHK and HKs from humans or rats, the definitive hosts of C. sinensis. Effectors (AMP, PEP, and citrate) and a small molecular inhibitor regulated the enzymatic activity of rCsHK, and various allosteric systems were detected. CsHK was distributed in the worm extensively as well as in liver tissue and serum from C. sinensis infected rats. Furthermore, high-level specific IgG1 and IgG2a were induced in rats by immunization with rCsHK. The enzymatic activity of CsHK was suppressed by the antibody in vitro. Additionally, the survival of C. sinensis was inhibited by the antibody in vivo and in vitro.

CONCLUSIONS/SIGNIFICANCE

Due to differences in putative spatial structure and enzymology between CsHK and HK from the host, its extensive distribution in adult worms, and its expression profile as a component of excretory/secretory products, together with its good immunogenicity and immunoreactivity, as a key glycolytic enzyme, CsHK shows potential as a vaccine and as a promising drug target for Clonorchiasis.

Identification and molecular characterization of Parkin in Clonorchis sinensis

Clonorchis sinensis habitating in the bile duct of mammals causes clonorchiasis endemic in East Asian countries. Parkin is a RING-between-RING protein and has E3-ubiquitin ligase activity catalyzing ubiquitination and degradation of substrate proteins. A cDNA clone of C. sinensis was predicted to encode a polypeptide homologous to parkin (CsParkin) including 5 domains (Ubl, RING0, RING1, IBR, and RING2). The cysteine and histidine residues binding to Zn(2+) were all conserved and participated in formation of tertiary structural RINGs. Conserved residues were also an E2-binding site in RING1 domain and a catalytic cysteine residue in the RING2 domain. Native CsParkin was determined to have an estimated molecular weight of 45.7 kDa from C. sinensis adults by immunoblotting. CsParkin revealed E3-ubiquitin ligase activity and higher expression in metacercariae than in adults. CsParkin was localized in the locomotive and male reproductive organs of C. sinensis adults, and extensively in metacercariae. Parkin has been found to participate in regulating mitochondrial function and energy metabolism in mammalian cells. From these results, it is suggested that CsParkin play roles in energy metabolism of the locomotive organs, and possibly in protein metabolism of the reproductive organs of C. sinensis.

Towards improved diagnosis of neglected zoonotic trematodes using a One Health approach

Reaching the goal of control, elimination and eradication of the Neglected Tropical Disease in a foreseeable future provides significant challenges at the ground level especially regarding helminthiasis. Helminths are still mainly diagnoses by egg identification in stool, methods with low sensitivity and for most species low specificity. Cross-sectoral collaboration with regard to zoonoses is almost non-existing and cross-validation by inter-laboratory evaluation of diagnostic tests is not a common practice. The aim of this review was to elucidate the dilemma of helminth diagnosis using zoonotic trematodes as examples. Much progress has been made improving the diagnostic sensitivity of Opisthorchis and Clonorchis using DNA-based techniques but the specificity of these tests is still a challenge due to the many most common but neglected intestinal trematodes. The burden of these diseases and ways to control them remains to be elucidated. Although efficacious drugs are available, the effectiveness of mass drug administration remains to be assessed. The importance of animal reservoirs and ways to control the diseases in animals are yet unknown. Diagnostic challenges regarding Schistosoma japonicum and Schistosoma mekongi include the many light infections and the persisting influx from the animal reservoirs. The sensitivity of the faecal based techniques suited morbidity control but will be insufficient for elimination of the helminths. More accurate diagnostic tools are required and new algorithms for detection and progression of helminth elimination will be needed. Standardized inter-laboratory test validation, inter-sectoral collaboration and establishment of an international One Health diagnostic platform, sharing best practices on diagnosis of helminth zoonoses, could all significantly contribute to control and elimination of these diseases.

Sequence analysis and molecular characterization of Clonorchis sinensis hexokinase, an unusual trimeric 50-kDa glucose-6-phosphate-sensitive allosteric enzyme

Clonorchiasis, which is induced by the infection of Clonorchis sinensis (C. sinensis), is highly associated with cholangiocarcinoma. Because the available examination, treatment and interrupting transmission provide limited opportunities to prevent infection, it is urgent to develop integrated strategies to prevent and control clonorchiasis. Glycolytic enzymes are crucial molecules for trematode survival and have been targeted for drug development. Hexokinase of C. sinensis (CsHK), the first key regulatory enzyme of the glycolytic pathway, was characterized in this study. The calculated molecular mass (Mr) of CsHK was 50.0 kDa. The obtained recombinant CsHK (rCsHK) was a homotrimer with an Mr of approximately 164 kDa, as determined using native PAGE and gel filtration. The highest activity was obtained with 50 mM glycine-NaOH at pH 10 and 100 mM Tris-HCl at pH 8.5 and 10. The kinetics of rCsHK has a moderate thermal stability. Compared to that of the corresponding negative control, the enzymatic activity was significantly inhibited by praziquantel (PZQ) and anti-rCsHK serum. rCsHK was homotropically and allosterically activated by its substrates, including glucose, mannose, fructose, and ATP. ADP exhibited mixed allosteric effect on rCsHK with respect to ATP, while inorganic pyrophosphate (PPi) displayed net allosteric activation with various allosteric systems. Fructose behaved as a dose-dependent V activator with the substrate glucose. Glucose-6-phosphate (G6P) displayed net allosteric inhibition on rCsHK with respect to ATP or glucose with various allosteric systems in a dose-independent manner. There were differences in both mRNA and protein levels of CsHK among the life stages of adult worm, metacercaria, excysted metacercaria and egg of C. sinensis, suggesting different energy requirements during different development stages. Our study furthers the understanding of the biological functions of CsHK and supports the need to screen for small molecule inhibitors of CsHK to interfere with glycolysis in C. sinensis.

Development of a polymerase chain reaction applicable to rapid and sensitive detection of Clonorchis sinensis eggs in human stool samples

Microscopic examination of eggs of parasitic helminths in stool samples has been the most widely used classical diagnostic method for infections, but tiny and low numbers of eggs in stool samples often hamper diagnosis of helminthic infections with classical microscopic examination. Moreover, it is also difficult to differentiate parasite eggs by the classical method, if they have similar morphological characteristics. In this study, we developed a rapid and sensitive polymerase chain reaction (PCR)-based molecular diagnostic method for detection of Clonorchis sinensis eggs in stool samples. Nine primers were designed based on the long-terminal repeat (LTR) of C. sinensis retrotransposon1 (CsRn1) gene, and seven PCR primer sets were paired. Polymerase chain reaction with each primer pair produced specific amplicons for C. sinensis, but not for other trematodes including Metagonimus yokogawai and Paragonimus westermani. Particularly, three primer sets were able to detect 10 C. sinensis eggs and were applicable to amplify specific amplicons from DNA samples purified from stool of C. sinensis-infected patients. This PCR method could be useful for diagnosis of C. sinensis infections in human stool samples with a high level of specificity and sensitivity.

An integrated immunoproteomics and bioinformatics approach for the analysis of Schistosoma japonicum tegument proteins

Schistosomiasis remains one of the major neglected tropical diseases (NTDs) causing morbidity of humans residing in the tropical countries. Much effort has been devoted to the development of vaccines, since it is recognized that vaccines can be served as an important supplementary component alongside chemotherapy for the future control and elimination of schistosomiasis. To accelerate digging new potential target antigens, it is essential to extensively and intensively search immunogenic proteins in a high-throughput manner using proteomics-microarray techniques. In the present study, an integrated immunoproteomics and bioinformatics approach was used to profile the tegument of the human blood fluke Schistosoma japonicum. Results showed that the full-length tegument proteins were high-throughput cloned and expressed and screened with sera from S. japonicum-infected patients and normal subjects using protein arrays. Here, thirty highly immunoreactive tegument proteins and 10 antigens with an AUC value greater than 0.90 were identified at first time. In particularly, STIP1, the highest immunoreactive tegument protein has been shown good antigenicity and immunogenicity, and thus makes it to be a potential target for designing anti-parasite drug or vaccine.

BIOLOGICAL SIGNIFICANCE

The schistosome tegument plays a crucial role in host-parasite interactions and there are several tegument proteins that proved to be potential vaccine candidates. However, vaccines are not yet available, thus it is important to identify new target antigens from schistosome tegument proteome. Herein, we demonstrate that the S. japonicum tegument proteins were analyzed by an integrated immunoproteomics and bioinformatics approach. We found that thirty highly immunoreactive tegument proteins and 10 antigens with an AUC value greater than 0.90 were identified for the first time. In particularly, we found 17 of tegument immunoproteomes having putative interaction networks with other proteins of S. japonicum. The results will provide clues of potential target molecules for vaccine development and biomarkers for diagnostics of schistosomiasis.

Molecular characterization of voltage-gated calcium channel β-subunits of Clonorchis sinensis

The voltage-gated Ca(2+) channel β-subunit is a member of the membrane-associated guanylate kinase family and modulates kinetic properties of the Ca(2+) channels, such as their voltage-dependent activation and inactivation rates. Two cDNA clones were identified to encode each β-subunit isotype of the voltage-gated Ca(2+) channel of Clonorchis sinensis, CsCavβ1 and CsCavβ2, which consist of 606 and 887 amino acids, respectively. CsCavβ1 was found to be similar to the β-subunit containing two conserved serine residues that constitute the consensus protein kinase C phosphorylation site in the β-interaction domain (BID). CsCavβ2 had cysteine and alanine residues instead of the two serine residues conserved in BID and was homologous to variant β-subunit of Schistosoma mansoni and Schistosoma japonicum. CsCavβ1 and CsCavβ2 were almost equally expressed in the adults and metacercariae, but were more expressed in adult C. sinensis than in metacercariae. Collectively, our findings suggest that substitution of the two serine residues in BID of CsCavβ2 may render C. sinensis sensitive to praziquantel.

Ascaris suum enolase is a potential vaccine candidate against ascariasis

Ascariasis caused by Ascaris is the most common parasite problem in humans and pigs worldwide. No vaccines are available for the prevention of Ascaris infections. In the present study, the gene encoding Ascaris suum enolase (As-enol-1) was amplified, cloned and sequenced. Amino acid sequence alignment indicated that As-enol-1 was highly conserved between different nematodes and shared the highest identity (87%) with enolase from Anisakis simplex s.l. The recombinant pVAX-Enol was successfully expressed in Marc-145 cells. The ability of the pVAX-Enol for inducing immune protective responses against challenge infection with A. suum L3 was evaluated in Kunming mice. The immune response was evaluated by lymphoproliferative assay, cytokine and antibody measurements, and the reduction rate of recovery larvae. The results showed that the mice immunized with pVAX-Enol developed a high level of specific antibody responses against A. suum, a strong lymphoproliferative response, and significant levels of IFN-γ, IL-2, IL-4 and IL-10 production, compared with the other groups immunized with empty plasmid or blank controls, respectively. There was a 61.13% reduction (P<0.05) in larvae recovery compared with that in the blank control group. Our data indicated that A. suum enolase is a potential vaccine candidate against A. suum infection.

Tracing of the Bile-chemotactic migration of juvenile Clonorchis sinensis in rabbits by PET-CT

Background

Adult Clonorchis sinensis live in the bile duct and cause clonorchiasis. It is known that the C. sinensis metacercariae excyst in the duodenum and migrate up to the bile duct through the common bile duct. However, no direct evidence is available on the in vivo migration of newly excysted C. sinensis juveniles (CsNEJs). Advanced imaging technologies now allow the in vivo migration and localization to be visualized. In the present study, we sought to determine how sensitively CsNEJs respond to bile and how fast they migrate to the intrahepatic bile duct using PET-CT.

Methodology/Principal Findings

CsNEJs were radiolabeled with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). Rabbits with a gallbladder contraction response to cholecystokinin-8 (CCK-8) injection were pre-screened using cholescintigraphy. In these rabbits, gallbladders contracted by 50% in volume at an average of 11.5 min post-injection. The four rabbits examined were kept anesthetized and a catheter inserted into the mid duodenum. Gallbladder contraction was stimulated by injecting CCK-8 (20 ng/kg every minute) over the experiment. Anatomical images were acquired by CT initially and dynamic PET was then carried out for 90 min with a 3-min acquisition per frame. Twelve minutes after CCK-8 injection, about 3,000 ¹⁸F-FDG-labeled CsNEJs were inoculated into the mid duodenum through the catheter. Photon signals were detected in the liver 7–9 min after CsNEJs inoculation, and these then increased in the whole liver with stronger intensity in the central area, presenting that the CsNEJs were arriving at the intrahepatic bile ducts.

Conclusion

In the duodenum, CsNEJs immediately sense bile and migrate quickly with bile-chemotaxis to reach the intrahepatic bile ducts by way of the ampulla of Vater.

Clonorchis sinensis adults habituating in the bile duct cause clonorchiasis endemic in East Asian countries, in which about 15–20 million people are supposedly infected. It has previously been reported that C. sinensis metacercariae excyst in the duodenum and that the juvenile flukes migrate to the bile duct through the ampulla of Vater in 4–7 hours. Recently advanced imaging technologies have enabled visualization of movements and localizations of parasites in mammalian hosts. From present study, we found the following: newly excysted C. sinensis juveniles (CsNEJs) were efficiently in vitro radiolabeled with ¹⁸F-FDG since CsNEJs have glucose transporters; CCK-8-induced gallbladder contraction was various rabbit to rabbit; CsNEJs promptly recognized bile and migrated up the duodenum to reach the intrahepatic bile ducts by way of the ampulla of Vater and the common bile duct as early as 7–9 minutes after inoculation. Some CsNEJs responding slowly to the bile delayed arriving at the distal bile capillaries. It was visualized for the first time that the CsNEJs migrate quickly within 10–20 minutes from the duodenum to the intrahepatic bile duct. These findings provide fundamental information on the migration of parasites living in the biliary passages of mammals.

The draft genome of the carcinogenic human liver fluke Clonorchis sinensis

Background

Clonorchis sinensis is a carcinogenic human liver fluke that is widespread in Asian countries. Increasing infection rates of this neglected tropical disease are leading to negative economic and public health consequences in affected regions. Experimental and epidemiological studies have shown a strong association between the incidence of cholangiocarcinoma and the infection rate of C. sinensis. To aid research into this organism, we have sequenced its genome.

Results

We combined de novo sequencing with computational techniques to provide new information about the biology of this liver fluke. The assembled genome has a total size of 516 Mb with a scaffold N50 length of 42 kb. Approximately 16,000 reliable protein-coding gene models were predicted. Genes for the complete pathways for glycolysis, the Krebs cycle and fatty acid metabolism were found, but key genes involved in fatty acid biosynthesis are missing from the genome, reflecting the parasitic lifestyle of a liver fluke that receives lipids from the bile of its host. We also identified pathogenic molecules that may contribute to liver fluke-induced hepatobiliary diseases. Large proteins such as multifunctional secreted proteases and tegumental proteins were identified as potential targets for the development of drugs and vaccines.

Conclusions

This study provides valuable genomic information about the human liver fluke C. sinensis and adds to our knowledge on the biology of the parasite. The draft genome will serve as a platform to develop new strategies for parasite control.

Seasonal features of Heterophyopsis continua metacercariae in perches, Lateolabrax japonicus, and infectivity to the final host

As the second intermediate host, the perch Lateolabrax japonicus provides metacercariae of Heterophyopsis continua to man. Fry of the perch arrive at and grow to mid-sized fish in the brackish water of Jinju Bay, South Korea. The H. continua metacercariae occur in perch as small and mid-sized forms in July and grow to the large form by August. The size distribution of metacercariae shifts dominantly to the large form in September and then remains as it was. Adult H. continua recovery was high from experimental chicks infected with the medium and large metacercariae collected in September and reduced to half from the chicks infected with those of October. Collectively, the H. continua metacercariae grew to the large form in about 20 days and achieved infectivity to chicks after 2 months in the perches.

Functional genes and proteins of Clonorchis sinensis

During the past several decades, researches on parasite genetics have progressed from biochemical and serodiagnostic studies to protein chemistry, molecular biology, and functional gene studies. Nowadays, bioinformatics, genomics, and proteomics approaches are being applied by Korean parasitology researchers. As for Clonorchis sinensis, investigations have been carried out to identify its functional genes using forward and reverse genetic approaches and to characterize the biochemical and biological properties of its gene products. The authors review the proteins of cloned genes, which include antigenic proteins, physiologic and metabolic enzymes, and the gene expression profile of Clonorchis sinensis.

Molecular characterization of a novel Clonorchis sinensis secretory phospholipase A(2) and investigation of its potential contribution to hepatic fibrosis

A gene encoding a homologue of phospholipase A(2) was identified from the Clonorchis sinensis adult cDNA plasmid library. The deduced amino acid sequence including a signal peptide that has 28-46% identity with secretory phospholipase A(2), group III (group III sPLA(2)) of other species. It also has typical features of group III sPLA(2)s including 10 cysteines, the key residues of the Ca(2+) loop and catalytic site. The recombinant protein encoded by this gene expressed in Escherichia coli showed a product of about 34kDa in SDS-PAGE. Prediction of signal peptide and Western blot analysis indicated the group III secretory phospholipase A(2) of C. sinensis (CsGIIIsPLA(2)) was an excretory-secretory product (ES product). The enzyme activity of the recombinant protein was determined using phosphatidylcholine as substrates. The result revealed that the protein was a Ca(2+)-dependent PLA(2). Both MTT test and cell cycle analysis of LX-2 showed a higher percentage of cells are in proliferation phase. Semi-quantitative RT-PCR experiments demonstrated an up-regulated expression of collagen III in these cells after incubation with the recombinant protein. We also identified that the recombinant CsGIIIsPLA(2) could bind to some membrane proteins on LX-2 cells specifically by immunofluorescence, thus there might be receptors of CsGIIIsPLA(2) on the LX-2 cell membrane. Our results suggest that CsGIIIsPLA(2) might play an important role in the initiation and development of hepatic fibrosis caused by C. sinensis.

Reference genes for quantitative analysis on Clonorchis sinensis gene expression by real-time PCR

The accuracies of relative gene expressions as determined by quantitative real-time polymerase chain reaction are largely dependent on the variabilities of the reference genes used. Validation of the stabilities of reference genes under experimental conditions is an essential initial step for comparative studies on the expression levels of target genes in experimental groups. Using three total RNA samples extracted independently from Clonorchis sinensis metacercariae and adults, we determined the gene expression stabilities of eight reference gene candidates and the relative transcript levels of three target genes using the geNorm program. The reference genes found to be stably expressed in metacercariae and adults were phosphoglycerate kinase, beta-actin, and calcyphosine; reference genes found to be stably expressed under gamma-irradiated and non-irradiated conditions were succinate dehydrogenase, small nuclear ribonucleoprotein, and beta-actin; and those stably expressed regardless of bile treatment were small nuclear ribonucleoprotein, phosphoglycerate kinase, and succinate dehydrogenase. According to our data, the expression levels of target genes are dependent on normalization factors, such as the C (T) values of single reference genes and the geometric mean of the C (T) values of three reference genes. When comparing C. sinensis gene expressions, we propose to employ the geometric mean of the C (T) values of more than three reference genes validated in the same experimental setting.

Cloning and expression of mitochondrial malate dehydrogenase of Clonorchis sinensis

The NAD-dependent mitochondrial malate dehydrogenase (mMDH, EC1.1.1.37) plays pivotal roles in tricarboxylic acid and is crucial for the survival and pathogenecity of parasites. A cDNA, which was identified by high throughput sequencing from the cDNA library constructed from adult Clonorchis sinensis, encoded a putative peptide of 341 amino acids with more than 50% identity with mMDHs from other organisms. The mMDH was expressed in Escherichia coli as the recombinant protein with a GST tag and purified by glutathione-Sepharose 4B column. The recombinant mMDH showed MDH activity of 63.6 U/mg, without lactate dehydrogenase activity and NADPH selectivity. The kinetic constants of recombinant mMDH were determined.

Gene expression of Clonorchis sinensis metacercaria induced by gamma irradiation

Gamma-rays are a form of ionizing radiation and produce serious cellular damage to nuclei and organelles. Gamma irradiation induces the expressions of genes involved in DNA repair. Clonorchis sinensis resides in and provokes pathophysiologic changes in the bile ducts of mammals. The C. sinensis metacercariae are unsusceptible or resistant to gamma irradiation with LD50 of 16.5 Gy. Using the annealing control primer-based polymerase chain reaction (PCR) method, 19 genes were found to be up-regulated in C. sinensis metacercariae exposed to gamma rays. Contigs of up-regulated genes (URGs) were retrieved in a C. sinensis expressed sequence tag pool and extended by DNA-walking. Of the 13 URGs annotated putatively as functional genes, five URGs were associated with energy metabolism, six with protein processing, and the other two with DNA repair protein RAD23 and inhibitor of apoptosis protein. Four URGs were confirmed up-regulated by gamma irradiation by quantitative real-time PCR. One unknown gene, which was up-regulated to the greatest extent, might contribute to early recovery from gamma-irradiation-induced damage. The up-regulations of genes encoding DNA repair, protein processing, and energy metabolism proteins suggests that increases in gene products orchestrate DNA lesion repair and recover cellular functions in gamma-irradiated C. sinensis metacercariae.

Molecular cloning and characterization of WD40-repeat protein from Clonorchis sinensis

WD40-repeat proteins have four to eight repeating units flanked by Gly-His (GH) and Trp-Asp (WD) at both termini and folds into a beta-propeller. A polypeptide deduced from a Clonorchis sinensis cDNA clone analyzed to have seven WD40-repeats and predicted to form a beta-propeller (CsWD1). The CsWD1 protein was expressed stage-specifically in the metacercariae and localized in the tegumental syncytium. The CsWD1 protein is suggested to serve as a platform for interacting partner proteins in the tegumental syncytium of C. sinensis metacercariae.

Molecular cloning and phylogenetic analysis of Clonorchis sinensis elongation factor-1α

Elongation factor-1 (EF-1) plays a primary role in protein synthesis, e.g., in the regulation of cell growth, aging, motility, embryogenesis, and signal transduction. The authors identified a clone CsIH23 by immunoscreening a Clonorchis sinensis cDNA library. The cDNA of CsIH23 was found to have a putative open reading frame containing 461 amino acids with a predicted molecular mass of 50.5 kDa. Its polypeptide sequence was highly homologous with EF-1alpha of parasites and vertebrate animals. CsIH23 polypeptide contained three GTP/GDP-binding sites, one ribosome-binding domain, one actin-binding domain, one tRNA-binding domain, and two glyceryl-phosphoryl-ethanolamine attachment sites. Based on these primary and secondary structural similarities, it was concluded that CsIH23 cDNA encodes C. sinensis EF-1alpha (CsEF-1alpha). In a molecular phylogenic tree, CsEF-1alpha clustered with the EF-1alpha of helminthic parasites. Subsequently, CsEF-1alpha recombinant protein was bacterially overexpressed and purified by Ni-NTA affinity column chromatography. Immunoblotting using CsEF-1alpha recombinant protein produced positive signals for all serum samples tested from clonorchiasis, opisthorchiasis viverinii, and paragonimiasis westermani patients and normal healthy controls. These findings suggest that recombinant CsEF-1alpha is of limited usefulness as serodiagnostic antigen for clonorchiasis.

Partner proteins that interact with Clonorchis sinensis WD40-repeat protein

WD40-repeat proteins have four to eight repeat units, which have Gly-His (GH) and Trp-Asp (WD) at both termini and fold into a beta-propeller. In particular, the WD40-repeat protein of Clonorchis sinensis (CsWD1) has seven WD-repeat units and is expressed stage-specifically in metacercariae. By yeast two-hybrid screening, putative interacting protein cDNAs were cloned from a C. sinensis metacercaria cDNA library and purified further by higher stringency screening and lacZ colony-lift assay. After assessing their nucleotide and polypeptide sequences, 21 putative partner protein cDNAs were selected and assembled into 14 clones. Using YRG2 strain yeast, 12 putative partner protein clones were confirmed to interact with CsWD1 protein. These 12 proteins were grouped into functional categories, i.e., signal proteins, transporters, proteases, and muscle proteins. These results suggest that CsWD1 protein is associated with intracellular protein translocation and cell cycle control in C. sinensis metacercaria.

Expressed sequence tag analysis of adult Clonorchis sinensis, the Chinese liver fluke

Expressed sequence tag (EST) pools represent partial profiles of the gene expressions of organisms. In an effort to construct a Clonorchis sinensis EST pool, 2,387 ESTs were collected from an adult C. sinensis cDNA library and assembled into 1,573 clusters. Of these clusters, 1,225 ESTs (51%) were singletons and 348 clusters consisted of more than two ESTs. There were 848 clusters (54%) that shared significant identity with previously reported proteins, and of these, 401 clusters were categorized into 11 major functional protein classes. Three cDNA clones of fructose-1,6-bisphosphate (FBP) aldolase were selected from the C. sinensis EST pool and analyzed for phylogenic clustering. FBP clones encoded a complete polypeptide, which shared significant identity to those of vertebrate and invertebrate animals and clustered with those of trematodes. We believe that the EST pool described can be confidently used as a platform in multigene researches on C. sinensis gene expression.

Enzymatic and physico-chemical characteristics of recombinant cMDH and mMDH of Clonorchis sinensis

The cytosol and mitochondrial malate dehydrogenases (MDHs, EC 1.1.1.37) of Clonorchis sinensis were expressed in Escherichia coli as a fusion protein with a 6xHis and GST tag, respectively. The cytosol MDH of Clonorchis sinensis (Cs-cMDH) has higher resistibility to acid than mitochondrial MDH (Cs-mMDH). The Cs-cMDH also has higher heat resistibility and thermal stability than Cs-mMDH. Although there is only 22.8% identity between the amino acid sequences of Cs-cMDH and Cs-mMDH, they share several conserved residues. There are some differences between the circular dichroism spectra of Cs-cMDH and Cs-mMDH, but they have approximate percentages of helix. 4,4'-Bisdimethylamino diphenylcarbinol can decrease the Cs-mMDH activity but not the Cs-cMDH activity. Paraziquantel, metronidazole and albendazole did not inhibit the enzymes' activity, but adenosine 5'-monophosphate showed competitive inhibition to enzyme, with the Ki for Cs-cMDH and Cs-mMDH being 2.81 and 0.49 mM, respectively.

Rational strain improvement for enhanced clavulanic acid production by genetic engineering of the glycolytic pathway in Streptomyces clavuligerus

Clavulanic acid is a potent beta-lactamase inhibitor used to combat resistance to penicillin and cephalosporin antibiotics. There is a demand for high-yielding fermentation strains for industrial production of this valuable product. Clavulanic acid biosynthesis is initiated by the condensation of L-arginine and D-glyceraldehyde-3-phosphate (G3P). To overcome the limited G3P pool and improve clavulanic acid production, we genetically engineered the glycolytic pathway in Streptomyces clavuligerus. Two genes (gap1 and gap2) whose protein products are distinct glyceraldehyde-3-phosphate dehydrogenases (GAPDHs) were inactivated in S. clavuligerus by targeted gene disruption. A doubled production of clavulanic acid was consistently obtained when gap1 was disrupted, and reversed by complementation. Addition of arginine to the cultured mutant further improved clavulanic acid production giving a greater than 2-fold increase over wild type, suggesting that arginine became limiting for biosynthesis. This is the first reported application of genetic engineering to channel precursor flux to improve clavulanic acid production.