Cloning and expression of a cysteine proteinase gene from Paragonimus westermani adult worms

Roles of Cysteine Proteases in Biology and Pathogenesis of Parasites

Cysteine proteases, also known as thiol proteases, are a class of nucleophilic proteolytic enzymes containing cysteine residues in the enzymatic domain. These proteases generally play a pivotal role in many biological reactions, such as catabolic functions and protein processing, in all living organisms. They specifically take part in many important biological processes, especially in the absorption of nutrients, invasion, virulence, and immune evasion of parasitic organisms from unicellular protozoa to multicellular helminths. They can also be used as parasite diagnostic antigens and targets for gene modification and chemotherapy, as well as vaccine candidates, due to their species and even life-cycle stage specificity. This article highlights current knowledge on parasitic cysteine protease types, biological functions, and their applications in immunodiagnosis and chemotherapy.

Characterization and localization of antigens for serodiagnosis of human paragonimiasis

Paragonimiasis is a foodborne trematode infection that affects 23 million people, mainly in Asia. Lung fluke infections lead frequently to chronic cough with fever and hemoptysis, and are often confused with lung cancer or tuberculosis. Paragonimiasis can be efficiently treated with praziquantel, but diagnosis is often delayed, and patients are frequently treated for other conditions. To improve diagnosis, we selected five Paragonimus kellicotti proteins based on transcriptional abundance, recognition by patient sera, and conservation among trematodes and expressed them as His-fusion proteins in Escherichia coli. Sequences for these proteins have 76-99% identity with amino acid sequences for orthologs in the genomes of Paragonimus westermani, Paragonimus heterotremus, and Paragonimus miyazakii. Immunohistology studies showed that antibodies raised to four recombinant proteins bound to the tegument of adult P. kellicotti worms, at the parasite host interface. Only a known egg antigen was absent from the tegument but present in developing and mature eggs. We evaluated the diagnostic potential of these antigens by Western blot with sera from patients with paragonimiasis (from MO and the Philippines), fascioliasis, and schistosomiasis, and with sera from healthy North American controls. Two recombinant proteins (a cysteine protease and a myoglobin) showed the highest sensitivity and specificity as diagnostic antigens, and they detected antibodies in sera from paragonimiasis patients with early or mature infections. In contrast, antibodies to egg yolk ferritin appeared to be specific marker for patients with adult fluke infections that produce eggs. Our study has identified and localized antigens that are promising for serodiagnosis of human paragonimiasis.

Characterization of Spirometra erinaceieuropaei Plerocercoid Cysteine Protease and Potential Application for Serodiagnosis of Sparganosis

Background

Sparganosis is a neglected but important food-borne parasitic zoonosis. Clinical diagnosis of sparganosis is difficult because there are no specific manifestations. ELISA using plerocercoid crude or excretory–secretory (ES) antigens has high sensitivity but has cross-reactions with other helminthiases. The aim of this study was to characterize Spirometra erinaceieuropaei cysteine protease (SeCP) and to evaluate its potential application for serodiagnosis of sparganosis.

Methodology/Principal Findings

The full length SeCP gene was cloned, and recombinant SeCP (rSeCP) was expressed and purified. Western blotting showed that rSeCP was recognized by the serum of sparganum-infected mice, and anti-rSeCP serum recognized the native SeCP protein of plerocercoid crude or ES antigens. Expression of SeCP was observed at plerocercoid stages but not at the adult and egg stages. Immunolocalization identified SeCP in plerocercoid tegument and parenchymal tissue. The rSeCP had CP activity, and the optimum pH and temperature were 5.5 and 37°C, respectively. Enzymatic activity was significantly inhibited by E-64. rSeCP functions to degrade different proteins and the function was inhibited by anti-rSeCP serum and E-64. Immunization of mice with rSeCP induced Th2-predominant immune responses and anti-rSeCP antibodies had the potential capabilities to kill plerocercoids in an ADCC assay. The sensitivity of rSeCP-ELISA and ES antigen ELISA was 100% when performed on sera of patients with sparganosis. The specificity of rSeCP-ELISA and ES antigen ELISA was 98.22% (166/169) and 87.57% (148/169), respectively (P<0.05).

Conclusions

The rSeCP had the CP enzymatic activity and SeCP seems to be important for the survival of plerocercoids in host. The rSeCP is a potential diagnostic antigen for sparganosis.

Sparganosis is a neglected tropical disease; its diagnosis is difficult and it is often misdiagnosed. ELISA using the crude or ES antigens of plerocercoids cross reacts with other helminthiases. Cysteine protease is a type of hydrolase and plays important roles in the development and survival of parasites; it has been used for diagnostic markers and vaccine targets for some parasitic diseases. In this study, a 36 kDa Spirometra erinaceieuropaei cysteine protease (SeCP) was expressed and purified. The results showed that SeCP was a plerocercoid stage-specific protein located in the teguments and parenchymal tissue. The rSeCP had cysteine protease activity and functioned to degrade host proteins. Vaccination of mice with rSeCP induced high levels of IgG1 and anti-rSeCP antibodies with the ability to kill plerocercoids in an ADCC assay. The rSeCP had a high sensitivity and specificity for detecting anti-plerocercoid antibodies, and could be used as a potential antigen for serodiagnosis of sparganosis.

Identification of immunodominant excretory–secretory cysteine proteases of adultParagonimus westermani by proteome analysis

Paragonimus westermani causes inflammatory lung disease in humans. The parasite excretes a host of biologically active molecules, which are thought to be involved in pathophysiological and immunological events during infection. Analyses of the 2-DE protein profiles of the excretory-secretory products (ESP) of adult P. westermani revealed approximately 147 protein spots, at least 15 of which were identified as cysteine proteases (CPs), at pHs between 4.5 and 8.5, and molecular weights (MWs) between 27 and 35 kDa. An additional three CPs (designated as PwCP-3, -8 and -11) were newly recognized by TOF/TOF MS. Their molecular biological information, which shared a high level sequence homology, was elucidated. The majority of the CPs reacted strongly with sera from paragonimiasis patients. When we observed the chronological changes in the antibody responses of the respective CPs against canine sera collected serially at 1, 3, 5, 7, 11 and 14 wk after experimental infection, these molecules exhibited a multiplicity of distinct immune recognition patterns. Our results clearly showed that P. westermani adult ESP were principally composed of excretory-secretory CPs, and that these CPs may exert effects not only on host tissue degradation and nutrient uptake, but also on the immune-regulating cells via synergistic and independent interactions.

Expression of cysteine proteinase of Clonorchis sinensis and its use in serodiagnosis of clonorchiasis

A gene encoding cysteine proteinase from Clonorchis sinensis has been cloned and expressed in Escherichia coli. The cysteine proteinase cDNA fragment was amplified by reverse transcription-polymerase chain reaction using degenerate oligonucleotide primers derived from conserved active site of cysteine proteinases. The 5' and 3' regions of the gene were amplified using rapid amplification of cDNA ends. The cloned gene has an open reading frame of 696 bp and deduced amino acid sequence of 232. Sequence analysis and alignment showed significant homologies with the eukaryotic cysteine proteinases and conservation of the Cys, His, and Asp residues that form the catalytic triad. Analysis of the expressed protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the molecular weight of the protein was approximately 28.5 kDa. Proteolytic activity of the expressed protein was inhibited by cysteine proteinase inhibitors such as L-trans-epoxysuccinyl-leucylamide-(4-guanidino)-butane, iodoacetic acid, and leupeptin. The expressed protein showed biochemical properties similar to those of cysteine proteinases of other parasites. The expressed protein strongly reacted with the sera from patients with clonorchiasis but not with the sera from patients with paragonimiasis, fascioliasis, cysticercosis, and sparganosis, or with sera from normal human controls. These results suggest that the expressed protein may be valuable as a specific diagnostic material for the immunodiagnosis of clonorchiasis.

Cystatin capture enzyme-linked immunosorbent assay for serodiagnosis of human clonorchiasis and profile of captured antigenic protein of Clonorchis sinensis

Enzyme-linked immunosorbent assay (ELISA) with crude extracts of adult Clonorchis sinensis has been reported to have a high degree of sensitivity with a moderate degree of specificity for the serodiagnosis of clonorchiasis. The cystatin capture ELISA was investigated for its usefulness for the serodiagnosis of human clonorchiasis. Cystatin bound specifically to cysteine proteinases in crude extracts of adult C. sinensis worms, and its binding capacity was not hindered competitively by the other proteinase inhibitors tested. The cystatin capture ELISA for clonorchiasis showed a higher degree of specificity than the conventional ELISA, which produced some cross-reactivities to sera from patients with cysticercosis, sparganosis, and opisthorchiasis. Immunoglobulin G antibodies to C. sinensis cysteine proteinases were produced in experimental rabbits at week 3, and their levels increased rapidly and remained at a plateau after 8 weeks of infection. Of the proteins from the C. sinensis crude extract captured with cystatin, seven proteins were reactive with the serum from patients with clonorchiasis. The cystatin capture ELISA is indicated to be a sensitive and highly specific immunodiagnostic assay for serodiagnosis of human clonorchiasis.

Structural and immunological characteristics of a 28-kilodalton cruzipain-like cysteine protease of Paragonimus westermani expressed in the definitive host stage

A complete cDNA sequence encoding a 28-kDa cruzipain-like cysteine protease of adult Paragonimus westermani, termed Pw28CCP, was isolated from an adult cDNA library. The cDNA contained a single open reading frame of 975 bp encoding 325 amino acids, which exhibited the structural motif and domain organization characteristic of cysteine proteases of non-cathepsin Bs including a hydrophobic signal sequence, an ERFNIN motif, and essential cysteine residues as well as active sites in the mature catalytic region. Analysis of its phylogenetic position revealed that this novel enzyme belonged to the cruzipain-like cysteine proteases. The sequence of the first 13 amino acids predicted from the mature domain of Pw28CCP was in accord with that determined from the native 28-kDa enzyme purified from the adult worm. Expression of Pw28CCP was observed specifically in juvenile and adult worms, with a location in the intestinal epithelium, suggesting that this enzyme could be secreted and involved in nutrient uptake and immune modulation. The recombinant protein expressed in Escherichia coli was used to assess antigenicity by immunoblotting with sera from patients with active paragonimiasis and from those with other parasitic infections. The resulting sensitivity of 86.2% (56 of 65 samples) and specificity of 98% (147 of 150 samples) suggest its potential as an antigen for use in immunodiagnosis.