Identification of a protein disulfide isomerase of Neospora caninum in excretory-secretory products and its IgA binding and enzymatic activities

Identification of specific antigens between Toxoplasma gondii and Neospora caninum and application of potential diagnostic antigen TgGRA54

Toxoplasma gondii is a zoonotic parasite that is very common in livestock. Meat products from livestock infected with T. gondii are one of the important transmission routes of toxoplasmosis. Rapid and reliable diagnosis is a prerequisite for the prevention and control of toxoplasmosis. Neospora caninum and T. gondii are similar in morphology and life history, and there are a large number of cross antigens between them, making clinical diagnosis of toxoplasmosis more difficult. In this study, immunoprecipitation-mass spectrometry (IP-MS) was used to screen for T. gondii-specific antigens, and the specific antigen was cloned and expressed in Escherichia coli. The specific antigen was then used to establish an indirect ELISA diagnostic method. A total of 241 specific antigens of T. gondii and 662 cross antigens between T. gondii and N. caninum were screened by IP-MS. Through bioinformatics analysis and homology comparison, seven proteins were selected for gene cloning and prokaryotic expression, and the most suitable antigen, TgGRA54, was selected to establish an indirect ELISA for T. gondii. Compared with the indirect immunofluorescent antibody test (IFAT), the positive coincidence rate of the ELISA based on rTgGRA54 was 100% (72/72) and the negative coincidence rate was 80.95% (17/21). The indirect ELISA method based on TgGRA54 recombinant protein was established to detect T. gondii antibodies in bovine sera, and the recombinant protein reacted well with T. gondii positive sera from sheep, mouse, and swine, indicating that the recombinant protein is a good diagnostic antigen for T. gondii.

The potential role of protein disulfide isomerases (PDIs) during parasitic infections: a focus on Leishmania spp

Leishmaniasis is a group of vector-borne diseases caused by intracellular protozoan parasites belonging to the genus Leishmania. Leishmania parasites can employ different and numerous sophisticated strategies, including modulating host proteins, cell signaling, and cell responses by parasite proteins, to change the infected host conditions to favor the parasite persistence and induce pathogenesis. In this sense, protein disulfide isomerases (PDIs) have been described as crucial proteins that can be modulated during leishmaniasis and affect the pathogenesis process. The effect of modulated PDIs can be investigated in both aspects, parasite PDIs and infected host cell PDIs, during infection. The information concerning PDIs is not sufficient in parasitology; however, this study aimed to provide data regarding the biological functions of such crucial proteins in parasites with a focus on Leishmania spp. and their relevant effects on the pathogenesis process. Although there are no clinical trial vaccines and therapeutic approaches, highlighting this information might be fruitful for the development of novel strategies based on PDIs for the management of parasitic diseases, especially leishmaniasis.

A computer-aided approach to identify novel Leishmania major protein disulfide isomerase inhibitors for treatment of leishmaniasis

Leishmaniasis is an infectious disease caused by parasites of the genus Leishmania and transmitted by the bite of a sand fly. To date, most available drugs for treatment are toxic and beyond the economic means of those affected by the disease. Protein disulfide isomerase (PDI) is a chaperone protein that plays a major role in the folding of newly synthesized proteins, specifically assisting in disulfide bond formation, breakage, or rearrangement in all non-native proteins. In previous work, we demonstrated that Leishmania major PDI (LmPDI) has an essential role in pathogen virulence. Furthermore, inhibition of LmPDI further blocked parasite infection in macrophages. In this study, we utilized a computer-aided approach to design a series of LmPDI inhibitors. Fragment-based virtual screening allowed for the understanding of the inhibitors' modes of action on LmPDI active sites. The generated compounds obtained after multiple rounds of virtual screening were synthesized and significantly inhibited target LmPDI reductase activity and were shown to decrease in vitro parasite growth in human monocyte-derived macrophages. This novel cheminformatics and synthetic approach led to the identification of a new series of compounds that might be optimized into novel drugs, likely more specific and less toxic for the treatment of leishmaniasis.

Immunoproteomic analysis of Schistosoma japonicum schistosomulum proteins recognized by immunoglobulin G in the sera of susceptible and non-susceptible hosts

The aim of this study was to search for immunogenic schistosomula proteins in the hope of identifying novel intervention targets. Schistosomula proteins were analyzed by immunoproteomic which the probes were sera derived from BALB/c mice (susceptible hosts) and Microtus fortis (resistant hosts). A total of 116 immunoreactive proteins recognized by 10 days post-infected BALB/c mice, M. fortis sera, and uninfected M. fortis sera were selected for further analysis. Finally, 95 protein spots were identified by mass spectrometry (MS) analysis. Bioinformatics analysis showed that the differentially identified immunogenic proteins participated mainly in cytoskeleton organization, cell motility, energy metabolism, responses to stimuli, and protein folding. Many of these proteins were the tegument or excretory-secretory products of schistosomes reported in previous studies. Among of them, Schistosoma japonicum DnaJ (Hsp40) homologue (SjDnaJ) was successfully expressed and the purified recombinant product was evaluated by immunoprotective experiment. After immunization of BALB/c mice with recombinant SjDnaJ, it could induce 34.5% and 48.9% reductions in the numbers of worms and eggs in the liver. These results contribute to a better understanding of the molecular mechanisms underlying the host-parasite relationship and provide a major dataset to facilitate the further development of new vaccine candidates and/or diagnostic markers for schistosomiasis.

BIOLOGICAL SIGNIFICANCE

Schistosomiasis is caused by parasitic blood-dwelling flukes in tropical and subtropical areas, and it is one of the world's most prevalent tropical diseases. The lack of effective vaccine and reliable diagnostic methods make this disease difficult to control. In China, S. japonicum can infect more than 40 different susceptible mammals for this parasite. However, M. fortis is the only known mammal where the schistosome cannot develop and it exhibits no significant pathological effects. Many studies' results showed that native antibodies against S. japonicum are present in M. fortis that may have important anti-schistosomiasis roles during the infection process. The aim of this study was to search for immunogenic schistosomula proteins in the hope of identifying novel intervention targets. We present a comparative immunoproteomics analysis of the proteins recognized by susceptible and resistant host antibodies before and 10-days after infections. The results of this analysis will be helpful for identifying the key molecules required for the survival and development of schistosomes. At the same time, the study contributes to a better understanding of the molecular mechanisms underlying the host-parasite relationship associated with schistosomes and they also provide a major dataset to facilitate the further development of new diagnostic assays and/or vaccine candidates for schistosomiasis.

Cloning, expression and characterization of protein disulfide isomerase of Schistosoma japonicum

The excretory/secretory (ES) proteins of schistosomes play important roles in modulating host immune systems and are regarded as potential vaccine candidates and drug targets. Protein disulfide isomerase (PDI) is an essential enzyme that is involved in disulfide bond formation and rearrangement. In the present study, SjPDI, a 52.8 kDa protein previously identified in a proteomics analysis as one of the ES proteins of Schistosoma japonicum, was cloned and characterized. Western blot analysis showed that recombinant SjPDI (rSjPDI) was recognized by serum from rabbits vaccinated with schistosome worm antigen. Worm protein extracts and ES protein extracts from S. japonicum could react with anti-rSjPDI mouse serum. Real-time PCR analysis indicated that SjPDI was expressed at all developmental stages tested, and a high expression level was detected in 42-day-old male worms. Immunofluorescence analysis revealed that SjPDI was mainly distributed on the tegument and parenchyma of S. japonicum worms. An enzyme-linked immunosorbent assay (ELISA) demonstrated that rSjPDI could induce a high level of rSjPDI-specific IgG antibodies. The biological activity of purified rSjPDI was confirmed by isomerization and antioxidative activity assays. The 35.32%, 26.19% reduction in the worm burden and 33.17%, 31.7% lower liver egg count were obtained in mice vaccinated with rSjPDI compared with the blank control group in two independent trials. Our preliminary results suggest that rSjPDI plays an important role in the development of the schistosome and is a potential vaccine candidate for schistosomiasis.

A review on bovine besnoitiosis: a disease with economic impact in herd health management, caused by Besnoitia besnoiti (Franco and Borges, )

Bovine besnoitiosis is caused by the largely unexplored apicomplexan parasite Besnoitia besnoiti. In cows, infection during pregnancy often results in abortion, and chronically infected bulls become infertile. Similar to other apicomplexans B. besnoiti has acquired a largely intracellular lifestyle, but its complete life cycle is still unknown, modes of transmission have not been entirely resolved and the definitive host has not been identified. Outbreaks of bovine besnoitiosis in cattle were described in the 1990s in Portugal and Spain, and later several cases were also detected in France. More cases have been reported recently in hitherto unaffected countries, including Italy, Germany, Switzerland, Hungary and Croatia. To date, there is still no effective pharmaceutical compound available for the treatment of besnoitiosis in cattle, and progress in the identification of novel targets for intervention through pharmacological or immunological means is hampered by the lack of molecular data on the genomic and transcriptomic level. In addition, the lack of an appropriate small animal laboratory model, and wide gaps in our knowledge on the host-parasite interplay during the life cycle of this parasite, renders vaccine and drug development a cost- and labour-intensive undertaking.

Molecular cloning, expression, and immunolocalization of protein disulfide isomerase in excretory-secretory products from Clonorchis sinensis

Protein disulfide isomerase (PDI) is an essential catalyst of the endoplasmic reticulum with folding and chaperone activities in different biological systems. Here, PDI of Clonorchis sinensis (CsPDI) was isolated from the cDNA library of adult C. sinensis. The open reading frame contains 1,317 bp encoding 438 amino acids and shares 53 %, 49 %, and 43 % identity with PDI from Bos taurus, Homo sapiens, and Schistosoma mansoni, respectively. Two catalytic thioredoxin motifs CxxC were found in this sequence, which were characteristic domains of thioredoxin superfamily. The CsPDI protein was expressed and purified from Escherichia coli BL21 (DE3). According to western blotting analysis, the recombinant CsPDI could be recognized by anti-CsPDI rat serum, anti-excretory/secretory products rat serum, and serum of rat infected with C. sinensis, respectively. Quantitative real-time polymerase chain reaction showed that transcription level of CsPDI in the metacercaria stage was six and four times higher than that in the adult worm and egg stage, respectively. Immunolocalization analysis showed CsPDI could be detected in the intestine, vitellarium, and intrauterine eggs of adult worm, as well as in the cyst wall and vitellarium of metacercaria. In addition, the strong fluorescence signal was observed both on the wall of bile duct and in the lumen of liver tissue of C. sinensis-infected cat. Those results demonstrated that CsPDI was a component of C. sinensis excretory-secretory products. The present study will enhance our understanding of biological functions of CsPDI and pave the way for further studies on host-parasite interaction during C. sinensis infection.

Besnoitia besnoiti protein disulfide isomerase (BbPDI): molecular characterization, expression and in silico modelling

Besnoitia besnoiti is an apicomplexan parasite responsible for bovine besnoitiosis, a disease with a high prevalence in tropical and subtropical regions and re-emerging in Europe. Despite the great economical losses associated with besnoitiosis, this disease has been underestimated and poorly studied, and neither an effective therapy nor an efficacious vaccine is available. Protein disulfide isomerase (PDI) is an essential enzyme for the acquisition of the correct three-dimensional structure of proteins. Current evidence suggests that in Neosporacaninum and Toxoplasmagondii, which are closely related to B. besnoiti, PDI play an important role in host cell invasion, is a relevant target for the host immune response, and represents a promising drug target and/or vaccine candidate. In this work, we present the nucleotide sequence of the B. besnoiti PDI gene. BbPDI belongs to the thioredoxin-like superfamily (cluster 00388) and is included in the PDI_a family (cluster defined cd02961) and the PDI_a_PDI_a'_c subfamily (cd02995). A 3D theoretical model was built by comparative homology using Swiss-Model server, using as a template the crystallographic deduced model of Tapasin-ERp57 (PDB code 3F8U chain C). Analysis of the phylogenetic tree for PDI within the phylum apicomplexa reinforces the close relationship among B. besnoiti, N. caninum and T. gondii. When subjected to a PDI-assay based on the polymerisation of reduced insulin, recombinant BbPDI expressed in E. coli exhibited enzymatic activity, which was inhibited by bacitracin. Antiserum directed against recombinant BbPDI reacted with PDI in Western blots and by immunofluorescence with B. besnoiti tachyzoites and bradyzoites.

Identification of the cross-reactive and species-specific antigens between Neospora caninum and Toxoplasma gondii tachyzoites by a proteomics approach

The characterization of the cross-reactive and species-specific antigens of Neospora caninum and Toxoplasma gondii is important in the exploration to determine the common mechanisms of parasite-host interaction and to improve the serological diagnosis; it is also useful for the selection of the cross-reactive antigens that could be used in the development of vaccines or drugs for controlling the diseases caused by these two parasites. In this study, cross-reactive and species-specific antigens between N. caninum and T. gondii tachyzoites were comprehensively investigated using a proteomics approach with the application of two-dimensional gel electrophoresis, immunoblot analysis, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS), and MALDI-TOF/TOF-MS analysis. Immunoblotting and mass spectrometry analysis revealed that at least 42 individual protein spots of N. caninum were reacted with the anti-N. caninum serum, among which at least 18 protein spots were cross-reacted with the anti-T. gondii serum. Moreover, at least 31 protein spots of T. gondii were reacted with the anti-T. gondii serum, among which at least 19 protein spots were cross-reacted with the anti-N. caninum serum. Furthermore, some new specific proteins were also identified in the N. caninum protein profile by searching Toxoplasma sequences or sequences from other organisms. This study substantiates the usefulness of proteomics in the immunoscreening of the cross-reactive or species-specific antigens of both parasites. In addition, the present study showed that there was significant homology in the antigenic proteome profiles between the two parasites. These observations have implications for the design of multicomponent common vaccines against both parasite infections.

A high-throughput turbidometric assay for screening inhibitors of Leishmania major protein disulfide isomerase

The use of a high-throughput technique to perform a pilot screen for Leishmania major protein disulfide isomerase (LmPDI) inhibitors identification is reported. In eukaryotic cells, protein disulfide isomerase (PDI) plays a crucial role in protein folding by catalyzing the rearrangement of disulfide bonds in substrate proteins following their synthesis. LmPDI displays similar domain structure organization and functional properties to other PDI family members and is involved in Leishmania virulence. The authors used a method based on the enzyme-catalyzed reduction of insulin in the presence of dithiothreitol. The screen of a small library of 1920 compounds was performed in a 384-well format and led to the identification of 27 compounds with inhibitory activity against LmPDI. The authors further tested the cytotoxicity of these compounds using Jurkat cells as well as their effect on Leishmania donovani amastigotes using high-content analysis. Results show hexachlorophene and a mixture of theaflavin monogallates inhibit Leishmania multiplication in infected macrophages derived from THP-1 cells, although the inhibitory effect on LmPDI enzymatic activity does not necessarily correlate with the antileishmanial activity.

Intraperitoneal and intra-nasal vaccination of mice with three distinct recombinant Neospora caninum antigens results in differential effects with regard to protection against experimental challenge with Neospora caninum tachyzoites

Recombinant NcPDI(recNcPDI), NcROP2(recNcROP2), and NcMAG1(recNcMAG1) were expressed in Escherichia coli and purified, and evaluated as potential vaccine candidates by employing the C57Bl/6 mouse cerebral infection model. Intraperitoneal application of these proteins suspended in saponin adjuvants lead to protection against disease in 50% and 70% of mice vaccinated with recNcMAG1 and recNcROP2, respectively, while only 20% of mice vaccinated with recNcPDI remained without clinical signs. In contrast, a 90% protection rate was achieved following intra-nasal vaccination with recNcPDI emulsified in cholera toxin. Only 1 mouse vaccinated intra-nasally with recNcMAG1 survived the challenge infection, and protection achieved with intra-nasally applied recNcROP2 was at 60%. Determination of cerebral parasite burdens by real-time PCR showed that these were significantly reduced only in recNcROP2-vaccinated animals (following intraperitoneal and intra-nasal application) and in recNcPDI-vaccinated mice (intra-nasal application only). Quantification of viable tachyzoites in brain tissue of intra-nasally vaccinated mice showed that immunization with recNcPDI resulted in significantly decreased numbers of live parasites. These data show that, besides the nature of the antigen, the protective effect of vaccination also depends largely on the route of antigen delivery. In the case of recNcPDI, the intra-nasal route provides a platform to generate a highly protective immune response.

Neospora caninum--how close are we to development of an efficacious vaccine that prevents abortion in cattle?

Neospora caninum is a protozoan parasite that causes abortion in cattle around the world. Although the clinical signs of disease in both dogs and cattle have now been recognised for over 20years, treatment and control options are still limited, despite the availability of a commercial vaccine in some countries of the world. The case for an efficacious vaccine has not been convincingly waged by farmers, veterinarians and other members of the agricultural and rural communities. In recent times, however, economic modelling has been used to estimate the industry losses due to Neospora-associated abortion, providing, in turn, the business case for forms of control for this parasite, including the development of vaccines. In this review, we document progress in all areas of the vaccine development pipeline, including live, killed and recombinant forms and the animal models available for vaccine evaluation. In addition, we summarise the main outcomes on the economics of Neospora control and suggest that the current boom in the global dairy industry increases the specific need for a vaccine against N. caninum-associated abortion.

Identification and enzymatic activities of four protein disulfide isomerase (PDI) isoforms of Leishmania amazonensis

Leishmania parasites primarily infect cells of macrophage lineage and can cause leishmaniasis in the skin, mucosal, and visceral organs, depending on both host- and parasite-derived factors. The protein disulfide isomerases (PDIs) are thiol-disulfide oxidoreductases that catalyze the formation, reduction, and isomerization of disulfide bonds of proteins in cells. Although four Leishmania PDI genes are functionally inferred from homology in the genome sequences, only two of them have been expressed as active proteins to date. The functional relationship among various PDI enzymes remains largely unclear. In this study, we expressed and partially characterized all four L. amazonensis PDIs encoding 52-, 47-, 40-, and 15-kDa proteins. Homology analysis showed that the sequence identity between L. amazonensis (New World) PDIs and their counterpart PDI sequences from L. major (Old World) ranged from 76% to 99%. Kinetic characterization indicated that while the 15-, 40-, and 47- kDa PDI proteins displayed both insulin isomerase and reductase activities, the 52-kDa protein had only isomerase activity with no detectable reductase activity. All four PDI proteins were recognized by sera from L. amazonensis-infected mice and were sensitive to inhibition by standard PDI inhibitors. This study describes the enzymatic activities of recombinant L. amazonensis PDIs and suggests a role for these proteins in parasite development.

Neospora caninum: functional inhibition of protein disulfide isomerase by the broad-spectrum anti-parasitic drug nitazoxanide and other thiazolides

Nitazoxanide (NTZ) and several NTZ-derivatives (thiazolides) have been shown to exhibit considerable anti-Neospora caninum tachyzoite activity in vitro. We coupled tizoxanide (TIZ), the deacetylated metabolite, to epoxy-agarose-resin and performed affinity chromatography with N. caninum tachyzoite extracts. Two main protein bands of 52 and 43kDa were isolated. The 52kDa protein was readily recognized by antibodies directed against NcPDI, and mass spectrometry confirmed its identity. Poly-histidine-tagged NcPDI-cDNA was expressed in Escherichia coli and recombinant NcPDI (recNcPDI) was purified by Co2+-affinity chromatography. By applying an enzyme assay based on the measurement of insulin crosslinking activity, recNcPDI exhibited properties reminiscent for PDIs, and its activity was impaired upon the addition of classical PDI inhibitors such as bacitracin (1-2mM), para-chloromercuribenzoic acid (0.1-1mM) and tocinoic acid (0.1-1mM). RecNcPDI-mediated insulin crosslinking was inhibited by NTZ (5-100 microM) in a dose-dependent manner. In addition, the enzymatic activity of recNcPDI was inhibited by those thiazolides that also affected parasite proliferation. Thus, thiazolides readily interfere with NcPDI, and possibly also with PDIs from other microorganisms susceptible to thiazolides.

Identification of three protein disulfide isomerase members from Haemaphysalis longicornis tick

Three genes encoding putative protein disulfide isomerase (PDI) were isolated from the Haemaphysalis longicornis EST database and designed as HlPDI-1, HlPDI-2, and HlPDI-3. All three PDI genes contain two typical PDI active sites CXXC and encode putative 435, 499, and 488 amino acids, respectively. The recombinant proteins expressed in Escherichia coli all show PDI activities, and the activities were inhibited by a PDI-specific inhibitor, zinc bacitracin. Western blot analysis and real-time PCR revealed that three HlPDIs were present in all the developmental stages of the tick as well as in the midgut, salivary glands, ovary, hemolymph, and fatbody of adult female ticks, but the three genes were expressed at the highest level in the egg stage. HlPDI-1 is expressed primarily in the ovary and secondarily in the salivary glands. HlPDI-2 and HlPDI-3 are expressed primarily in the salivary gland, suggesting that the PDI genes are important for tick biology, especially for egg development, and that they play distinct roles in different tissues. Blood feeding induced significantly increased expression of HlPDI-1 and HlPDI-3 in both partially fed nymphs and adults. Babesia gibsoni-infected larval ticks expressed HlPDI-1 and HlPDI-3 2.0 and 4.0 times higher than uninfected normal larval ticks, respectively. The results indicate that HlPDI-1 and HlPDI-3 might be involved in tick blood feeding and Babesia parasite infection in ticks.