Molecular characterization of two myoglobins of Paragonimus westermani

Evolutionary Adaptations of Parasitic Flatworms to Different Oxygen Tensions

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

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.

De novo genome and transcriptome analyses provide insights into the biology of the trematode human parasite Fasciolopsis buski

Many trematode parasites cause infection in humans and are thought to be a major public health problem. Their ecological diversity in different regions provides challenging questions on evolution of these organisms. In this report, we perform transcriptome analysis of the giant intestinal fluke, Fasciolopsis buski, using next generation sequencing technology. Short read sequences derived from polyA containing RNA of this organism were assembled into 30,677 unigenes that led to the annotation of 12,380 genes. Annotation of the assembled transcripts enabled insight into processes and pathways in the intestinal fluke, such as RNAi pathway and energy metabolism. The expressed kinome of the organism was characterized by identifying all protein kinases. A rough draft genome assembly for Fasciolopsis buski is also reported herewith with SRA accessions for crosschecking the findings in the analyzed transcriptome data. Transcriptome data also helped us to identify some of the expressed transposable elements. Though many Long Interspersed elements (LINEs) were identified, only two Short Interspersed Elements (SINEs) were visible. Overall transcriptome and draft genome analysis of F. buski helped us to characterize some of its important biological characteristics and provided enormous resources for development of a suitable diagnostic system and anti-parasitic therapeutic molecules.

Molecular characterization of Clonorchis sinensis secretory myoglobin: delineating its role in anti-oxidative survival

Background

Clonorchiasis is a globally important, neglected food-borne disease caused by Clonorchis sinensis (C. sinensis), and it is highly related to cholangiocarcinoma and hepatocellular carcinoma. Increased molecular evidence has strongly suggested that the adult worm of C. sinensis continuously releases excretory-secretory proteins (ESPs), which play important roles in the parasite-host interactions, to establish successful infection and ensure its own survival. Myoglobin, a hemoprotein, is present in high concentrations in trematodes and ESPs. To further understand the biological function of CsMb and its putative roles in the interactions of C. sinensis with its host, we explored the molecular characterization of CsMb in this paper.

Methods

We expressed CsMb and its mutants in E. coli BL21 and identified its molecular characteristics using bioinformatics analysis and experimental approaches. Reverse transcription PCR analysis was used to measure myoglobin transcripts of C. sinensis with different culture conditions. The peroxidase activity of CsMb was confirmed by spectrophotometry. We co-cultured RAW264.7 cells with recombinant CsMb (rCsMb), and we then measured the production of hydrogen peroxide (H₂O₂) and nitric oxide (NO) in addition to the mRNA levels of inducible nitric oxide synthase (iNOS), Cu-Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD2) in activated RAW264.7 cells.

Results

In the in vitro culture of adult worms, the transcripts of CsMb increased with the increase of oxygen content. Oxidative stress conditions induced by H₂O₂ increased the levels of CsMb transcripts in a dose-dependent manner. Furthermore, CsMb catalyzed oxidation reactions in the presence of H₂O₂, and amino acid 34 of CsMb played an essential role in its reaction with H₂O₂. In addition, CsMb significantly reduced H₂O₂ and NO levels in LPS-activated macrophages, and CsMb downregulated iNOS and SOD expression in activated macrophages.

Conclusion

The present study is the first to investigate the peroxidase activity of CsMb. This investigation suggested that C. sinensis may decrease the redox activation of macrophages by CsMb expression to evade host immune responses. These studies contribute to a better understanding of the role of CsMb in the molecular mechanisms involved in ROS detoxification by C. sinensis.

Fasciola hepatica and Schistosoma mansoni: identification of common proteins by comparative proteomic analysis

It is not unusual to find common molecules among parasites of different species, genera, or phyla. When those molecules are antigenic, they may be used for developing drugs or vaccines that simultaneously target different species or genera of parasite. In the present study, we used a proteomic-based approach to identify proteins that are common to adult Fasciola hepatica and Schistosoma mansoni. Whole-worm extracts from each parasite were separated by 2-dimensional electrophoresis (2-DE), and digital images of both proteomes were superimposed using imaging software to identify proteins with identical isoelectric points and molecular weights. Protein identities were determined by mass spectrometry. Imaging and immunoblot analyses identified 28 immunoreactive proteins that are common to both parasites. Among these molecules are antioxidant proteins (thioredoxin and glutathione-S-transferase), glycolytic enzymes (glyceraldehyde 6-phosphate dehydrogenase and enolase), proteolytic enzymes (cathepsin-L and -D), inhibitors (Kunitz-type, Stefin-1), proteins with chaperone activity (heat shock protein 70 and fatty acid-binding protein), and structural proteins (calcium-binding protein, actin, and myosin). Some of the identified proteins could be used to develop drugs and vaccines against fascioliasis and schistosomiasis.

The hemoglobins of the trematodes Fasciola hepatica and Paramphistomum epiclitum: a molecular biological, physico-chemical, kinetic, and vaccination study

The trematode Fasciola hepatica (Fa.he.) is a common parasite of human and livestock. The hemoglobin (Hb) of Fa.he., a potential immunogen, was chosen for characterization in the search for an effective vaccine. Characterization of trematode Hbs show that they are intracellular single-domain globins with the following remarkable features: (1) Fa.he. expresses two Hb isoforms that differ at two amino acid sites (F1: 119Y/123Q; F2: 119F/123L). Both isoforms are monoacetylated at their N-termini; (2) the genes coding for Fa.he. and Paramphistomum epiclitum (Pa.ep.) Hbs are interrupted by two introns at the conserved positions B12.2 and G7.0.; (3) UV/VIS and resonance Raman spectroscopy identify the recombinant Fa.he. HbF2 as a pentacoordinated high-spin ferrous Hb; (4) electron paramagnetic resonance spectroscopy of cyano-met Fa.he. HbF2 proves that the endogenously bound imidazole has no imidazolate character; (5) the major structural determinants of the globin fold are present, they contain a TyrB10/TyrE7 residue pair on the distal side. Although such distal-site pair is a signature for high oxygen affinity, as shown for Pa.ep. Hb, the oxygen-binding rate parameters for Fa.he. Hb are intermediate between those of myoglobin and those of other trematode Hbs; (6) the three-dimensional structure of recombinant Fa.he. HbF2 from this study closely resembles the three-dimensional structure of Pa.ep. determined earlier. The set of distal-site polar interactions observed in Pa.ep. Hb is matched with small but significant structural adjustments; (7) despite the potential immunogenic character of the fluke Hb, vaccination of calves with recombinant Fa.he. HbF2 failed to promote protection against parasitic infection.