Venom allergen-like protein 28 in Clonorchis sinensis: four epitopes on its surface and the potential role of Cys124 for its conformational stability

Venom allergen-like (VAL) proteins are important to host-parasite interactions. We previously demonstrated that a Clonorchis sinensis VAL (CsVAL) protein-derived synthetic peptide suppresses allergic and inflammatory responses. However, little is known regarding the physicochemical and antigenic properties of CsVAL proteins. Here, we identified a novel 194 amino acid VAL protein, named C. sinensis VAL 28 (CsVAL28), and characterized its functional motifs and structural details as a new member of the CAP superfamily. Unlike members of the Schistosoma mansoni VAL (SmVAL) family, CsVAL28 has a single CAP1 motif and six highly conserved disulfide bond-forming cysteines. Tertiary models of wild-type CsVAL28 and mutants were built using SmVAL4 as template via homology modeling. Normal mode analysis predicted that disulfide bond breaking by mutation of cysteine 124 to serine would greatly affect protein mobility. Four major immunoreactive linear epitopes were identified in the surface-exposed region or its vicinity via epitope mapping, using sera from clonorchiasis patients and healthy controls. Our findings provide in-depth knowledge on the structure-function properties of VAL proteins and may help determine highly antigenic regions for developing new diagnostic approaches.

Oral delivery of Bacillus subtilis spores expressing cysteine protease of Clonorchis sinensis to grass carp (Ctenopharyngodon idellus): Induces immune responses and has no damage on liver and intestine function

Clonorchis sinensis (C. sinensis) is a fish-borne trematode. Human can be infected by ingestion of C. sinensis metacercariae parasitized in grass carp (Ctenopharyngodon idella). For induction of effective oral immune responses, spores of Bacillus subtilis (B. subtilis) WB600 were utilized as vehicle to delivery CsCP (cysteine protease of C. sinensis) cooperated with CotC (B.s-CotC-CP), one of coat proteins, to the gastrointestinal tract. After routine culture of 8-12 h in LB medium, B. subtilis containing CotC-CsCP was transferred into the sporulation culture medium. SDS-PAGE, western blotting and the growth curve indicated that the best sporulation time of recombinant WB600 was 24-30 h at 37 °C with continuous shaking (250 rpm). Grass carp were fed with three levels of B.s-CotC-CP (1 × 10⁶, 1 × 10⁷, and 1 × 10⁸ CFU g^-1) incorporated in the basal pellets diet. The commercial pellets or supplemented with spores just expressing CotC (1 × 10⁷ CFU g^-1) were served as control diet. Our results showed that grass carp orally immunized with the feed-based B.s-CotC-CP developed a strong specific immune response with significantly (P < 0.05) higher levels of IgM in samples of serum, bile, mucus of surface and intestinal compared to the control groups. Abundant colonization spores expressing CsCP were found in hindgut that is conducive to absorption and presentation of antigen. Moreover, B. subtilis spores appeared to show no sign of toxicity or damage in grass carp. Our cercariae challenge experiments suggested that oral administration of spores expressing CsCP could develop an effective protection against C. sinensis in fish body. Therefore, this study demonstrated that the feed-based recombinant spores could trigger high levels of mucosal and humoral immunity, and would be a promising candidate vaccine against C. sinensis metacercariae formation in freshwater fish.

[Purification of Clonorchis sinensis native protein and their application in immunodiagnosis of clonorchiasis]

Lots of purified antigens have been obtained from crude antigens of Clonorchis sinensis. Some of them have applied to immunodiagnosis of clonorchiasis in laboratory. Here, we review purification methods, diagnostic efficacy and application prospect of purified antigens.

Molecular cloning, expression, and immunolocalization of the NAD(+)-dependent glycerol 3-phosphate dehydrogenase (GPD) from Clonorchis sinensis

Glycerol 3-phosphate dehydrogenase (GPD) plays an important role in the energy metabolism and nutrition metabolism. In order to know about the biological functions of GPD of Clonorchis sinensis (C. sinensis), we identified a complete gene coding GPD from C. sinensis metacercaria cDNA library. This novel cDNA sequence contains 1,056 bp with a putative open reading frame of 351 amino acids and shares 74% identity with GPD from Schistosoma mansoni. Recombinant CsGPD was expressed and purified from Escherichia coli BL21 (DE3). Western blot analysis displayed that recombinant CsGPD can be recognized by anti-CsGPD serum and C. sinensis-infected serum. RT-PCR and immunolocalization analysis confirmed that GPD expressed both at the stage of adult worm and metacercaria of C. sinensis and immunolocated at the tegument of adult worm, tegument and tegumentary cells of metacercaria. Our current study has paved the way for the further researches about the biological functions involved in the growth of C. sinensis.

Clonorchis sinensis: molecular cloning, enzymatic activity, and localization of yolk ferritin

Ferritin is an intracellular protein that is involved in iron metabolism. A cDNA clone of Clonorchis sinensis (CsFtn), 565 bp long, encoded a putative polypeptide of 166 amino acids. CsFtn cDNA revealed a putative loop-stem structure similar to iron-responsive element (IRE). CsFtn polypeptide appeared homologous to the ferritin of trematodes with high sequential identity. Phylogenetic tree analysis showed that CsFtn clustered with the ferritins of other flukes. Recombinant CsFtn protein was produced and purified from an Escherichia coli system, and immune mouse serum was raised against CsFtn. Recombinant CsFtn showed iron-uptake ability. In adult C. sinensis, CsFtn protein was found to localize in vitelline follicles and eggs. Based on these results, CsFtn cDNA is considered to encode a C. sinensis yolk ferritin.

Clonorchis sinensis: codon usage in nuclear genes

Codon usage in Clonorchis sinensis was analyzed using 12,515 codons from 38 coding sequences. Total GC content was 49.83%, and GC1, GC2 and GC3 contents were 56.32%, 43.15% and 50.00%, respectively. The effective number of codons converged at 51-53 codons. When plotted against total GC content or GC3, codon usage was distributed in relation to GC3 biases. Relative synonymous codon usage for each codon revealed a single major trend, which was highly correlated with GC content at the third position when codons began with A or U at the first two positions. In codons beginning with G or C base at the first two positions, the G or C base rarely occurred at the third position. These results suggest that codon usage is shaped by a bias towards G or C at the third base, and that this is affected by the first and second bases.

MOLECULAR CLONING AND CHARACTERIZATION OF VITELLINE PRECURSOR PROTEIN B1 FROM CLONORCHIS SINENSIS

In trematodes, vitelline precursor proteins are required for eggshell formation. A cDNA clone of Clonorchis sinensis (CsVpB1) was selected from an EST pool, encoding a polypeptide of 245 amino acids. The CsVpB1 polypeptide demonstrated homology with vitelline precursor proteins from trematodes with high sequential identities. In a phylogenic tree, CsVpB1 clustered with trematode VpB proteins. The CsVpB1 polypeptide was found to be rich in tyrosine residues, including putative predihydroxyphenyl alanine (DOPA) residues, involved in cross-linking of the precursor proteins. Mouse immune sera were raised against a recombinant CsVpB1 protein. In adult C. sinensis, CsVpB1 protein was exclusively localized in vitelline follicles. Based on these results, the CsVpB1 cDNA is believed to encode a VpB of C. sinensis.

Molecular cloning and immunolocalization of the 17 kDa myoglobin of Clonorchis sinensis

We purified the 17 kDa protein abundant in Clonorchis sinensis crude extracts. The N-terminal amino acid sequence of this protein was determined and an oligonucleotide probe synthesized. Using this probe, the cDNA encoding the protein was cloned and sequenced from the C. sinensis cDNA library. It was found to consist of a total of 150 amino acids and to have 41% conserved homology with the myoglobin of the trematodes Paramphistomum epiclitum and Isoparorchis hypselobagri. The gene product over-expressed in the bacterial system was purified and identified as the same molecule in the adult worms. BALB/c mouse sera raised against the adult 17 kDa protein revealed that this myoglobin was distributed throughout the parenchymal tissues except for the eggs and reproductive organs and that the protein may be involved in the survival of C. sinensis in the oxygen-depleted environment of the host.

Clonorchis sinensis tropomyosin: cloning and sequence of partial cDNA amplified by PCR

C. sinensis total RNA was containing large amount of 18S rRNA but little 28S rRNA. The size of the double-stranded cDNA synthesized from poly (A)+ mRNA was 0.4-4.2 kb long with tapering upto 9.5 kb. Degenerated oligonucleotides (as 2 sense and 3 antisense primers) were designed on the conserved regions of the known tropomyosin amino acid sequences. From one out of the PCR amplifications using total cDNA and matrix of primers, a specific gene product, 580 bp in size, was produced. Upon Southern hybridization of the PCR products with Schistosoma mansoni tropomyosin (SMTM) cDNA, only one signal appeared at the band of 580 bp product. This 580 bp product was considered to encode C. sinensis tropomyosin (CSTM) and cloned in pGEM-3Zf(-) for DNA sequencing. CSTM cDNA was 575 bp containing one open reading frame of 191 predicted amino acids, which revealed 86.3% homology with SMTM and 51.1% with Trichostrongylus colubriformis tropomyosin. CSTM cDNA obtained will serve as a probe in the studies of molecular cloning of CSTM.