Molecular characterization and immunolocalization of a protein disulfide isomerase from Angiostrongylus cantonensis

Identification and Characterization of a Novel Protein Disulfide Isomerase Gene (MgPDI2) from Meloidogyne graminicola

Protein disulfide isomerase (PDI) is a multifunctional enzyme that catalyzes rate-limiting reactions such as disulfide bond formation, isomerization, and reduction. There is some evidence that indicates that PDI is also involved in host-pathogen interactions in plants. In this study, we show that the rice root-knot nematode, Meloidogyne graminicola, has evolved a secreted effector, MgPDI2, which is expressed in the subventral esophageal glands and up-regulated during the early parasitic stage of M. graminicola. Purified recombinant MgPDI2 functions as an insulin disulfide reductase and protects plasmid DNA from nicking. As an effector, MgPDI2 contributes to nematode parasitism. Silencing of MgPDI2 by RNA interference in the pre-parasitic second-stage juveniles (J2s) reduced M. graminicola multiplication and also increased M. graminicola mortality under H2O2 stress. In addition, an Agrobacterium-mediated transient expression assay found that MgPDI2 caused noticeable cell death in Nicotiana benthamiana. An intact C-terminal region containing the first catalytic domain (a) with an active motif (Cys-Gly-His-Cys, CGHC) and the two non-active domains (b and b') is required for cell death induction in N. benthamiana. This research may provide a promising target for the development of new strategies to combat M. graminicola infections.

Meloidogyne graminicola protein disulfide isomerase may be a nematode effector and is involved in protection against oxidative damage

The rice root-knot nematode, Meloidogyne graminicola, is a serious pest in most rice-growing countries. Usually, nematodes employ antioxidants to counteract the harm of reactive oxygen species (ROS) and facilitate their infection. Here the gene encoding M. graminicola protein disulphide isomerase (MgPDI) was identified. The deduced protein is highly conserved in the putative active-site Cys-Gly-His-Cys. In situ hybridization showed that MgPDI was specifically localized within esophageal glands of pre-parasitic second stage juveniles (J2s). MgPDI was significantly up-regulated in the late parasitic J2s. Characterization of the recombinant protein showed that the purified MgPDI exhibited similar activities to other oxidases/isomerases such as the refolding of the scrambled RNase and insulin disulfide reductase and the protection of plasmid DNA and living cells from ROS damage. In addition, silencing of MgPDI by RNA interference in the pre-parasitic J2s lowered their multiplication factor. MgPDI expression was up-regulated in the presence of exogenous H2O2, whereas MgPDI silencing resulted in an increase in mortality under H2O2 stress. MgPDI is localized in the apoplast when transient expression in Nicotiana benthamiana leaves. The results indicated that MgPDI plays important roles in the reproduction and pathogenicity of M. graminicola and it also contributes to protecting nematodes from exogenous H2O2 stress.

Molecular cloning and characterization of protein disulfide isomerase of Brugia malayi, a human lymphatic filarial parasite

Lymphatic filariasis results in an altered lymphatic system and the abnormal enlargement of body parts, causing pain, serious disability and social stigma. Effective vaccines are still not available nowadays, drugs against the disease is required. Protein disulfide isomerase (PDI) is an essential catalyst of the endoplasmic reticulum which is involved in folding and chaperone activities in different biological systems. Here, we report the enzymatic characterization of a Brugia malayi Protein disulfide isomerase (BmPDI), which was expressed and purified from Escherichia coli BL21 (DE3). Western blotting analysis showed the recombinant BmPDI could be recognized by anti-BmPDI Rabbit serum. The rBmPDI exhibited an optimum activity at pH 8 and 40 °C. The enzyme was inhibited by aurin and PDI inhibitor. Recombinant BmPDI showed interaction with recombinant Brugia malayi calreticulin (rBmCRT). The three-dimensional model for BmPDI and BmCRT was generated by homology modelling. A total of 25 hydrogen bonds were found to be formed between two interfaces. There are 259 non-bonded contacts present in the BmPDI-BmCRT complex and 12 salt bridges were formed in the interaction.

Cloning and expression of a 16-kDa recombinant protein from Angiostrongylus cantonensis for use in immunoblot diagnosis of human angiostrongyliasis

Angistrongylus cantonensis is a zoonotic nematode parasite and causative agent of human angiostrongyliasis, which clinically presents as eosinophilic meningitis or meningoencephalitis. Diagnosis of the disease is problematic since parasitologic findings are infrequent, and infection determinations must be based on the clinical symptoms and serological tests with limited specificities and sensitivities. The aim of the present study was to identify and generate a novel recombinant protein from A. cantonensis and evaluate its efficacy in the diagnosis of human angiostrongyliasis when incorporated into a Western blot serodiagnostic system. A cDNA protein expression library from adult A. cantonensis was constructed, followed by immunoscreening with serum from confirmed infected patients to identify and isolate immunoreactive clones. One clone, designated fAC40, possessed a partial sequence encoding a LisH protein domain with a predicted molecular weight of 16 kDa and containing four predicted antigenic peptides. By incorporating recombinant fAC40 in Western immunoblot tests using a serum panel consisting of confirmed and clinically diagnosed cases of human angiostrongyliasis and other helminthic infections, fAC40 exhibited a sensitivity and specificity of 91.8 and 100 %, respectively, and a positive and negative predictive value of 100 and 97.19 %, respectively, in the diagnosis of angiostrongyliasis. Importantly, it was not reactive with antibodies from serum of patients infected with Gnathostoma spinigerum and Cysticercus cellulosae, infections that clinically present neurological symptoms similar to angiostrongyliasis. These data demonstrate that the 16-kDa recombinant protein from A. cantonensis possesses high potential as a candidate antigen for a more sensitive and specific serodiagnosis of human angiostrongyliasis.

Identification and characterisation of microRNAs in young adults of Angiostrongylus cantonensis via a deep-sequencing approach

Angiostrongylus cantonensis is an important causative agent of eosinophilic meningitis and eosinophilic meningoencephalitis in humans. MicroRNAs (miRNAs) are small non-coding RNAs that participate in a wide range of biological processes. This study employed a deep-sequencing approach to study miRNAs from young adults of A. cantonensis. Based on 16,880,456 high-quality reads, 252 conserved mature miRNAs including 10 antisense miRNAs that belonging to 90 families, together with 10 antisense miRNAs were identified and characterised. Among these sequences, 53 miRNAs from 25 families displayed 50 or more reads. The conserved miRNA families were divided into four groups according to their phylogenetic distribution and a total of nine families without any members showing homology to other nematodes or adult worms were identified. Stem-loop real-time polymerase chain reaction analysis of aca-miR-1-1 and aca-miR-71-1 demonstrated that their level of expression increased dramatically from infective larvae to young adults and then decreased in adult worms, with the male worms exhibiting significantly higher levels of expression than female worms. These findings provide information related to the regulation of gene expression during the growth, development and pathogenesis of young adults of A. cantonensis.

Molecular cloning, expression, and characterization of a putative activation-associated secreted protein from Angiostrongylus cantonensis

Activation-associated secreted protein (ASP) had been found in many helminthes, which was associated with pathogenesis and stage transition. A complementary DNA (cDNA) sequence encoding a putative two-domain ASP was obtained from an Angiostrongylus cantonensis fourth-stage larvae cDNA library, which we designated as AgASP. The cDNA of AgASP contains an open reading frame encoding 424 amino acids, the first 19 residues being a putative secretion signal. The expression pattern of this protein was investigated by real-time polymerase chain reaction and Western blot. We found that this protein expressed most highly in the brain-stage larvae (Lbr) of this parasite and existed in the excretory/secretory products of this stage. Immunofluorescence showed it existed in the lumen of the Lbr. The recombinant protein can be recognized by the infection sera from mice (nonpermissive host), while it cannot be recognized by infection sera from rats (permissive host). The infiltration of neutrophils in infected nonpermissive host can be lessened by immunizing this host with this protein (immunized vs control group, 13.7 ± 10.2 vs 65.5 ± 19.2). These findings suggest that this protein plays a role in the pathogenesis of human angiostrongyliasis and is worthy of further study.