FhCaBP4: a Fasciola hepatica calcium-binding protein with EF-hand and dynein light chain domains

Qualitative analysis of Fasciola gigantica excretory and secretory products coimmunoprecipitated with buffalo secondary infection sera shows dissimilar components from primary infection sera

Buffaloes cannot mount a robust adaptive immune response to secondary infection by Fasciola gigantica. Even if excretory and secretory products (ESPs) exhibit potent immunoregulatory effects during primary infection, research on ESPs in secondary infection is lacking, even though the ESP components that are excreted/secreted during secondary infection are unknown. Therefore, qualitative analysis of ESP during secondary infection was performed and compared with that of primary infection to deepen the recognition of secondary infection and facilitate immunoregulatory molecules screening. Buffaloes were divided into three groups: A (n = 3, noninfected), B (n = 3, primary infection) and C (n = 3, secondary infection). Buffaloes in the primary (0 weeks post infection; wpi) and secondary (-4 and 0 wpi) infection groups were infected with 250 metacercariae by oral administration. Then, sera were collected from groups at different wpi, and interacting proteins were precipitated by coimmunoprecipitation (Co-IP), qualitatively analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and annotated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to infer their potential functions. In group C, 324 proteins were identified, of which 76 proteins were consistently identified across 7 time points (1, 3, 6, 8, 10, 13, and 16 wpi). Compared with 87 proteins consistently identified in group B, 22 proteins were identified in group C. Meanwhile, 34 proteins were only identified in group C compared to 200 proteins identified in group B. Protein pathway analysis indicated that these proteins were mainly involved in the cellular processes and metabolism of F. gigantica. Among them, 14-3-3θ was consistently identified in group C and may be involved in various cellular processes and innate immune signalling pathways. Members of the HSP family were identified in both groups B and C and may function in both primary and secondary infection processes. The proteins discovered in the present study will help to deepen the understanding of the molecular interactions between F. gigantica and buffalo during secondary infection and facilitate the identification of new potential immunoregulatory molecules.

Protective human IgE responses are promoted by comparable life-cycle dependent Tegument Allergen-Like expression in Schistosoma haematobium and Schistosoma mansoni infection

Schistosoma haematobium is the most prevalent of the human-infecting schistosome species, causing significant morbidity in endemically exposed populations. Despite this, it has been relatively understudied compared to its fellow species, S. mansoni. Here we provide the first comprehensive characterization of the S. haematobium Tegument Allergen-Like protein family, a key protein family directly linked to protective immunity in S. mansoni infection. Comparable with observations for S. mansoni, parasite phylogenetic analysis and relative gene expression combined with host serological analysis support a cross-reactive relationship between S. haematobium TAL proteins, exposed to the host immune system as adult worms die, and closely related proteins, exposed during penetration by the infecting cercarial and early schistosomulae stages. Specifically, our results strengthen the evidence for host immunity driven by cross-reactivity between family members TAL3 and TAL5, establishing it for the first time for S. haematobium infection. Furthermore, we build upon this relationship to include the involvement of an additional member of the TAL protein family, TAL11 for both schistosome species. Finally, we show a close association between experience of infection and intensity of transmission and the development of protective IgE responses to these antigens, thus improving our knowledge of the mechanisms by which protective host immune responses develop. This knowledge will be critical in understanding how control efforts such as mass drug administration campaigns influence the development of host immunity and subsequent patterns of infection and disease within endemic populations.

The Schistosoma mansoni tegumental allergen protein, SmTAL1: Binding to an IQ-motif from a voltage-gated ion channel and effects of praziquantel

SmTAL1 is a calcium binding protein from the parasitic worm, Schistosoma mansoni. Structurally it is comprised of two domains - an N-terminal EF-hand domain and a C-terminal dynein light chain (DLC)-like domain. The protein has previously been shown to interact with the anti-schistosomal drug, praziquantel (PZQ). Here, we demonstrated that both EF-hands in the N-terminal domain are functional calcium ion binding sites. The second EF-hand appears to be more important in dictating affinity and mediating the conformational changes which occur on calcium ion binding. There is positive cooperativity between the four calcium ion binding sites in the dimeric form of SmTAL1. Both the EF-hand domain and the DLC-domain dimerise independently suggesting that both play a role in forming the SmTAL1 dimer. SmTAL1 binds non-cooperatively to PZQ and cooperatively to an IQ-motif from SmCa_v1B, a voltage-gated calcium channel. PZQ tends to strengthen this interaction, although the relationship is complex. These data suggest the hypothesis that SmTAL1 regulates at least one voltage-gated calcium channel and PZQ interferes with this process. This may be important in the molecular mechanism of this drug. It also suggests that compounds which bind SmTAL1, such as six from the Medicines for Malaria Box identified in this work, may represent possible leads for the discovery of novel antagonists.

The tegumental allergen-like proteins of Schistosoma mansoni: A biochemical study of SmTAL4-TAL13

Schistosoma mansoni, like other trematodes, expresses a number of unusual calcium binding proteins which consist of an EF-hand domain joined to a dynein light chain-like (DLC-like) domain by a flexible linker. These proteins have been implicated in host immune responses and drug binding. Three members of this protein family from S. mansoni (SmTAL1, SmTAL2 and SmTAL3) have been well characterised biochemically. Here we characterise the remaining family members from this species (SmTAL4-13). All of these proteins form homodimers and all except SmTAL5 bind to calcium and manganese ions. SmTAL9, 10 and 11 also bind to magnesium ions. The antischistosomal drug, praziquantel interacts with SmTAL4, 5 and 8. Some family members also bind to calmodulin antagonists such as chlorpromazine and trifluoperazine. Molecular modelling suggests that all ten proteins adopt similar overall folds with the EF-hand and DLC-like domains folding discretely. Bioinformatics analyses suggest that the proteins may fall into two main categories: (i) those which bind calcium ions reversibly at the second EF-hand and may play a role in signalling (SmTAL1, 2, 8 and 12) and (ii) those which bind calcium ions at the first EF-hand and may play either signalling or structural roles (SmTAL7, 9, 10 and 13). The remaining proteins include those which do not bind calcium ions (SmTAL3 and 5) and three other proteins (SmTAL4, 6 and 11). The roles of these proteins are less clear, but they may also have structural roles.

A mysterious family of calcium-binding proteins from parasitic worms

There is a family of proteins from parasitic worms which combine N-terminal EF-hand domains with C-terminal dynein light chain-like domains. Data are accumulating on the biochemistry and cell biology of these proteins. However, little is known about their functions in vivo Schistosoma mansoni expresses 13 family members (SmTAL1-SmTAL13). Three of these (SmTAL1, SmTAL2 and SmTAL3) have been subjected to biochemical analysis which demonstrated that they have different molecular properties. Although their overall folds are predicted to be similar, small changes in the EF-hand domains result in differences in their ion binding properties. Whereas SmTAL1 and SmTAL2 are able to bind calcium (and some other) ions, SmTAL3 appears to be unable to bind any divalent cations. Similar biochemical diversity has been seen in the CaBP proteins from Fasciola hepatica Four family members are known (FhCaBP1-4). All of these bind to calcium ions. However, FhCaBP4 dimerizes in the presence of calcium ions, FhCaBP3 dimerizes in the absence of calcium ions and FhCaBP2 dimerizes regardless of the prevailing calcium ion concentration. In both the SmTAL and FhCaBP families, the proteins also differ in their ability to bind calmodulin antagonists and related drugs. Interestingly, SmTAL1 interacts with praziquantel (the drug of choice for treating schistosomiasis). The pharmacological significance (if any) of this finding is unknown.

FhCaBP1 (FH22): A Fasciola hepatica calcium-binding protein with EF-hand and dynein light chain domains

FH22 has been previously identified as a calcium-binding protein from the common liver fluke, Fasciola hepatica. It is part of a family of at least four proteins in this organism which combine an EF-hand containing N-terminal domain with a C-terminal dynein light chain-like domain. Here we report further biochemical properties of FH22, which we propose should be renamed FhCaBP1 for consistency with other family members. Molecular modelling predicted that the two domains are linked by a flexible region and that the second EF-hand in the N-terminal domain is most likely the calcium ion binding site. Native gel electrophoresis demonstrated that the protein binds both calcium and manganese ions, but not cadmium, magnesium, strontium, barium, cobalt, copper(II), iron (II), nickel, zinc, lead or potassium ions. Calcium ion binding alters the conformation of the protein and increases its stability towards thermal denaturation. FhCaBP1 is a dimer in solution and calcium ions have no detectable effect on the protein's ability to dimerise. FhCaBP1 binds to the calmodulin antagonists trifluoperazine and chlorpromazine. Overall, the FhCaBP1's biochemical properties are most similar to FhCaBP2 a fact consistent with the close sequence and predicted structural similarity between the two proteins.

Similarity of a 16.5kDa tegumental protein of the human liver fluke Opisthorchis viverrini to nematode cytoplasmic motility protein

Opisthorchis viverrini is the causative agent of human opisthorchiasis in Thailand and long lasting infection with the parasite has been correlated with the development of cholangiocarcinoma. In this work we have molecularly characterized the first member of a protein family carrying two DM9 repeats in this parasite (OvDM9-1). InterPro and other protein family databases describe the DM9 repeat as a protein domain of unknown function that has been first noted in Drosophila melanogaster. Two paralogous proteins have been partially characterized in the genus Fasciola, Fasciola hepatica TP16.5, a novel tegumental antigen in human fascioliasis and, recently F. gigantica DM9-1, a parenchymal protein with structural similarity to nematode cytoplasmic motility protein (MFP2). In this study, we show further evidence that this family of trematode proteins is related to MFP2 in sequence and structure. Soluble recombinant OvDM9-1 was used for structural analyses and for production of specific antisera. The native protein was detected in soluble and insoluble crude worm extracts and in seemingly various oligomeric forms in the latter. The potential for oligomerization was supported by cross-linking experiments of recombinant OvDM9-1. Structure prediction suggested a β-rich secondary structure of the protein and this was supported by a circular dichroism analysis. Molecular modeling in Phyre2 identified both MFP2 domains as distant homologs of OvDM9-1. The protein was located in tegumental type tissue and the cecal epithelium in the mature parasite. Recombinant OvDM9-1 was used as target in indirect ELISA but sera from infected hamsters showed only marginal reactivity towards it. It is proposed that OvDM9-1 and other members of this protein family have a role in cellular transport through functions on the cytoskeleton.

FhCaBP2: a Fasciola hepatica calcium-binding protein with EF-hand and dynein light chain domains

FhCaBP2 is a Fasciola hepatica protein which belongs to a family of helminth calcium-binding proteins which combine an N-terminal domain containing two EF-hand motifs and a C-terminal dynein light chain-like (DLC-like) domain. Its predicted structure showed two globular domains joined by a flexible linker. Recombinant FhCaBP2 interacted reversibly with calcium and manganese ions, but not with magnesium, barium, strontium, copper (II), colbalt (II), iron (II), nickel, lead or potassium ions. Cadmium (II) ions appeared to bind non-site-specifically and destabilize the protein. Interaction with either calcium or magnesium ions results in a conformational change in which the protein's surface becomes more hydrophobic. The EF-hand domain alone was able to interact with calcium and manganese ions; the DLC-like domain was not. Alteration of a residue (Asp-58 to Ala) in the second EF-hand motif in this domain abolished ion-binding activity. This suggests that the second EF-hand is the one responsible for ion-binding. FhCaBP2 homodimerizes and the extent of dimerization was not affected by calcium ions or by the aspartate to alanine substitution in the second EF-hand. The isolated EF-hand and DLC-like domains are both capable of homodimerization. FhCaBP2 interacted with the calmodulin antagonists trifluoperazine, chlorpromazine, thiamylal and W7. Interestingly, while chlorpromazine and thiamylal interacted with the EF-hand domain (as expected), trifluoperazine and W7 bound to the DLC-like domain. Overall, FhCaBP2 has distinct biochemical properties compared with other members of this protein family from Fasciola hepatica, a fact which supports the hypothesis that these proteins have different physiological roles.

Comparative biochemical analysis of three members of the Schistosoma mansoni TAL family: Differences in ion and drug binding properties

The tegumental allergen-like (TAL) proteins from Schistosoma mansoni are part of a family of calcium binding proteins found only in parasitic flatworms. These proteins have attracted interest as potential drug or vaccine targets, yet comparatively little is known about their biochemistry. Here, we compared the biochemical properties of three members of this family: SmTAL1 (Sm22.6), SmTAL2 (Sm21.7) and SmTAL3 (Sm20.8). Molecular modelling suggested that, despite similarities in domain organisation, there are differences in the three proteins' structures. SmTAL1 was predicted to have two functional calcium binding sites and SmTAL2 was predicted to have one. Despite the presence of two EF-hand-like structures in SmTAL3, neither was predicted to be functional. These predictions were confirmed by native gel electrophoresis, intrinsic fluorescence and differential scanning fluorimetry: both SmTAL1 and SmTAL2 are able to bind calcium ions reversibly, but SmTAL3 is not. SmTAL1 is also able to interact with manganese, strontium, iron(II) and nickel ions. SmTAL2 has a different ion binding profile interacting with cadmium, manganese, magnesium, strontium and barium ions in addition to calcium. All three proteins form dimers and, in contrast to some Fasciola hepatica proteins from the same family; dimerization is not affected by calcium ions. SmTAL1 interacts with the anti-schistosomal drug praziquantel and the calmodulin antagonists trifluoperazine, chlorpromazine and W7. SmTAL2 interacts only with W7. SmTAL3 interacts with the aforementioned calmodulin antagonists and thiamylal, but not praziquantel. Overall, these data suggest that the proteins have different biochemical properties and thus, most likely, different in vivo functions.

An EF-handed Ca(2+)-binding protein of Chinese liver fluke Clonorchis sinensis

A cDNA clone encoding 8 kDa protein was retrieved from an EST pool of Chinese liver fluke Clonorchis sinensis. A deduced polypeptide of the cDNA clone was similar to 8 kDa Ca(2+)-binding proteins from other parasitic trematodes, and, thus, named as CsCa8, containing two EF-hand Ca(2+)-binding sites. Homology models predicted CsCa8 to be a single globular structure having four helices and molecular folds similar to Ca(2+)-binding state of other small Ca(2+)-binding proteins. Recombinant CsCa8 protein showed specific Ca(2+)-binding affinity and shifting in native gel mobility assay. Mouse immune sera raised against recombinant CsCa8 protein recognized native CsCa8 from adult C. sinensis worm extract. CsCa8 was localized in oral and ventral suckers, vitelline follicles and subtegumental tissues. These findings suggest that CsCa8 might be involved in cellular Ca(2+) signal transduction for muscle contraction and egg production.

Citrate synthase from the liver fluke Fasciola hepatica

Citrate synthase catalyses the first step of the Krebs' tricarboxylic acid cycle. A sequence encoding citrate synthase from the common liver fluke, Fasciola hepatica, has been cloned. The encoded protein sequence is predicted to fold into a largely α-helical protein with high structural similarity to mammalian citrate synthases. Although a hexahistidine-tagged version of the protein could be expressed in Escherichia coli, it was not possible to purify it by nickel-affinity chromatography. Similar results were obtained with a version of the protein which lacks the putative mitochondrial targeting sequence (residues 1 to 29). However, extracts from bacterial cells expressing this version had additional citrate synthase activity after correcting for the endogenous, bacterial activity. The apparent K m for oxaloacetate was found to be 0.22 mM, which is higher than that observed in mammalian citrate synthases. Overall, the sequence and structure of F. hepatica citrate synthase are similar to ones from other eukaryotes, but there are enzymological differences which merit further investigation.

FhCaBP3: a Fasciola hepatica calcium binding protein with EF-hand and dynein light chain domains

A DNA sequence encoding a protein with predicted EF-hand and dynein light chain binding domains was identified in a Fasciola hepatica EST library. Sequence analysis of the encoded protein revealed that the most similar known protein was the Fasciola gigantica protein FgCaBP3 and so this newly identified protein was named FhCaBP3. Molecular modelling of FhCaBP3 predicted a highly flexible N-terminal region, followed by a domain containing two EF-hand motifs the second of which is likely to be a functioning divalent ion binding site. The C-terminal domain of the protein contains a dynein light chain like region. Interestingly, molecular modelling predicts that calcium ion binding to the N-terminal domain destabilises the β-sheet structure of the C-terminal domain. FhCaBP3 can be expressed in, and purified from, Escherichia coli. The recombinant protein dimerises and the absence of calcium ions appeared to promote dimerisation. Native gel shift assays demonstrated that the protein bound to calcium and manganese ions, but not to magnesium, barium, zinc, strontium, nickel, copper or cadmium ions. FhCaBP3 interacted with the calmodulin antagonists trifluoperazine, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide and chlorpromazine as well as the myosin regulatory light chain-binding drug praziquantel. Despite sequence and structural similarities to other members of the same protein family from F. hepatica, FhCaBP3 has different biochemical properties to the other well characterised family members, FH22 and FhCaBP4. This suggests that each member of this trematode calcium-binding family has discrete functional roles within the organism.