Characterization and cloning of metallo-proteinase in the excretory/secretory products of the infective-stage larva of Trichinella spiralis

Salmon louse labial gland enzymes: implications for host settlement and immune modulation

Salmon louse (Lepeophtheirus salmonis) is a skin- and blood-feeding ectoparasite, infesting salmonids. While feeding, labial gland proteins from the salmon louse may be deposited on the Atlantic salmon (Salmo salar) skin. Previously characterized labial gland proteins are involved in anti-coagulation and may contribute to inhibiting Atlantic salmon from mounting a sufficient immune response against the ectoparasite. As labial gland proteins seem to be important in the host-parasite interaction, we have, therefore, identified and characterized ten enzymes localized to the labial gland. They are a large group of astacins named L. salmonis labial gland astacin 1-8 (LsLGA 1-8), one serine protease named L. salmonis labial gland serine protease 1 (LsLGSP1), and one apyrase named L. salmonis labial gland apyrase 1 (LsLGAp1). Protein domain predictions showed that LsLGA proteins all have N-terminal ShK domains, which may bind to potassium channels targeting the astacins to its substrate. LsLGA1 and -4 are, in addition, expressed in another gland type, whose secrete also meets the host-parasite interface. This suggests that LsLGA proteins may have an anti-microbial function and may prevent secondary infections in the wounds. LsLGAp1 is predicted to hydrolyze ATP or AMP and is, thereby, suggested to have an immune dampening function. In a knockdown study targeting LsLGSP1, a significant increase in IL-8 and MMP13 at the skin infestation site was seen under LsLGSP1 knockdown salmon louse compared to the control, suggesting that LsLGSP1 may have an anti-inflammatory effect. Moreover, most of the identified labial gland proteins are expressed in mature copepodids prior to host settlement, are not regulated by starvation, and are expressed at similar or higher levels in lice infesting the salmon louse-resistant pink salmon (Oncorhynchus gorbuscha). This study, thereby, emphasizes the importance of labial gland proteins for host settlement and their immune dampening function. This work can further contribute to anti-salmon louse treatment such as vaccine development, functional feed, or gene-edited salmon louse-resistant Atlantic salmon.

Structural and evolutionary insights into astacin metallopeptidases

The astacins are a family of metallopeptidases (MPs) that has been extensively described from animals. They are multidomain extracellular proteins, which have a conserved core architecture encompassing a signal peptide for secretion, a prodomain or prosegment and a zinc-dependent catalytic domain (CD). This constellation is found in the archetypal name-giving digestive enzyme astacin from the European crayfish Astacus astacus. Astacin catalytic domains span ∼200 residues and consist of two subdomains that flank an extended active-site cleft. They share several structural elements including a long zinc-binding consensus sequence (HEXXHXXGXXH) immediately followed by an EXXRXDRD motif, which features a family-specific glutamate. In addition, a downstream SIMHY-motif encompasses a "Met-turn" methionine and a zinc-binding tyrosine. The overall architecture and some structural features of astacin catalytic domains match those of other more distantly related MPs, which together constitute the metzincin clan of metallopeptidases. We further analysed the structures of PRO-, MAM, TRAF, CUB and EGF-like domains, and described their essential molecular determinants. In addition, we investigated the distribution of astacins across kingdoms and their phylogenetic origin. Through extensive sequence searches we found astacin CDs in > 25,000 sequences down the tree of life from humans beyond Metazoa, including Choanoflagellata, Filasterea and Ichtyosporea. We also found < 400 sequences scattered across non-holozoan eukaryotes including some fungi and one virus, as well as in selected taxa of archaea and bacteria that are pathogens or colonizers of animal hosts, but not in plants. Overall, we propose that astacins originate in the root of Holozoa consistent with Darwinian descent and that the latter genes might be the result of horizontal gene transfer from holozoan donors.

Proteomic analysis of hydrolytic proteases in excretory/secretory proteins from Trichinella spiralis intestinal infective larvae using zymography combined with shotgun LC-MS/MS approach

The critical step of Trichinella spiralis infection is that the muscle larvae (ML) are activated to intestinal infective larvae (IIL) which invade the intestinal columnar epithelium to further develop. The IIL excretory/secretory (ES) proteins play an important role in host-parasite interaction. Proteolytic enzymes are able to mediate the tissue invasion, thereby increasing the susceptibility of parasites to their hosts. The aim of the current study was to screen and identify the natural active proteases in T. spiralis IIL ES proteins using Western blot and gel zymography combined with liquid chromatography tandem mass spectrometry (LC-MS/MS). The T. spiralis ML and IIL ES proteins were collected from the in vitro cultures and their enzymatic acitvities were examined by gelatin zymography and azocasein degradation. The protease activities were partially inhibited by PMSF, E-64 and EDTA. Three protein bands (45, 118 and 165 kDa) of T. spiralis IIL ES proteins were identified by shotgun LC-MS/MS because they have hydrolytic activity to gelatin compared to the ML ES proteins. Total of 30 T. spiralis proteins were identified and they are mainly serine proteinases (19), but also metalloproteinases (7) and cysteine proteinases (3). The qPCR results indicated that transcription levels of four T. spiralis protease genes (two serine proteases, a cathepsin B-like cysteine proteinase and a zinc metalloproteinase) at IIL stage were obviously higher than at the ML stage. These proteolytic enzymes are directly exposed to the host intestinal milieu and they may mediate the worm invasion of enteral epithelium and escaping from the host's immune responses. The results provide the new insights into understanding of the interaction of T. spiralis with host and the invasion mechanism.

Identification of proteins from the secretory/excretory products (SEPs) of the branchiuran ectoparasite Argulus foliaceus (Linnaeus, 1758) reveals unique secreted proteins amongst haematophagous ecdysozoa

BACKGROUND

It is hypothesised that being a blood-feeding ectoparasite, Argulus foliaceus (Linnaeus, 1758), uses similar mechanisms for digestion and host immune evasion to those used by other haematophagous ecdysozoa, including caligid copepods (e.g. sea louse). We recently described and characterised glands associated with the feeding appendages of A. foliaceus using histological techniques. The work described in the present study is the first undertaken with the objective of identifying and partially characterising the components secreted from these glands using a proteomic approach.

METHODS

Argulus foliaceus parasites were sampled from the skin of rainbow trout (Oncorhynchus mykiss), from Loch Fad on the Isle of Bute, Scotland, UK. The proteins from A. foliaceus secretory/excretory products (SEPs) were collected from the supernatant of artificial freshwater conditioned with active adult parasites (n = 5-9 per ml; n = 560 total). Proteins within the SEPs were identified and characterised using LC-ESI-MS/MS analysis. Data are available via ProteomeXchange with identifier PXD016226.

RESULTS

Data mining of a protein database translated from an A. foliaceus dataset using ProteinScape allowed identification of 27 predicted protein sequences from the A. foliaceus SEPs, each protein matching the criteria of 2 peptides with at least 4 contiguous amino acids. Nine proteins had no matching sequence through OmicsBox (Blast2GO) analysis searches suggesting that Argulus spp. may additionally have unique proteins present in their SEPs. SignalP 5.0 software, identified 13 proteins with a signal sequence suggestive of signal peptides and supportive of secreted proteins being identified. Notably, the functional characteristics of identified A. foliaceus proteins/domains have also been described from the salivary glands and saliva of other blood-feeding arthropods such as ticks. Identified proteins included: transporters, peroxidases, metalloproteases, proteases and serine protease inhibitors which are known to play roles in parasite immune evasion/induction (e.g. astacin), immunomodulation (e.g. serpin) and digestion (e.g. trypsin).

CONCLUSIONS

To our knowledge, the present study represents the first proteomic analysis undertaken for SEPs from any branchiuran fish louse. Here we reveal possible functional roles of A. foliaceus SEPs in digestion and immunomodulation, with a number of protein families shared with other haematophagous ectoparasites. A number of apparently unique secreted proteins were identified compared to other haematophagous ecdysozoa.

Genomic and phylogenetic analysis of choriolysins, and biological activity of hatching liquid in the flatfish Senegalese sole

The hatching enzymes or choriolysins are key proteases in fish life cycle controlling the release of larvae to surrounding environment that have been suggested as target for novel biotechnological uses. Due to the large amounts of eggs released by the flatfish Solea senegalensis, during the spawning season, the hatching liquid properties and choriolysin-encoding genes were investigated in this species. A genomic analysis identified four putative genes referred to as SseHCEa, SseHCEb, SseLCE and SseHE. The phylogenetic analysis classified these paralogs into two clades, the clade I containing SseHCE paralogs and the clade II containing two well-supported subclades named as HE and LCE. The two SseHCE paralogs were intron-less and both genes were tandemly arrayed very close in the genome. The synteny and gene rearrangement identified in the flatfish lineage indicated that the duplication of these two paralogs occurred recently and they are under divergent evolution. The genes SseHE and SseLCE were structured in 8 exons and 7 introns and the synteny was conserved in teleosts. Expression studies confirmed that the four genes were expressed in the hatching gland cells and they migrate co-ordinately from the head to around the yolk sac close to the hatch with specific temporal and intensity expression profiles. Although the mRNA levels of the four genes peaked in the hours previous to larval hatching, the SseHCE and SseLCE paralogs kept a longer expression than SseHE after hatching. These expression patterns were consistent even when larvae were incubated at different temperatures that modified hatching times. The analysis of hatching-liquid using SDS-PAGE and zymography analyses of hatching liquid identified a major band of expected choriolysin size. The optimal pH for protease activity was 8.5 and inhibition assays using EDTA demonstrated that most of the activity in the hatching liquid was due to metalloproteases with Ca²⁺ ions acting as the most effective metal to restore the activity. All these data provide new clues about the choriolysin evolution and function in flatfish with impact in the aquaculture and the blue cosmetic industry.

Trichinella spiralis muscle larvae excretory-secretory products induce changes in cytoskeletal and myogenic transcription factors in primary myoblast cultures

Trichinella spiralis infection in skeletal muscle culminates with nurse cell formation. The participation of excretory-secretory products of the muscle larvae has been implicated in this process through different studies performed in infected muscle and the muscle cell line C2C12. In this work, we developed primary myoblast cultures to analyse the changes induced by excretory-secretory products of the muscle larvae in muscle cells. Microarray analyses revealed expression changes in muscle cell differentiation, proliferation, cytoskeleton organisation, cell motion, transcription, cell cycle, apoptosis and signalling pathways such as MAPK, Jak-STAT, Wnt and PI3K-Akt. Some of these changes were further evaluated by other methodologies such as quantitative real-time PCR (qRT-PCR) and western blot, confirming that excretory-secretory products of the muscle larvae treated primary mouse myoblasts undergo increased proliferation, decreased expression of MHC and up-regulation of α-actin. In addition, changes in relevant muscle transcription factors (Pax7, Myf5 and Mef2c) were observed. Taken together, these results provide new information about how T. spiralis could alter the normal process of skeletal muscle repair after ML invasion to accomplish nurse cell formation.

Identification, Characterization, and Structure of Tm16 from Trichuris muris

Trichuriasis is a disease of poverty for which excretory and secretory (ES) products that induce the protective immunity are being investigated as candidate vaccines antigens. In this study, ES products of T. muris and immune sera were produced. The immune sera recognized more than 20 proteins on a 2D-gel of ES products of T. muris adult worms. Tm16 was one of the proteins identified by mass spectrometry. Tm16 shares 57% sequence identity with Ov16, an immunodominant diagnostic antigen from Onchocerca volvulus. Recombinant Tm16 with a carboxyl terminal hexahistidine was produced using Pichia pastoris. Polyclonal antibodies against rTm16 were generated by one-prime and two-boost immunization of three female Balb/c mice with 25 μg of recombinant Tm16 emulsified with ISA720 adjuvant. These polyclonal antibodies confirmed that Tm16 is localized to the ES products and the soluble fraction of the adult worm. Additionally, the high-resolution crystal structure of Tm16 was solved by molecular replacement. Tm16 belongs to the phosphatidylethanolamine-binding-like protein (PEBP1) family and this is the first structure of a PEBP1 from a parasite.

The genomic basis of parasitism in the Strongyloides clade of nematodes

Soil-transmitted nematodes, including the Strongyloides genus, cause one of the most prevalent neglected tropical diseases. Here we compare the genomes of four Strongyloides species, including the human pathogen Strongyloides stercoralis, and their close relatives that are facultatively parasitic (Parastrongyloides trichosuri) and free-living (Rhabditophanes sp. KR3021). A significant paralogous expansion of key gene families--families encoding astacin-like and SCP/TAPS proteins--is associated with the evolution of parasitism in this clade. Exploiting the unique Strongyloides life cycle, we compare the transcriptomes of the parasitic and free-living stages and find that these same gene families are upregulated in the parasitic stages, underscoring their role in nematode parasitism.

Onchocerca volvulus Molting Inhibitors Identified through Scaffold Hopping

The anthelmintic closantel has shown promise in abrogating the L3 molting of Onchocerca volvulus, the causative agent of the infectious disease onchocerciasis. In our search for alternative scaffolds, we utilized a fragment replacement/modification approach to generate novel chemotypes with improved chitinase inhibitory properties. Further evaluation of the compounds unveiled the potential of urea-tropolones as potent inhibitors of O. volvulus L3 molting.

Enzymology of the nematode cuticle: A potential drug target?

All nematodes possess an external structure known as the cuticle, which is crucial for their development and survival. This structure is composed primarily of collagen, which is secreted from the underlying hypodermal cells. Extensive studies using the free-living nematode Caenorhabditis elegans demonstrate that formation of the cuticle requires the activity of an extensive range of enzymes. Enzymes are required both pre-secretion, for synthesis of component proteins such as collagen, and post-secretion, for removal of the previous developmental stage cuticle, in a process known as moulting or exsheathment. The excretion/secretion products of numerous parasitic nematodes contain metallo-, serine and cysteine proteases, and these proteases are conserved across the nematode phylum and many are involved in the moulting/exsheathment process. This review highlights the enzymes required for cuticle formation, with a focus on the post-secretion moulting events. Where orthologues of the C. elegans enzymes have been identified in parasitic nematodes these may represent novel candidate targets for future drug/vaccine development.

Proteolytic activity in the adult and larval stages of the human roundworm parasite Angiostrongylus costaricensis

Angiostrongylus costaricensis is a nematode that causes abdominal angiostrongyliasis, a widespread human parasitism in Latin America. This study aimed to characterize the protease profiles of different developmental stages of this helminth. First-stage larvae (L1) were obtained from the faeces of infected Sigmodon hispidus rodents and third-stage larvae (L3) were collected from mollusks Biomphalaria glabrata previously infected with L1. Adult worms were recovered from rodent mesenteric arteries. Protein extraction was performed after repeated freeze-thaw cycles followed by maceration of the nematodes in 40 mM Tris base. Proteolysis of gelatin was observed by zymography and found only in the larval stages. In L3, the gelatinolytic activity was effectively inhibited by orthophenanthroline, indicating the involvement of metalloproteases. The mechanistic class of the gelatinases from L1 could not be precisely determined using traditional class-specific inhibitors. Adult worm extracts were able to hydrolyze haemoglobin in solution, although no activity was observed by zymography. This haemoglobinolytic activity was ascribed to aspartic proteases following its effective inhibition by pepstatin, which also inhibited the haemoglobinolytic activity of L1 and L3 extracts. The characterization of protease expression throughout the A. costaricensis life cycle may reveal key factors influencing the process of parasitic infection and thus foster our understanding of the disease pathogenesis.

Transcriptomic analysis of four developmental stages of Strongyloides venezuelensis

Strongyloides venezuelensis is one of some 50 species of genus Strongyloides, obligate gastrointestinal parasites of vertebrates, responsible for strongyloidiasis in humans and other domestic/companion animals. Although S. venezuelensis has been widely used as a model species for studying human/animal strongyloidiasis, the sequence information for this species has been quite limited. To create a more comprehensive catalogue of expressed genes for identification of genes potentially involved in animal parasitism, we conducted a de novo sequencing analysis of the transcriptomes from four developmental stages of S. venezuelensis, using a Roche 454 GS FLX Titanium pyrosequencing platform. A total of 14,573 contigs were produced after de novo assemblies of over 2 million sequencing reads and formed a dataset "Vene454". BLAST homology search of Vene454 against proteome and transcriptome data from other animal-parasitic and non-animal-parasitic nematode species revealed several interesting genes, which may be potentially related to animal parasitism, including nicotinamide phosphoribosyltransferase and ferrochelatase. The Vene454 dataset analysis also enabled us to identify transcripts that are specifically enriched in each developmental stage. This work represents the first large-scale transcriptome analysis of S. venezuelensis and the first study to examine the transcriptome of the lung L3 developmental stage of any Strongyloides species. The results not only will serve as valuable resources for future functional genomics analyses to understand the molecular aspects of animal parasitism, but also will provide essential information for ongoing whole genome sequencing efforts in this species.

In silico secretome analysis approach for next generation sequencing transcriptomic data

BACKGROUND

Excretory/secretory proteins (ESPs) play a major role in parasitic infection as they are present at the host-parasite interface and regulate host immune system. In case of parasitic helminths, transcriptomics has been used extensively to understand the molecular basis of parasitism and for developing novel therapeutic strategies against parasitic infections. However, none of transcriptomic studies have extensively covered ES protein prediction for identifying novel therapeutic targets, especially as parasites adopt non-classical secretion pathways.

RESULTS

We developed a semi-automated computational approach for prediction and annotation of ES proteins using transcriptomic data from next generation sequencing platforms. For the prediction of non-classically secreted proteins, we have used an improved computational strategy, together with homology matching to a dataset of experimentally determined parasitic helminth ES proteins. We applied this protocol to analyse 454 short reads of parasitic nematode, Strongyloides ratti. From 296231 reads, we derived 28901 contigs, which were translated into 20877 proteins. Based on our improved ES protein prediction pipeline, we identified 2572 ES proteins, of which 407 (1.9%) proteins have classical N-terminal signal peptides, 923 (4.4%) were computationally identified as non-classically secreted while 1516 (7.26%) were identified by homology to experimentally identified parasitic helminth ES proteins. Out of 2572 ES proteins, 2310 (89.8%) ES proteins had homologues in the free-living nematode Caenorhabditis elegans and 2220 (86.3%) in parasitic nematodes. We could functionally annotate 1591 (61.8%) ES proteins with protein families and domains and establish pathway associations for 691 (26.8%) proteins. In addition, we have identified 19 representative ES proteins, which have no homologues in the host organism but homologous to lethal RNAi phenotypes in C. elegans, as potential therapeutic targets.

CONCLUSION

We report a comprehensive approach using freely available computational tools for the secretome analysis of NGS data. This approach has been applied to S. ratti 454 transcriptomic data for in silico excretory/secretory proteins prediction and analysis, providing a foundation for developing new therapeutic solutions for parasitic infections.

Developmental transcriptomic features of the carcinogenic liver fluke, Clonorchis sinensis

Clonorchis sinensis is the causative agent of the life-threatening disease endemic to China, Korea, and Vietnam. It is estimated that about 15 million people are infected with this fluke. C. sinensis provokes inflammation, epithelial hyperplasia, and periductal fibrosis in bile ducts, and may cause cholangiocarcinoma in chronically infected individuals. Accumulation of a large amount of biological information about the adult stage of this liver fluke in recent years has advanced our understanding of the pathological interplay between this parasite and its hosts. However, no developmental gene expression profiles of C. sinensis have been published. In this study, we generated gene expression profiles of three developmental stages of C. sinensis by analyzing expressed sequence tags (ESTs). Complementary DNA libraries were constructed from the adult, metacercaria, and egg developmental stages of C. sinensis. A total of 52,745 ESTs were generated and assembled into 12,830 C. sinensis assembled EST sequences, and then these assemblies were further categorized into groups according to biological functions and developmental stages. Most of the genes that were differentially expressed in the different stages were consistent with the biological and physical features of the particular developmental stage; high energy metabolism, motility and reproduction genes were differentially expressed in adults, minimal metabolism and final host adaptation genes were differentially expressed in metacercariae, and embryonic genes were differentially expressed in eggs. The higher expression of glucose transporters, proteases, and antioxidant enzymes in the adults accounts for active uptake of nutrients and defense against host immune attacks. The types of ion channels present in C. sinensis are consistent with its parasitic nature and phylogenetic placement in the tree of life. We anticipate that the transcriptomic information on essential regulators of development, bile chemotaxis, and physico-metabolic pathways in C. sinensis that presented in this study will guide further studies to identify novel drug targets and diagnostic antigens.

Comparison of the surface coat proteins of the pine wood nematode appeared during host pine infection and in vitro culture by a proteomic approach

Pine wilt disease, caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, has become of worldwide quarantine concern in recent years. Here, we disclosed the surface coat (SC) proteins of the PWN which are thought to be one of the key components in pine wilt development. This is the first report that focused on the SC proteins and thoroughly identified those proteins of a plant-parasitic nematode using the proteomic approach. In this study, SC protein profiles were compared for PWNs grown on the fungus Botrytis cinerea and in host pine seedlings. The results demonstrated that the gross amount of PWN SC proteins drastically increased during infection of the host pine. Thirty-seven protein bands showed significant quantity differences between fungus-grown and host-origin PWNs, and were used for identification by matrix-assisted laser desorption ionization time of flight mass spectrometry analysis. These included several proteins that are presumed to be involved in the host immune response; for example, regulators of reactive oxygen species (ROS) and a ROS scavenger. These results might suggest that the PWN SC proteins are crucial in modulating or evading host immune response. Our data provide a new insight into the mechanism of pine wilt disease and the biological role of the SC proteins of plant-parasitic nematodes.

Proteomic analysis of excretory/secretory products released by Teladorsagia circumcincta larvae early post-infection

Teladorsagia circumcincta is an important parasitic nematode of domestic small ruminants. Drug resistance in this species is common so alternative methods of control are required. As animals develop immunity to T. circumcincta, vaccination is a valid option. Little is known about the antigens that play a role in stimulating immunity at this host/parasite interface. As responses generated between 1 and 5 dpi are known to affect development of these nematodes in their gastric niche, we focused on proteins released during the early stages of infection. To identify molecules potentially involved in immunity, we undertook a proteomics analysis of proteins released from larvae harvested at 1-, 3- and 5-days post-infection (dpi). This analysis produced peptide sequence data that was used to search information available in T. circumcincta expressed sequence tag (EST) databases and enabled identification of a number of excretory/secretory (ES) proteins. Immunoblots were performed to assess the relative molecular weight of ES antigens that were targets of local IgA responses in mucus from sheep rendered immune to infection. ELISA was performed to assess antigen-specific mucus IgA levels in individual sheep. These experiments provided preliminary evidence that the proteins identified in the larval secretome were subject to these antibody responses.

Signal sequence analysis of protein sequences from the filarial nematode parasite Brugia malayi and the evolution of secreted proteins in parasites

Taking a genomic approach to characterize potential secreted products, we analyzed putative protein sequences from Brugia malayi whole-genome shotgun sequencing project. SignalP analysis was applied to predict protein sequences and to identify potential signal peptides and anchors. We randomly analyzed 552 sequences, of which 88 (15.9%) bear predicted signal sequence coding regions. Through comparisons of sequences with homologs from other species, we found that although some of the sequences with signal sequences have no homologs with others, there are almost the same amounts of the sequences with signals which are highly conserved. Considering the distribution of secretory proteins of B. malayi in three categories has not made big differences, and most of the homologues of free-living nematodes of these secretory proteins also contained either N-signal signal peptides or signal anchors; we speculated that secretory proteins may be in the same evolutional status as the non-secretory proteins.

Functional genes and proteins of Trichinella spp

Research of Trichinella proteins has been conducted with emphasis on excretory-secretory (E-S) products of muscle larvae because of two reasons. The first is that it has prominent and narrow specific antigenicity, and the second is that it may play some role in nurse cell formation after being secreted into host muscle cells. Proteomic analysis of E-S proteins was further advanced by the aid of new analytical methods such as gene cloning, matrix-assisted laser desorption-ionization time-of-flight mass spectrometry, and expressed sequence tags database analysis. As the research progressed, the interest of researchers moved to identification of function of E-S products, which has shed further light on the intriguing relationships between parasites and hosts. Major constituents of the E-S products include 43-, 53-, and 45-kDa glycoprotein derived from the stichosome. Many proteins were discovered in E-S products after the 43-, 53-, and 45-kDa proteins although the relationships among them remain unclear. Some of the new proteins were partially defined in terms of their function including nuclear antigens, MyoD-like protein, TsJ5 protein, etc. There are better-characterized proteins based on the gene molecular method, which allow easier identification of the function of proteins of interest. Such examples were demonstrated by proteinases, proteinase inhibitors, heat shock proteins, glycosidases, etc.

Characterisation of novel protein families secreted by muscle stage larvae of Trichinella spiralis

Proteins secreted by Trichinella spiralis have a potential role in remodelling host skeletal muscle. However, whilst many parasite-secreted proteins have been identified, it has rarely been demonstrated that these are secreted into the nurse cell. Using an informatics-based analysis, we have searched the T. spiralis expressed sequence tag (EST) datasets for cDNAs encoding potential secreted proteins. Here we describe the characterisation of three of the top candidates isolated from our analysis, termed secreted from muscle stage larvae (SML)-1, -2 and -3. All three proteins were demonstrated to be secreted by muscle stage larvae, and immunohistochemical analysis established that SML-1 and -2 are secreted into developing nurse cells. We also show that SML-2 is processed from a precursor into smaller peptides by a metalloprotease contained within T. spiralis-secreted products. With the identification of these and other secreted proteins, we now have molecules to test in functional assays designed to dissect molecular features of the developing nurse cell.

Meprins, membrane-bound and secreted astacin metalloproteinases

The astacins are a subfamily of the metzincin superfamily of metalloproteinases. The first to be characterized was the crayfish enzyme astacin. To date more than 200 members of this family have been identified in species ranging from bacteria to humans. Astacins are involved in developmental morphogenesis, matrix assembly, tissue differentiation and digestion. Family members include the procollagen C-proteinase (BMP1, bone morphogenetic protein 1), tolloid and mammalian tolloid-like, HMP (Hydra vulgaris metalloproteinase), sea urchin BP10 (blastula protein) and SPAN (Strongylocentrotus purpuratus astacin), the 'hatching' subfamily comprising alveolin, ovastacin, LCE, HCE ('low' and 'high' choriolytic enzymes), nephrosin (from carp head kidney), UVS.2 from frog, and the meprins. In the human and mouse genomes, there are six astacin family genes (two meprins, three BMP1/tolloid-like, one ovastacin), but in Caenorhabditis elegans there are 40. Meprins are the only astacin proteinases that function on the membrane and extracellularly by virtue of the fact that they can be membrane-bound or secreted. They are unique in their domain structure and covalent subunit dimerization, oligomerization propensities, and expression patterns. They are normally highly regulated at the transcriptional and post-translational levels, localize to specific membranes or extracellular spaces, and can hydrolyse biologically active peptides, cytokines, extracellular matrix (ECM) proteins and cell-surface proteins. The in vivo substrates of meprins are unknown, but the abundant expression of these proteinases in the epithelial cells of the intestine, kidney and skin provide clues to their functions.

Stage-specific gene expression in Teladorsagia circumcincta (Nematoda: Strongylida) infective larvae and early parasitic stages

Suppression subtractive hybridisation was used to enrich genes expressed in a stage-specific manner in infective, exsheathed L3s (xL3) versus early L4s of the ovine nematode, Teladorsagia circumcincta prior to gene expression profiling by microarray. The 769 cDNA sequences obtained from the xL3-enriched library contained 361 unique sequences, with 292 expressed sequence tags (ESTs) being represented once ("singletons") and 69 sequences which were represented more than once (overlapping and non-overlapping "contigs"). The L4-enriched EST dataset contained 472 unique sequences, with 314 singletons and 158 contigs. Of these 833 sequences, 85% of the xL3 sequences and 86% of the L4 sequences exhibited homology to known genes or ESTs derived from other species of nematode. Quantitative differential expression (P<0.05) was demonstrated for 563 (68%) of the ESTs by microarray. Within the L3-specific dataset, more than 30% of the transcripts represented the enzyme, guanosine-5'-triphosphate (GTP)-cyclohydrolase, which is the first and rate-limiting enzyme of the tetrahydrobiopterin synthesis pathway and may be involved in critical elements of larval development. In L4s, proteolytic enzymes were highly up-regulated, as were collagens and a number of previously characterised secretory proteins, reflecting the rapid growth of these larvae in abomasal glands. Nucleotide sequence data reported in this paper are available in the EMBL, GenBank and DDJB databases under accession numbers AM 743198-AM 744942.

Identification and characterization of onchoastacin, an astacin-like metalloproteinase from the filaria Onchocerca volvulus

The tissue-invasive nematode Onchocerca volvulus causes skin and eye pathology in human onchocerciasis. While the adult females reside sessile in subcutaneous nodules, the microfilariae are abundantly released from the nodules, males and juvenile worms migrate through the host tissue. Matrix-degrading metallo- and serine proteinases have been detected in excretory-secretory worm products that may be essential for migration of the mobile stages. In this study, a 1713bp long cDNA encoding for a putative proteinase of O. volvulus has been isolated. The predicted protein sequence includes a signal peptide indicating secretion to the extracellular space, a propeptide, an astacin-like protease domain, an EGF-like and a CUB-domain, thereby identifying the protein as a member of the astacin family of zinc endopeptidases. Onchoastacin, Ov-AST-1, is most closely related to a subfamily comprising nematode astacins including Caenorhabditis and Ancylostoma. Ov-AST-1 was expressed as a recombinant protein in baculovirus-infected insect cells and exhibited enzymatic activity. The exposure of onchoastacin to the host immune system is indicated by demonstration of IgG reacting with the recombinant Ov-AST-1 and with two peptides of the protein. Since a homologous metalloproteinase is part of a promising hookworm vaccine, Ov-AST-1 may be a candidate for intervention strategies in filarial infections.

Proteomic analysis of the excretory-secretory proteins of the Trichinella spiralis L1 larva, a nematode parasite of skeletal muscle

Trichinella spiralis is an intracellular nematode parasite of mammalian skeletal muscle. Infection of the muscle cell leads to the formation of a host-parasite complex that results in profound alterations to the host cell and a re-alignment of muscle-specific gene expression. The role of parasite excretory-secretory (ES) proteins in mediating these effects is currently unknown, largely due to the difficulty in identifying and assigning function to individual proteins. In this study, a global proteomics approach was used to analyse the ES proteins from T. spiralis muscle larvae. Following 2-DE of ES proteins,MALDI-TOF-MS and LC-MS/MS were used to identify the peptide spots. Specific Trichinella EST databases were assembled and used to analyse the data. Despite the current absence of a Trichinella genome-sequencing project, 43 out of 52 protein spots analysed were identified and included the major secreted glycoproteins. Other novel proteins were identified from matches with sequences in the T. spiralis database. Our results demonstrate the value of proteomics as a tool for the identification of Trichinella ES proteins and in the study of the molecular mechanism underpinning the formation of the host-parasite complex during Trichinella infections.

Cloning and analysis of a cDNA encoding a putative serine protease comprising two trypsin-like domains of Trichinella spiralis

The cDNA encoding a putative serine protease, TsSerP, was cloned by degenerative polymerase chain reaction and screening of the cDNA library from Trichinella spiralis adult-newborn larvae stage. Sequence analysis revealed the presence of two trypsin-like serine protease domains flanking a hydrophilic domain, with the catalytic triad residue histidine in the alpha domain substituted by an arginine residue. Southern blots indicated that this was a single copy gene in the parasite genome. Northern blots demonstrated a single 2.3-kb transcript during the muscle larvae and adult stages of T. spiralis. The recombinant protein from the TsSerP beta domain (betaSerP) was produced but not recognised by T. spiralis-infected swine serum. An anti-betaSerP polyclonal serum detected a 69-kDa polypeptide in the soluble antigens of T. spiralis muscle larvae. Immunolocalisation analysis located TsSerP on the inner layer of the cuticle and oesophagus of the parasite, suggesting a potential role in its moulting and/or digestive functions.

Profiling excretory/secretory proteins of Trichinella spiralis muscle larvae by two-dimensional gel electrophoresis and mass spectrometry

Infection of mammalian skeletal muscle with the intracellular parasite Trichinella spiralis results in profound alterations in the host cell and a realignment of host cell gene expression. The role of parasite excretory/secretory (E/S) products in mediating these effects is unknown, largely due to the difficulty in identifying and assigning function to individual proteins. In this study, we have used two-dimensional electrophoresis to analyse the profile of muscle larva excreted/secreted proteins and have coupled this to protein identification using MALDI-TOF mass spectrometry. Interpretation of the peptide mass fingerprint data has relied primarily on the interrogation of a custom-made Trichinella EST database and the NemaGene cluster database for T. spiralis. Our results suggest that this proteomic approach is a useful tool to study protein expression in Trichinella spp. and will contribute to the identification of excreted/secreted proteins.

Gene discovery in the adenophorean nematode Trichinella spiralis: an analysis of transcription from three life cycle stages

Expressed sequence tags (ESTs) were produced from cDNA libraries for immature L1, mature muscle larva and adult stages of the adenophorean nematode Trichinella spiralis. 10,130 ESTs were grouped into 3454 gene clusters. The clusters represent a conservative estimate of 3262 unique genes. Interspecific comparisons of the predicted proteins support an ancient divergence of clade I nematodes from other nematodes in the phylum Nematoda. Furthermore, apparent clade I or Trichocephalida-specific proteins were identified, which may include molecular determinants important in the evolution of these species. Similarity matches identified 463 C. elegans genes homologs that confer phenotypes by RNA interference. Classification of predicted proteins suggested diverse cellular, metabolic and extracellular functions, significantly expanding the dataset of T. spiralis proteins with prospective, and potentially critical, functions. Several lines of evidence suggested stage-specific expression of certain genes beyond those previously identified. Evidence was obtained for the existence of large gene families encoding isoforms of known secreted proteins, such as p43 and TspE1. Unexpectedly, diverse isoforms of the muscle larva p43 gene appear to be expressed by immature L1. Proteinases, kinases, antioxidant proteins and enzymes involved in glycan synthesis are implicated in T. spiralis interactions with its hosts. Numerous genes were identified that encode predicted proteins in these categories. The genes discovered, when put into context of functional classification, stage of expression, and biology of the parasite, should substantially enhance experimental potential for research on this parasite.

Identification of an astacin-like metallo-proteinase transcript from the infective larvae of Strongyloides stercoralis

Strongyloides stercoralis, an important nematode pathogen of humans, is transmitted by contact with soil contaminated with the microscopic larvae of the parasite. We determined the cDNA sequence and deduced amino acid structure of a metallo-proteinase that is abundantly transcribed expressed by infective stage larvae of S. stercoralis. This deduced structure of the enzyme revealed a multi-domain protein that included an NH2-terminal peptidase. This peptidase consisted of a signal peptide, a pro-enzyme region, and a mature peptidase domain that included the metal ion co-ordinating motifs, HETSHALGVIH and SIMHY ("Met-turn"), characteristic of the catalytic active site of members of the metzincin superfamily of zinc metallo-endopeptidases. It was phylogenetically and structurally similar to astacin from the digestive gland of the crayfish Astacus astacus, to the HCH-1 peptidase of Caenorhabditis elegans required for hatching and migration of a post-embryonic neuroblast, and to the morphogenetically important peptidases, bone morphogenetic protein-1 (BMP-1) and Drosophila tolloid. In addition, the Strongyloides enzyme, designated strongylastacin, includes a central epidermal growth factor (EGF) domain followed by a carboxyl CUB (complement sub component C1r/C1s/embryonic sea urchin protein Uegf/bone morphogenetic protein) domain. Inspection of the dbEST database revealed the presence of at least 9 transcript clusters that are related to greater or lesser extent to strongylastacin; based on these expressed sequence tags, strongylastacin was expressed only in the infective third stage larvae, whereas other transcript clusters were expressed both in filariform and rhabditiform stages or only in the rhabditiform stage. Based on the deduced sequence, structure, and expression profile, strongylastacin is the probable candidate for the zinc-dependent metalloprotease, Ss40, known to be deployed by larvae of S. stercoralis to penetrate human skin to initiate infection.

Developmental regulation and secretion of nematode-specific cysteine-glycine domain proteins in Trichinella spiralis

The muscle larva of Trichinella spiralis is an intracellular parasite of mammalian skeletal muscle, encapsulating within a portion of the myofiber and resulting in muscle de-differentiation. Parasite-derived factors secreted or excreted by the muscle larva are thought to play a role in the formation of the host-parasite complex and in the induction of changes in the host cell. We screened a library enriched for T. spiralis-specific cDNAs and identified a clone encoding a protein with similarity to a predicted secreted or extracellular Caenorhabditis elegans protein. The region of similarity included a conserved cysteine-glycine (CCG) domain, which we have identified as being nematode-specific. This domain is present in the predicted T. spiralis protein, Ts-CCG-1, and in a second protein, Ts-CCG-2, which we identified from subsequent analysis. We showed that while the Ts-ccg-1 gene is constitutively expressed, Ts-ccg-2 gene expression is restricted to the muscle L1 larva. Both predicted proteins contain an N-terminal signal peptide and we subsequently confirmed by MALDI-TOF mass spectrometric analyses of excretory/secretory peptide spots excised from two-dimensional gels that Ts-CCG-2 is secreted.