A nucleotidase with unique catalytic properties is secreted by Trichinella spiralis

Modulation of Host Immunity by Helminths: The Expanding Repertoire of Parasite Effector Molecules

Helminths are extraordinarily successful parasites due to their ability to modulate the host immune response. They have evolved a spectrum of immunomodulatory molecules that are now beginning to be defined, heralding a molecular revolution in parasite immunology. These discoveries have the potential both to transform our understanding of parasite adaptation to the host and to develop possible therapies for immune-mediated disease. In this review we will summarize the current state of the art in parasite immunomodulation and discuss perspectives on future areas for research and discovery.

Ubiquitin-Dependent Modification of Skeletal Muscle by the Parasitic Nematode, Trichinella spiralis

Trichinella spiralis is a muscle-specific parasitic worm that is uniquely intracellular. T. spiralis reprograms terminally differentiated skeletal muscle cells causing them to de-differentiate and re-enter the cell cycle, a process that cannot occur naturally in mammalian skeletal muscle cells, but one that holds great therapeutic potential. Although the host ubiquitin pathway is a common target for viruses and bacteria during infection, its role in parasite pathogenesis has been largely overlooked. Here we demonstrate that the secreted proteins of T. spiralis contain E2 Ub-conjugating and E3 Ub-ligase activity. The E2 activity is attributed to TsUBE2L3, a novel and conserved T. spiralis enzyme located in the secretory organ of the parasite during the muscle stages of infection. TsUBE2L3 cannot function with any T.spiralis secreted E3, but specifically binds to a panel of human RING E3 ligases, including the RBR E3 ARIH2 with which it interacts with a higher affinity than the mammalian ortholog UbcH7/UBE2L3. Expression of TsUBE2L3 in skeletal muscle cells causes a global downregulation in protein ubiquitination, most predominantly affecting motor, sarcomeric and extracellular matrix proteins, thus mediating their stabilization with regards to proteasomal degradation. This effect is not observed in the presence of the mammalian ortholog, suggesting functional divergence in the evolution of the parasite protein. These findings demonstrate the first example of host-parasite interactions via a parasite-derived Ub conjugating enzyme; an E2 that demonstrates a novel muscle protein stabilization function.

Parasitic worms often establish long-lasting infections in their hosts; tightly regulating their surroundings to strike a delicate balance between host cell modulation and protection that will ensure their replication. This is accomplished via the active secretion of parasite glycolipids and glycoproteins into the host. Trichinella spiralis, a parasitic nematode that infects skeletal muscle of mammals, birds and reptiles, is the only parasitic worm with a true intracellular stage. T. spiralis invade terminally differentiated myotubes, reprogramming them to de-differentiate and re-enter the cell cycle, a process that cannot occur naturally in mammalian skeletal muscle cells, but one that holds great therapeutic potential. We have identified and characterized a novel T. spiralis secreted protein that, despite a high level of sequence identity, appears to have evolved a different function to its host ortholog. This protein is an active Ub conjugating enzyme that binds to a panel of human E3 Ub ligases with higher affinity than the host ortholog. Furthermore, when expressed in skeletal muscle cells in culture, its presence uniquely leads to the stabilization of muscle-specific proteins via the downregulation of their ubiquitination.

Host parasite communications-Messages from helminths for the immune system: Parasite communication and cell-cell interactions

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Helminth parasites release a spectrum of mediators to dampen host immunity.

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Secreted proteins can act on host receptors and intracellular signalling.

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Parasites also produce exosome-like extracellular vesicles containing microRNAs.

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Exosomes can enter host cells and modulate host gene expression.

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Extracellular vesicles may be a more general mode of host-parasite interaction.

Helminths are metazoan organisms many of which have evolved parasitic life styles dependent on sophisticated manipulation of the host environment. Most notably, they down-regulate host immune responses to ensure their own survival, by exporting a range of immuno-modulatory mediators that interact with host cells and tissues. While a number of secreted immunoregulatory parasite proteins have been defined, new work also points to the release of extracellular vesicles, or exosomes, that interact with and manipulate host gene expression. These recent results are discussed in the overall context of how helminths communicate effectively with the host organism.

Shared weapons of blood- and plant-feeding insects: Surprising commonalities for manipulating hosts

Insects that reprogram host plants during colonization remind us that the insect side of plant-insect story is just as interesting as the plant side. Insect effectors secreted by the salivary glands play an important role in plant reprogramming. Recent discoveries point to large numbers of salivary effectors being produced by a single herbivore species. Since genetic and functional characterization of effectors is an arduous task, narrowing the field of candidates is useful. We present ideas about types and functions of effectors from research on blood-feeding parasites and their mammalian hosts. Because of their importance for human health, blood-feeding parasites have more tools from genomics and other - omics than plant-feeding parasites. Four themes have emerged: (1) mechanical damage resulting from attack by blood-feeding parasites triggers "early danger signals" in mammalian hosts, which are mediated by eATP, calcium, and hydrogen peroxide, (2) mammalian hosts need to modulate their immune responses to the three "early danger signals" and use apyrases, calreticulins, and peroxiredoxins, respectively, to achieve this, (3) blood-feeding parasites, like their mammalian hosts, rely on some of the same "early danger signals" and modulate their immune responses using the same proteins, and (4) blood-feeding parasites deploy apyrases, calreticulins, and peroxiredoxins in their saliva to manipulate the "danger signals" of their mammalian hosts. We review emerging evidence that plant-feeding insects also interfere with "early danger signals" of their hosts by deploying apyrases, calreticulins and peroxiredoxins in saliva. Given emerging links between these molecules, and plant growth and defense, we propose that these effectors interfere with phytohormone signaling, and therefore have a special importance for gall-inducing and leaf-mining insects, which manipulate host-plants to create better food and shelter.

Characterization and functional analysis of Trichinella spiralis Nudix hydrolase

Trichinella spiralis Nudix hydrolase (TsNd) was identified by screening a T7 phage display cDNA library from T. spiralis intestinal infective larvae (IIL), and vaccination of mice with recombinant TsNd protein (rTsNd) or TsNd DNA vaccine produced a partial protective immunity. The aim of this study was to identify the characteristics and biological functions of TsNd in the process of invasion and development of T. spiralis larvae. Transcription and expression of TsNd gene at all developmental stages of T. spiralis were observed by qPCR and immunofluorescent test (IFT). The rTsNd had the Nd enzymatic activity to dGTP, NAD, NADP and CoA. Its kinetic properties on the preferred substrate dGTP were calculated, and the Vmax, Km, and kcat/Km values at pH 8.0 were 3.19 μM min(-1) μg(-1), 370 μM, and 144 s(-1) M(-1), respectively, in reaction matrix containing 5 mM Zn(2+) and 2 mM DTT. The rTsNd was active from 25 °C to 50 °C, with optimal activity at 37 °C. rTsNd was able to bind specifically to mouse intestinal epithelial cells (IECs) and promoted the larval invasion of IECs, whereas anti-rTsNd antibodies inhibited the larval invasion of IECs in a dose-dependent manner. Anti-rTsNd antibodies could kill T. spiralis infective larvae by an ADCC-mediated mechanism. Our results showed that the rTsNd protein was able to interact with host IECs, had the Nudix hydrolasing activity and the enzymatic activity appeared to be essential indispensable for the T. spiralis larval invasion, development and survival in host.

Immune modulation by helminth parasites of ruminants: implications for vaccine development and host immune competence

Parasitic helminths reside in immunologically-exposed extracellular locations within their hosts, yet they are capable of surviving for extended periods. To enable this survival, these parasites have developed complex and multifaceted mechanisms to subvert or suppress host immunity. This review summarises current knowledge of immune modulation by helminth parasites of ruminants and the parasite-derived molecules involved in driving this modulation. Such immunomodulatory molecules have considerable promise as vaccine targets, as neutralisation of their function is predicted to enhance anti-parasite immunity and, as such, current knowledge in this area is presented herein. Furthermore, we summarise current evidence that, as well as affecting parasite-specific immunity, immune modulation by these parasites may also affect the ability of ruminant hosts to control concurrent diseases or mount effective responses to vaccination.

Characterisation of a plancitoxin-1-like DNase II gene in Trichinella spiralis

Background

Deoxyribonuclease II (DNase II) is a well-known acidic endonuclease that catalyses the degradation of DNA into oligonucleotides. Only one or a few genes encoding DNase II have been observed in the genomes of many species. 125 DNase II-like protein family genes were predicted in the Trichinella spiralis (T. spiralis) genome; however, none have been confirmed. DNase II is a monomeric nuclease that contains two copies of a variant HKD motif in the N- and C-termini. Of these 125 genes, only plancitoxin-1 (1095 bp, GenBank accession no. XM_003370715.1) contains the HKD motif in its C-terminus domain.

Methodology/Principal Findings

In this study, we cloned and characterised the plancitoxin-1 gene. However, the sequences of plancitoxin-1 cloned from T. spiralis were shorter than the predicted sequences in GenBank. Intriguingly, there were two HKD motifs in the N- and C-termini in the cloned sequences. Therefore, the gene with shorter sequences was named after plancitoxin-1-like (Ts-Pt, 885 bp) and has been deposited in GenBank under accession number KF984291. The recombinant protein (rTs-Pt) was expressed in a prokaryotic expression system and purified by nickel affinity chromatography. Western blot analysis showed that rTs-Pt was recognised by serum from T. spiralis-infected mice; the anti-rTs-Pt serum recognised crude antigens but not ES antigens. The Ts-Pt gene was examined at all T. spiralis developmental stages by real-time quantitative PCR. Immunolocalisation analysis showed that Ts-Pt was distributed throughout newborn larvae (NBL), the tegument of adults (Ad) and muscle larvae (ML). As demonstrated by DNase zymography, the expressed proteins displayed cation-independent DNase activity. rTs-Pt had a narrow optimum pH range in slightly acidic conditions (pH 4 and pH 5), and its optimum temperature was 25°C, 30°C, and 37°C.

Conclusions

This study indicated that Ts-Pt was classified as a somatic protein in different T. spiralis developmental stages, and demonstrated for the first time that an expressed DNase II protein from T. spiralis had nuclease activity.

Deoxyribonuclease II (DNase II) is classified into a unique family of nucleases and mediates the degradation of DNA associated with apoptosis. Although DNase II activity was first observed in 1947, and has been studied biochemically and enzymatically since the 1960s, only recently has genetic information on the enzyme been reported. Compared with enzymes from other species, including C. elegans, the DNase II-like protein family of the parasitic nematode T. spiralis has expanded remarkably, with an estimated 125 genes found in the draft genome of T. spiralis. However, none of these proteins have been confirmed by biochemical studies. This study describes Ts-Pt, a DNase II protein that is expressed in different T. spiralis developmental stages. The recombinant protein purified via a prokaryotic expression system displayed in vitro nuclease activity, as determined by DNase zymography. The exact function and mechanisms of Ts-Pt should be further explored in vivo.

Cloning and expression of apyrase gene from Ancylostoma caninum in Escherechia coli

Apyrase encoding metal-ions activated plasma membrane protease is present in animal and plant tissues. This enzyme can hydrolyze ADP and ATP pyrophosphate bond, resulting in AMP and free phosphate groups, and plays an important role for insects and parasites to evade host immune system. However localization and function of apyrase in the canine hookworm, Ancylostoma caninum, remains unknown. To analyze apyrase gene in A. caninum (a eukaryotic parasitic hookworm), a pair of primers was designed according to the previous EST data. The full-length cDNA of apyrase gene was amplified from A. caninum by RT-PCR. The partial cDNA of apyrase encodes 249 amino acid protein was expressed in Escherechia coli. The recombinant protein was induced to express under proper conditions and the molecular size was as expected. The recombinant protein was purified. The transcripts of apyrase in different stages of A. caninum were analyzed by the Real-time PCR assay, and Immuno-localization assays were used to research the protein expression in different stages of A. caninum.

Cellular function and molecular structure of ecto-nucleotidases

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

Trichinella spiralis secreted enzymes regulate nucleotide-induced mast cell activation and release of mouse mast cell protease 1

Extracellular nucleotides are important triggers of innate immunity, acting on a wide variety of cells via signaling through purinergic receptors. Mucosal mast cells contribute to expulsion of a number of gastrointestinal nematode parasites, and mouse mast cell protease 1 has been shown to have a critical role in clearance of Trichinella spiralis from the intestinal tract. We show here that adenosine, ADP, ATP, UDP, and UTP all stimulate calcium mobilization in bone marrow-derived mast cells with a mucosal phenotype. Secreted proteins from T. spiralis infective larvae inhibit nucleotide-induced mast cell activation, and that induced by ADP and UDP is specifically blocked by parasite secretory 5'-nucleotidase. Release of mouse mast cell protease 1 is stimulated by ADP and ATP. Both parasite secreted products and the 5'-nucleotidase inhibit ADP-induced release of mast cell protease, whereas that stimulated by ATP is partially inhibited by secreted products alone. This indicates that the 5'-nucleotidase contributes to but is not solely responsible for inhibition of nucleotide-mediated effects on mast cell function. Secretion of nucleotide-metabolizing enzymes by parasitic nematodes most likely evolved as a strategy for suppression of innate immune responses and is discussed in this context.

Comparative analysis of excretory-secretory antigens of Trichinella spiralis and Trichinella britovi muscle larvae by two-dimensional difference gel electrophoresis and immunoblotting

Background

Trichinellosis is a zoonotic disease in humans caused by Trichinella spp. The present study was undertaken to discover excretory-secretory (E-S) proteins from T. spiralis and T. britovi muscle larvae (ML) that hold promise for species-specific diagnostics. To that end, the purified E-S proteins were analyzed by fluorescent two-dimensional difference gel electrophoresis (2-D DIGE) coupled with protein identification by liquid chromatography-tandem mass spectrometry (LC-MS/MS). To search for immunoreactive proteins that are specifically recognized by host antibodies the E-S proteins were subjected to two-dimensional (2-DE) immunoblotting with antisera derived from pigs experimentally infected with T. spiralis or T. britovi.

Results

According to 2-D DIGE analysis, a total of twenty-two proteins including potentially immunogenic proteins and proteins produced only by one of the two Trichinella species were subjected to LC-MS/MS for protein identification. From these proteins seventeen could be identified, of which many were identified in multiple spots, suggesting that they have undergone post-translational modification, possibly involving glycosylation and/or proteolysis. These proteins included 5'-nucleotidase, serine-type protease/proteinase, and p43 glycoprotein (gp43) as well as 49 kDa E-S protein (p49). Our findings also suggest that some of the commonly identified proteins were post-translationally modified to different extents, which in certain cases seemed to result in species-specific modification. Both commonly and specifically recognized immunoreactive proteins were identified by 2-DE immunoblotting; shared antigens were identified as gp43 and different protease variants, whereas those specific to T. britovi included multiple isoforms of the 5'-nucleotidase.

Conclusions

Both 2-D DIGE and 2-DE immunoblotting approaches indicate that T. spiralis and T. britovi produce somewhat distinctive antigen profiles, which contain E-S antigens with potential as species-specific diagnostic markers for Trichinella. Our results also demonstrate the value of 2-D DIGE as a versatile tool to compare secretomes of different Trichinella species for pinpointing factors contributing to the interaction with the host.

A calcium-activated nucleotidase secreted from Ostertagia ostertagi 4th-stage larvae is a member of the novel salivary apyrases present in blood-feeding arthropods

Apyrases (ATP-diphosphohydrolase) comprise a ubiquitous class of glycosylated nucleotidases that hydrolyse extracellular ATP and ADP to orthophosphate and AMP. One class of newly-described, Ca2+-dependent, salivary apyrases known to counteract blood-clotting, has been identified in haematophagous arthropods. Herein, we have identified a gene (Oos-apy-1) encoding a protein that structurally conforms to the Ca2+-activated apyrase from the bed bug, Cimex lectularius, by immunologically screening an Ostertagia L4 cDNA expression library. The expressed protein (rOos-APY-1) was biochemically functional in the presence of Ca2+ only, with greatest activity on ATP, ADP, UTP and UDP. Host antibodies to the fusion protein appeared as early as 14 days post-infection (p.i.) and increased through 30 days p.i. Immunohistochemical and Western blot analyses demonstrated that the native Oos-APY-1 protein is present in the glandular bulb of the oesophagus and is confined to the L4. A putative signal sequence at the N-terminus and near 100% identity with a Teladorsagia circumcincta L4 secreted protein is consistent with the native protein being secreted at the cellular level. Predicated upon substrate specificity, the native protein may be used by the parasite to control the levels of host extracellular nucleotides released by locally-damaged tissues in an effort to modulate immune intervention and inflammation.

A calcium-activated apyrase from Teladorsagia circumcincta: an excretory/secretory antigen capable of modulating host immune responses?

A cDNA representing the gene Teladorsagia circumcincta apyrase-1 (Tci-apy-1) was isolated, by PCR, from a T. circumcincta fourth-stage larval (L4) cDNA library. The closest orthologue of this gene is a Ca(2+)-dependent apyrase from Ostertagia ostertagi, with 92% amino acid identity across all 339 residues. Tci-apy-1 is transcribed in a stage-specific manner, the transcript being predominant in L4, detectable in the adult cDNA, but absent from eggs and infective third-stage larvae (L3). The protein, Tci-APY-1, was detected by immunoblotting in extracts of L4 nematodes and was present in excretory/secretory products from the same developmental stage. A recombinant version of Tci-APY-1 was expressed in bacteria as an active enzyme that hydrolysed nucleoside triphosphate substrates with a preference of ATP over other nucleoside triphosphates. Recombinant Tci-APY-1 hydrolysed ATP and ADP but not AMP. Apyrase activity was divalent cation-dependent, with no hydrolysis in the presence of Mg(2+), but activation in the presence of Ca(2+). Recombinant Tci-APY-1 was bound by IgG present in serum and both IgG and IgA present in abomasal mucus from trickle-infected, immune sheep but not in material derived from lambs exposed to a single infection. The potential immunomodulatory roles of this Tci-APY-1 are discussed in relation to purinergic signalling.

Functional and small-angle X-ray scattering studies of a new stationary phase survival protein E (SurE) from Xylella fastidiosa--evidence of allosteric behaviour

The genome data of bacterium Xylella fastidiosa strain 9a5c has identified several orfs related to its phytopathogenic adaptation and survival. Among these genes, the surE codifies a survival protein E (XfSurE) whose function is not so well understood, but functional assays in Escherichia coli revealed nucleotidase and exopolyphosphate activity. In the present study, we report the XfSurE protein overexpression in E. coli and its purification. The overall secondary structure was analyzed by CD. Small-angle X-ray scattering and gel filtration techniques demonstrated that the oligomeric state of the protein in solution is a tetramer. In addition, functional kinetics experiments were carried out with several monophosphate nucleoside substrates and revealed a highly positive cooperativity. An allosteric mechanism involving torsion movements in solution is proposed to explain the cooperative behaviour of XfSurE. This is the first characterization of a SurE enzyme from a phytopathogen organism and, to our knowledge, the first solution structure of a SurE protein to be described.

Helminth immunoregulation: the role of parasite secreted proteins in modulating host immunity

Helminths are masterful immunoregulators. A characteristic feature of helminth infection is a Th2-dominated immune response, but stimulation of immunoregulatory cell populations, such as regulatory T cells and alternatively activated macrophages, is equally common. Typically, Th1/17 immunity is blocked and productive effector responses are muted, allowing survival of the parasite in a "modified Th2" environment. Drug treatment to clear the worms reverses the immunoregulatory effects, indicating that a state of active suppression is maintained by the parasite. Hence, research has focussed on "excretory-secretory" products released by live parasites, which can interfere with every aspect of host immunity from initial recognition to end-stage effector mechanisms. In this review, we survey our knowledge of helminth secreted molecules, and summarise current understanding of the growing number of individual helminth mediators that have been shown to target key receptors or pathways in the mammalian immune system.

Parasitic helminths: a pharmacopeia of anti-inflammatory molecules

Infection with parasitic helminths takes a heavy toll on the health and well-being of humans and their domestic livestock, concomitantly resulting in major economic losses. Analyses have consistently revealed bioactive molecules in extracts of helminths or in their excretory/secretory products that modulate the immune response of the host. It is our view that parasitic helminths are an untapped source of immunomodulatory substances that, in pure form, could become new drugs (or models for drug design) to treat disease. Here, we illustrate the range of immunomodulatory molecules in selected parasitic trematodes, cestodes and nematodes, their impact on the immune cells in the host and how the host may recognize these molecules. There are many examples of the partial characterization of helminth-derived immunomodulatory molecules, but these have not yet translated into new drugs, reflecting the difficulty of isolating and fully characterizing proteins, glycoproteins and lipid-based molecules from small amounts of parasite material. However, this should not deter the investigator, since analytical techniques are now being used to accrue considerable structural information on parasite-derived molecules, even when only minute quantities of tissue are available. With the introduction of methodologies to purify and structurally-characterize molecules from small amounts of tissue and the application of high throughput immunological assays, one would predict that an assessment of parasitic helminths will yield a variety of novel drug candidates in the coming years.

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.

Comparative analysis of the excretory-secretory proteome of the muscle larva of Trichinella pseudospiralis and Trichinella spiralis

The nematodes Trichinella spiralis and Trichinella pseudospiralis are both intracellular parasites of skeletal muscle cells and induce profound alterations in the host cell resulting in a re-alignment of muscle-specific gene expression. While T. spiralis induces the production of a collagen capsule surrounding the host-parasite complex, T. pseudospiralis exists in a non-encapsulated form and is also characterised by suppression of the host inflammatory response in the muscle. These observed differences between the two species are thought to be due to variation in the proteins excreted or secreted (ES proteins) by the muscle larva. In this study, we use a global proteomics approach to compare the ES protein profiles from both species and to identify individual T. pseudospiralis proteins that complement earlier studies with T. spiralis. Following two-dimensional gel electrophoresis, tandem mass spectrometry was used to identify the peptide spots. In many cases identification was aided by the determination of partial peptide sequence from selected mass ions. The T. pseudospiralis spots identified included the major secreted glycoproteins and the secreted 5'-nucleotidase. Furthermore, two major groups of T. spiralis-specific proteins and several T. pseudospiralis-specific proteins were identified. Our results demonstrate the value of proteomics as a tool for the identification of ES proteins that are differentially expressed between Trichinella species and as an aid to identifying key parasite proteins that are involved in the host-parasite interaction. The value of this approach will be further enhanced by data arising out the current T. spiralis genome sequencing project.

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.

Characterisation of a secreted N-acetyl-β-hexosaminidase from Trichinella spiralis

A thorough investigation was conducted for glycoside hydrolase activities in the secreted proteins of Trichinella spiralis. The data demonstrated that the only secreted glycosidase with significant activity was an exo-beta-hexosaminidase with catalysis of the substrates N-acetyl-beta-D-glucosamine, N-acetyl-beta-D-galactosamine and N-acetyl-beta-D-glucosamine-6-sulphate proceeding with an efficiency similar to the human isozyme beta-hexosaminidase A (Hex A). The hydrolysis of N-acetyl-beta-D-glucosamine followed Michaelis-Menten kinetics with a K(m) of 0.187+/-0.025 mM, and catalysis was inhibited competitively by both N-acetyl-beta-d-glucosamine and N-acetyl-beta-D-galactosamine, with K(i) values of 15.75+/-0.99 and 1.17+/-0.24 mM, respectively. The enzyme was maximally active at pH 4.4, had a temperature optimum at 54 degrees C and was thermolabile. We observed no cleavage of N-acetylglucosamine beta1-4 linkages in N-acetylchitooligosaccharides, but significant hydrolysis of N-acetylglucosamine beta1-2 linked to mannose in glycans was detected indicating that the secreted enzyme is linkage specific. The enzyme was partially purified and identified by SDS-PAGE and Western blotting as a protein with an apparent molecular mass of 50 kDa. We established that the protein was glycosylated and showed that the glycan was decorated with tyvelose (3,6-dideoxy-D-arabino-hexose). Matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) analysis demonstrated that the carbohydrate moeity was a tyvelose capped tetra-antennary N-glycan corresponding to the structure Tyv(4)Fuc(5)HexNAc(10)Hex(3). All our studies suggest that this is a novel variant of a secreted N-acetyl-beta-hexosaminidase.