Purification and characterisation of a secreted aminopeptidase from adult Ascaris suum

Ascaris suum Informs Extrasynaptic Volume Transmission in Nematodes

Neural circuit synaptic connectivities (the connectome) provide the anatomical foundation for our understanding of nematode nervous system function. However, other nonsynaptic routes of communication are known in invertebrates including extrasynaptic volume transmission (EVT), which enables short- and/or long-range communication in the absence of synaptic connections. Although EVT has been highlighted as a facet of Caenorhabditis elegans neurosignaling, no experimental evidence identifies body cavity fluid (pseudocoelomic fluid; PCF) as a vehicle for either neuropeptide or biogenic amine transmission. In the parasitic nematode Ascaris suum, FMRFamide-like peptides encoded on flp-18 potently stimulate female reproductive organs but are expressed in cells that are anatomically distant from the reproductive organ, with no known synaptic connections to this tissue. Here we investigate nonsynaptic neuropeptide signaling in nematodes mediated by the body cavity fluid. Our data show that (i) A. suum PCF (As-PCF) contains a catalog of neuropeptides including FMRFamide-like peptides and neuropeptide-like proteins, (ii) the A. suum FMRFamide-like peptide As-FLP-18A dominates the As-PCF peptidome, (iii) As-PCF potently modulates nematode reproductive muscle function ex vivo, mirroring the effects of synthetic FLP-18 peptides, (iv) As-PCF activates the C. elegans FLP-18 receptors NPR-4 and -5, (v) As-PCF alters C. elegans behavior, and (vi) FLP-18 and FLP-18 receptors display pan-phylum distribution in nematodes. This study provides the first direct experimental evidence to support an extrasynaptic volume route for neuropeptide transmission in nematodes. These data indicate nonsynaptic signaling within the nematode functional connectome and are particularly pertinent to receptor deorphanization approaches underpinning drug discovery programs for nematode pathogens.

Genomic Signatures of Coevolution between Nonmodel Mammals and Parasitic Roundworms

Antagonistic coevolution between host and parasite drives species evolution. However, most of the studies only focus on parasitism adaptation and do not explore the coevolution mechanisms from the perspective of both host and parasite. Here, through the de novo sequencing and assembly of the genomes of giant panda roundworm, red panda roundworm, and lion roundworm parasitic on tiger, we investigated the genomic mechanisms of coevolution between nonmodel mammals and their parasitic roundworms and those of roundworm parasitism in general. The genome-wide phylogeny revealed that these parasitic roundworms have not phylogenetically coevolved with their hosts. The CTSZ and prolyl 4-hydroxylase subunit beta (P4HB) immunoregulatory proteins played a central role in protein interaction between mammals and parasitic roundworms. The gene tree comparison identified that seven pairs of interactive proteins had consistent phylogenetic topology, suggesting their coevolution during host–parasite interaction. These coevolutionary proteins were particularly relevant to immune response. In addition, we found that the roundworms of both pandas exhibited higher proportions of metallopeptidase genes, and some positively selected genes were highly related to their larvae’s fast development. Our findings provide novel insights into the genetic mechanisms of coevolution between nonmodel mammals and parasites and offer the valuable genomic resources for scientific ascariasis prevention in both pandas.

Differential proteolytic activity in Anisakis simplex s.s. and Anisakis pegreffii, two sibling species from the complex Anisakis simplex s.l., major etiological agents of anisakiasis

Proteolytic activity was studied in two sibling species of Anisakis (Nematoda: Anisakidae), A. simplex s.s. and A. pegreffii, throughout their in vitro development from third larval stage (L3) from the host fish (L3-0h) to fourth larval stage (L4) obtained in culture. Proteases have a significant role in the lifecycle of the parasite and in the pathogen-host relationship. Proteolytic activity peaks were detected at pH 6.0 and 8.5. Protease activity was detected in all the developmental stages of the two species studied at both pH values. These pH values were used for assaying with specific inhibitors which permitted the determination of metalloprotease activity, and, to a lesser extent, that of serine and cysteine protease. Aspartic protease activity was only detected at pH 6.0. At this pH, L4 larvae showed higher proteolytic activity than L3 larvae in both species (p < 0.001), the majority of activity being due to metalloproteases and aspartic proteases, which could be related to nutrition, especially the latter, as occurs in invertebrates. At pH 8.5, proteolytic activity was higher in A. simplex s.s. than in A. pegreffii (p < 0.01). At this pH, the majority of activity was due to metalloproteases in all developmental phases of both species, although, in L3-0h, the activity of these proteases was significantly higher (p < 0.03) in A. simplex s.s. than in A. pegreffii. This could be related to the greater invasive capacity of the former. Serine proteases have frequently been implicated in the invasive capacity and pathogenicity of some parasites. This may be related to the significantly higher activity (p ≤ 0.05) of serine protease in all the larval stages of A. simplex studied at pH 6.0. Thus, there are interspecific differences in proteases that have been related to pathogenesis in nematodes. These differences could thus be contributing to the previously reported differences in pathogenicity between these two Anisakis species.

Biological role of excretory-secretory proteins in endemic parasites of Latin America and the Caribbean

Neglected tropical diseases (NTDs) share certain traits: they are parasitic infections, prevailing in tropical environments and affecting marginalized sectors of the population. Six NTDs - ascariasis, cysticercosis, echinococcosis, hookworm infection, onchocerciasis and trichuriasis - all of them endemic in Latin America and the Caribbean (LAC), are analysed in this work. This review aims to discuss key information on the function of excretory/secretory (E/S) proteins from these parasites in their infectivity, pathogeny and diagnosis. The modulation of the host immune system to favour the permanence and survival of the parasite is also discussed. An updated knowledge on the function of E/S molecules in endemic parasitoses in LAC may lead to new approaches for the clinical management and diagnosis of these diseases. In turn, this could allow us to optimize their treatment and make it more affordable - a relevant goal given the economic constraints that the region is facing.

Molecular cloning and characterization of leucine aminopeptidase gene from Taenia pisiformis

Leucine aminopeptidase (LAP, EC: 3.4.11.1) is an important metalloexopeptidase that catalyze the hydrolysis of amino-terminal leucine residues from polypeptides and proteins. In this study, a full length of cDNA encoding leucine aminopeptidase of Taenia pisiformis (TpLAP) was cloned by rapid amplification of cDNA-ends using the polymerase chain reaction (RACE-PCR) method. The full-length cDNA of the TpLAP gene is 1823 bp and contains a 1569 bp ORF encoding 533 amino acids with a putative mass of 56.4 kDa. TpLAP contains two characteristic motifs of the M17LAP family in the C-terminal sequence: the metal binding site 265-[VGKG]-271 and the catalytic domain motif 351-[NTDAEGRL]-357. The soluble GST-TpLAP protein was expressed in Escherichia coli Transetta (DE3) and four specific anti-TpLAP monoclonal antibodies (mAbs) were prepared. In enzymatic assays, the optimal activity was observed at pH 9.5 at 45 °C. GST-TpLAP displayed a hydrolyzing activity for the Leu-pNA substrate with a maximum activity of 46 U/ml. The enzymatic activity was significantly enhanced by Mn²⁺ and completely inhibited by 20 nM bestatin and 0.15 mM EDTA. The native TpLAP was detected specifically in ES components of adult T. pisiformis by western blotting using anti-TpLAP mAb as a probe. Quantitative real-time PCR revealed that the TpLAP gene was expressed at a high level in adult worm tissues, especially in the gravid proglottids (50.71-fold). Immunolocalization analysis showed that TpLAP was located primarily in the subtegumental parenchyma zone and the uterine wall of adult worms. Our results indicate that TpLAP is a new member of the M17LAP family and can be considered as a stage-differentially expressed protein. These findings might provide new insights into the study of the mechanisms of growth, development and survival of T. pisiformis in the final host and have potential value as an attractive target for drug therapy or vaccine intervention.

Proteomic analysis of adult Ascaris suum fluid compartments and secretory products

Background

Strategies employed by parasites to establish infections are poorly understood. The host-parasite interface is maintained through a molecular dialog that, among other roles, protects parasites from host immune responses. Parasite excretory/secretory products (ESP) play major roles in this process. Understanding the biology of protein secretion by parasites and their associated functional processes will enhance our understanding of the roles of ESP in host-parasite interactions.

Methodology/Principal Findings

ESP was collected after culturing 10 adult female Ascaris suum. Perienteric fluid (PE) and uterine fluid (UF) were collected directly from adult females by dissection. Using SDS-PAGE coupled with LC-MS/MS, we identified 175, 308 and 274 proteins in ESP, PE and UF, respectively. Although many proteins were shared among the samples, the protein composition of ESP was distinct from PE and UF, whereas PE and UF were highly similar. The distribution of gene ontology (GO) terms for proteins in ESP, PE and UF supports this claim. Comparison of ESP composition in A. suum, Brugia malayi and Heligmosoides polygyrus showed that proteins found in UF were also secreted by males and by larval stages of other species, suggesting that multiple routes of secretion may be used for homologous proteins. ESP composition of nematodes is both phylogeny- and niche-dependent.

Conclusions/Significance

Analysis of the protein composition of A. suum ESP and UF leads to the conclusion that the excretory-secretory apparatus and uterus are separate routes for protein release. Proteins detected in ESP have distinct patterns of biological functions compared to those in UF. PE is likely to serve as the source of the majority of proteins in UF. This analysis expands our knowledge of the biology of protein secretion from nematodes and will inform new studies on the function of secreted proteins in the orchestration of host-parasite interactions.

Ascaris lumbricoides, the most prevalent metazoan parasite of humans, is a public health concern in resource-limited countries. Survival of this parasite in its host is mediated at least in part by parasite materials secreted into the host. Little is known about the composition of these secretions; defining their contents and functions will illuminate host-parasite interactions that lead to parasite establishment. Ascaris suum, a parasite of pigs, was used as a model organism because its genome has been sequenced and it is very closely related to A. lumbricoides. Excretory/secretory products (ESP), uterine fluid (UF) and perienteric fluid (PE) were collected from adult A. suum. Proteins were subjected to LC-MS/MS. ESP proteins (the ‘secretome’) included many also present in UF. Proteins in ESP but not in UF had considerably different characteristics than those in PE or UF, which were similar to each other. We conclude that proteins released from the secretory apparatus have distinct patterns of biological function and that UF proteins are likely derived from PE. Comparing the protein composition of A. suum ESP to ESP from B. malayi and H. polygyrus suggests that the secretome is conserved at the level of both phylogeny and host predilection site.

Molecular characterization of Trichinella spiralis aminopeptidase and its potential as a novel vaccine candidate antigen against trichinellosis in BALB/c mice

Background

Trichinella spiralis is an intracellular parasite that can cause a serious threat to human health by causing trichinellosis. The aminopeptidase (AP) was found in the proteins produced by T. spiralis infective larvae after in vitro co-culture with intestinal epithelial cells, but its characteristics and function are unknown. The purpose of this study was to identify the T. spiralis aminopeptidase (TsAP) and to investigate its potential as a vaccine candidate antigen against T. spiralis infection.

Methods

T. spiralis aminopeptidase (TsAP) gene encoding a 54.7 kDa protein was cloned and expressed in Escherichia coli, and purified recombinant TsAP protein was used to immunize BALB/c mice. The antibodies obtained were used to determine where TsAP was localized in the parasite. Transcription and expression of TsAP in different developmental stages of T. spiralis were observed by RT-PCR and Immunofluorescence test (IFT). The immune protection of recombinant TsAP protein against T. spiralis infection in BALB/c mice was evaluated.

Results

Anti-TsAP antibodies recognized the native protein migrating at 54.7 kDa by Western blotting of the crude antigens from muscle larvae. Transcription and expression of TsAP gene was observed in different developmental stages (adult worms, newborn larvae, pre-encapsulated larvae and muscle larvae). TsAP appears to be a cytoplasmic protein located primarily at the cuticle and internal organs of this parasite. After a challenge infection with T. spiralis infective larvae, mice immunized with the recombinant TsAP protein displayed a 38.1% reduction in adult worm burden and 59.1% reduction in muscle larval burden.

Conclusions

In this study, T. spiralis aminopeptidase (TsAP) was first characterized and will help reveal its potential biological functions. TsAP is a novel potential vaccine candidate antigen that merits further investigation.

Proteolytic activity in Hysterothylacium aduncum (Nematoda: Anisakidae), a fish gastrointestinal parasite of worldwide distribution

Proteases have a significant role in the life cycle of parasites and the pathogen-host relationship, being regarded as important virulence factors. In the parasitic nematode Hysterothylacium aduncum proteolytic activity was measured during in vitro development from third larval stage (L3) to mature adult, using DQ red casein as a fluorogenic substrate. Proteolytic activity was detected in all the developmental stages studied and at all pH values within the range employed (2.0-7.5). The assay with specific inhibitors permitted the determination of metalloprotease activity, and, to a lesser extent, that of aspartate- and cysteine-protease. Serine-protease activity was the lowest of those studied. In L3 recently collected from the host fish (L3-0 h), the greatest activity was found at an optimum pH of 4.0 and was mainly inhibited by 1,10-phenathroline (metalloprotease inhibitor). This metalloprotease activity in L3-0 h (infective stage) may be related to the invasion of the host tissues by this larva. In the other developmental stages, the greatest protease activity was found at pH 5.5, although at pH 4.0 a lower activity peak was detected. On the other hand, our data show that the proteolytic activity of the nematode varies according to the presence of pepsin (an aspartic-protease) in the culture medium. Thus, at pH 4.0, activity was greater in the absence of pepsin, with increasing aspartic-protease activity. Together with the detection of aspartic-, cysteine- and metallo-protease (enzymes involved in digestion in invertebrates) in all the developmental stages of the parasite taking place in the digestive tract of the host fish, this allows us to suggest that the pepsin in the culture medium mimics the predigestion conditions in the habitat of the worm within the host and that the activity detected may have, amongst others, a digestive function.

Lack of protective efficacy in buffaloes vaccinated with Fasciola gigantica leucine aminopeptidase and peroxiredoxin recombinant proteins

Gene coding for leucine aminopeptidase (LAP), a metalloprotease, was identified in the tropical liver fluke, Fasciola gigantica; that on sequence analysis showed a close homology (98.6%) with leucine aminopeptidase of the temperate liver fluke, Fasciola hepatica. The recombinant leucine aminopeptidase protein was expressed in Escherichia coli. F. gigantica peroxiredoxin, a hydrogen peroxide scavenger and an immunomodulating protein, was also cloned and expressed in E. coli. A vaccination trial in buffaloes was conducted with these two recombinant proteins, with 150 and 300 μg of leucine aminopeptidase and a cocktail of 150 μg each of recombinant leucine aminopeptidase and peroxiredoxin in three groups, respectively. Both Th1- and Th2-associated humoral immune responses were elicited to immunization with these antigens. A challenge study with 400 metacercariae did not show a significant protection in terms of reduction in the worm burden (8.4%) or anti-fecundity/embryonation effect in the immunized groups, as to the non-immunized control animals. Our observations in this buffalo vaccination trial are contrary to the earlier promise shown by leucine aminopeptidase of F. hepatica as a leading candidate vaccine molecule. Identification of leucine aminopeptidase gene and evaluation of the protein for its protective efficacy in buffaloes is the first scientific report on this protein in F. gigantica.

Biochemical study and in vitro insect immune suppression by a trypsin-like secreted protease from the nematode Steinernema carpocapsae

A trypsin-like serine protease was purified by gel filtration and anion-exchange chromatography from the excretory-secretory products of parasitic phase Steinernema carpocapsae. The purified protease exhibited a molecular mass of about 29 kDa by SDS-PAGE and displayed a pI of 6.3. This protease exhibited high activity with trypsin-specific substrate N-Ben-Phe-Val-Arg-p-nitroanilide and was highly sensitive to aprotinin and benzamidine. The purified trypsin protease digested the chromogenic substrate N-Ben-Phe-Val-Arg-p-nitroanilide with K(m), V(max) and k(cat) values of 594.2 mum, 0.496 mum/min and 22.8/s, respectively. The optimal pH and temperature for protease activity were 9 and 30 degrees C, respectively. Internal amino acid sequencing yielded 150 amino acids and these were homologous to other trypsin sequences. In vitro investigation was carried out to monitor prophenoloxidase suppression in Galleria mellonella by the purified protease; about 38.9-52.6% suppression of prophenoloxidase was observed. The purified protease affected insect haemocyte spreading, causing cells to become spherical or round. Protease-treated actin filaments were highly disorganized in haemocytes. In vitro, G. mellonella haemocytes recognized infective juveniles of Heterorhabditis bacteriophora; however, S. carpocapsae and Steinernema glaseri were not recognized. We provide experimental evidence that the purified trypsin has the potential to alter host haemocytes, actin filaments and to inhibit host haemolymph melanization.

Purification, biochemical and molecular analysis of a chymotrypsin protease with prophenoloxidase suppression activity from the entomopathogenic nematode Steinernema carpocapsae

A chymotrypsin serine protease (designated Sc-CHYM) was purified by gel filtration and anion-exchange chromatography from excretory-secretory products of parasitic stage Steinernema carpocapsae. The purified protease had an apparent molecular mass of 30kDa and displayed a pI of 5.9. This protease demonstrated high activity against the chymotrypsin-specific substrate N-Succinyl-Ala-Ala-Pro-Phe-p-nitroanilide and was highly sensitive to the inhibitor aprotinin. This protease digested the chromogenic substrate N-Succinyl-Ala-Ala-Pro-Phe-p-nitroanilide with K(m), V(max) and k(cat) values of 409microM/min, 0.389microM/min and 24.9s(-1), respectively. The protease was most active at pH 8.0 and 35 degrees C, and its proteolytic activity was almost completely reduced after incubation at 75 degrees C for 30min. In vitro, this enzyme suppressed prophenoloxidase activity. In vivo, demonstration of encapsulation and melanization by purified chymotrypsin imbibed beads showed it could prevent hemocyte encapsulation and melanization by 12 and 24h, respectively. Sequence comparison and evolutionary marker analysis showed that the putative protein was a chymotrypsin-like protease with potential degradative, developmental and fibrinolytic functions. Expression pattern analysis revealed that the gene expression of Sc-CHYM was up-regulated in the parasitic stage. Sc-CHYM was clustered with several insect chymotrypsins and formed an ancestral branch in the phylogenetic tree, suggesting that Sc-CHYM branched off at an early stage of cluster divergence. The results of this study suggest that Sc-CHYM is a new member of the chymotrypsin serine protease family and that it might act as a virulence factor in host-parasite interactions.

Purification and characterization of a leucine aminopeptidase from the bovine filarial parasite Setaria cervi

Using synthetic peptide substrate Leu-p-NA, leucine aminopeptidase (LAP) activity was detected in both microfilarial and adult stages of a bovine filarial parasite Setaria cervi. A single protein fraction containing LAP activity was purified from the adult female S. cervi using three different chromatographic techniques. This purified enzyme was shown to be a 321 kDa zinc dependent metalloexopeptidase having maximum activity at pH 9.0 and 37 degrees C. Its activity was significantly inhibited by aminopeptidase specific inhibitors such as 1,10-phenanthroline, ethylene diaminetetraacetic acid (EDTA), amastatin and bestatin; and activated by Co2+, Mn2+ and Mg2+ ions. Puromycin and l-amino acids (e.g., glutamine, leucine and glycine) also showed some moderate inhibitory effects on the purified enzyme. Among various synthetic substrates tested, the purified enzyme hydrolysed Leu-p-NA at very high rate suggesting it to be a LAP. Both ELISA and western blotting analyses of S. cervi LAP revealed the presence of homologous protein in human filarial parasite Wuchereria bancrofti. The higher sensitivity of S. cervi LAP with microfilariaemic sera compared to other categories of W. bancrofti infected human sera implied its potential as a serodiagnostic marker against active filarial infection. The antigenic similarity between S. cervi LAP and W. bancrofti makes this molecule ideal for the discovery of new diagnostic marker, drugs and/or vaccine candidate for human lymphatic filariasis.

Tissue localization of collagenase and leucine aminopeptidase in the bovine filarial parasite Setaria cervi

BACKGROUND

Like other helminth proteases, filarial proteases have also been shown to require for parasite survival inside the host and mediate various physiologic processes such as tissue invasion, feeding, embryogenesis and host immune evasion. Many of these proteases have shown potential for vaccines and chemotherapeutic agents against active filarial infections. Setaria cervi is a bovine filarial parasite and serves as a good parasite model for the studies in lymphatic filariasis. Recently, a 175 kDa collagenase and leucine aminopeptidase (LAP) have been purified and characterized from the bovine filarial parasite S. cervi and shown to be potential vaccine candidate and diagnostic marker, respectively for human lymphatic filariasis. However, their tissue localizations and putative roles in the parasite biology have not yet been examined and thus remain unclear. Therefore, the current study attempts to localize and explore the putative roles of these two enzymes in S. cervi.

METHODS

The tissue distributions of 175 kDa collagenase and leucine aminopeptidase in S. cervi were examined by immunohistochemical and histochemical methods, respectively. Immune sera obtained from the jirds immunized with collagenase served as primary antibody, rabbit anti-mouse IgG-HRP conjugate as secondary antibody and DAB as the substrate for the immunostaining of collagenase. Leu-betaNA was used as the substrate for the histochemical staining of LAP.

RESULTS

Both the collagenase and LAP were present in the body wall; however, they differ in their distribution pattern in different layers of body wall. Collagenase was mainly localized in epicuticle, cuticle, syncytial hypodermis and the nerve cord region whereas LAP was more concentrated in epicuticle, longitudinal muscle layers and almost absent or very faintly stained in syncytial hypodermis and nerve cord region. Both collagenase and LAP showed their common distributions in intestine, uterus and mature eggs, growing embryos and mf. Very strong immunostaining of collagenase in the outer body surface of the parasite indicates its major role in host-parasite relationship whereas the presence of LAP in muscular region suggests its role in tissue remodeling. The common presences of collagenase and LAP in the S. cervi intestine, ovary, uterus, eggs and mf suggest that they also have collaborative roles in molting, nutrition and embryogenesis. The data obtained on their immunological characterizations and their presence in important parasite organs give strong indication that they are critical for the survival of filarial parasite and thus can be good vaccine candidates and/or diagnostic markers for human lymphatic filariasis.

CONCLUSION

The manuscript reports for the first time the tissue distribution of collagenase and LAP in the bovine filarial parasite S. cervi and discuss their putative roles in vivo. Our findings also open the avenue to examine the roles of these two proteases in vivo, which will require further experiments like using their natural substrates and/or specific inhibitors in each tissues.

Partial purification and characterization of an aminopeptidase from Eimeria tenella

Our previous investigation demonstrated the expression in Eimeria tenella sporulated oocysts of an aminopeptidase (AP) with strong homology to AP N. To further understand the role of proteases during development, we investigated the molecular and biochemical properties of E. tenella AP. Greater than 95% AP activity was present in a soluble extract during sporulation of oocysts with highest activity in fully sporulated oocysts. The AP activity was inhibited by the AP inhibitors bestatin and 1,6-phenanthroline, but not by serine protease inhibitors. The AP had specificity for synthetic endopeptidase substrates that contain arginine, alanine, or glycine at the N terminus. Partial purification of the enzyme yielded a major protein band with an Mr of about 106 kDa and an isoelectric point (Ip) of 5.1. Reverse transcription-polymerase chain reaction indicated that the gene for AP is expressed during sporulation, but expression is absent or greatly reduced in the sporozoites and merozoites. On the basis of the deduced gene structure, the predicted Mr is 110 kDa with a pI of 5.59. Database search indicates that the E. tenella AP shares significant homology with the AP from Apicomplexan taxa: Toxoplasma gondii, Cryptosporidium parvum, and Cryptosporidium hominis. Together, these results confirm the presence of a cytosolic AP related to AP N, which is expressed and active during sporulation of E. tenella oocysts.

Cloning and characterisation of an aspartyl protease inhibitor (API-1) from Ancylostoma hookworms

Hookworm infection persists as a public health problem in developing nations. Vaccine-based strategies offer the best chance of long-term control. Aspartyl protease inhibitors from parasitic nematodes are highly immunogenic, and have been suggested as potential vaccine antigens. An aspartyl protease inhibitor, API-1, was cloned and characterised from the hookworms Ancylostoma caninum and Ancylostoma ceylanicum. Using sequence from the hookworm expressed sequence tag project, specific primers were designed and used to amplify Ac-api-1 from A. caninum infective L3 cDNA by PCR. Amplicons from the 5' and 3' ends were cloned, sequenced, and combined to create an 874-bp full-length composite sequence of the Ac-api-1 gene. The A. ceylanicum api-1 cDNA of 878 bp was cloned from L3 cDNA using the A. caninum primers. The amino acid sequences of hookworm orthologues were nearly identical, and database searching indicated they belonged to the aspin family, a group of nematode specific aspartyl protease inhibitors that includes the Ascaris pepsin inhibitor PI-3. Ac-api-1 mRNA was detected by reverse transcriptase PCR in eggs, L1, L3 and adult life cycle stages. A polyclonal antiserum against Escherichia coli expressed recombinant Ac-API-1 detected the protein in adult A. caninum excretory/secretory products, but not in those from activated infective larvae. Immunolocalisation experiments using the antiserum indicated that Ac-API-1 is present primarily in the pseudocoelomic fluid in adult hookworms. Soluble, yeast-expressed Ac-API-1 failed to inhibit pepsin or a hookworm gut aspartyl protease in vitro, but inhibited approximately 30% of the proteolytic activity of adult excretory/secretory products. The pseudocoleomic location, presence in all life cycle stages, lack of inhibitory activity against pepsin, and inhibitory activity against excretory/secretory products suggest that Ac-API-1 inhibits an unidentified, putative aspartyl protease secreted by adult hookworms, and may be released as an enzyme-inhibitor complex. The highly immunogenic properties of nematode aspins suggest that Ac-API-1 represents a promising target for a recombinant hookworm vaccine.

Leucine aminopeptidase of the human blood flukes, Schistosoma mansoni and Schistosoma japonicum

An array of schistosome endoproteases involved in the digestion of host hemoglobin to absorbable peptides has been described, but the exoprotease responsible for catabolising these peptides to amino acids has yet to be identified. By searching the public databases we found that Schistosoma mansoni and Schistosoma japonicum express a gene encoding a member of the M17 family of leucine aminopeptidases (LAPs). A functional recombinant S. mansoni LAP produced in insect cells shared biochemical properties, including pH optimum for activity, substrate specificity and reliance on metal cations for activity, with the major aminopeptidase activity in soluble extracts of adult worms. The pH range in which the enzyme functions and the lack of a signal peptide indicate that the enzyme functions intracellularly. Immunolocalisation studies showed that the S. mansoni LAP is synthesised in the gastrodermal cells surrounding the gut lumen. Accordingly, we propose that peptides generated in the lumen of the schistosome gut are absorbed into the gastrodermal cells and are cleaved by LAP to free amino acids before being distributed to the internal tissues of the parasite. Since LAP was also localised to the surface tegument it may play an additional role in surface membrane re-modelling.

Opiate alkaloids and nitric oxide production in the nematode Ascaris suum

The tissue distribution, course of secretion, and sex differences of morphine were delineated in Ascaris suum. Nitric oxide (NO) release in various tissues in response to morphine and its metabolite morphine-6-glucuronide (M6G) were also examined. Ascaris suum of both sexes along with their incubation fluid were analyzed for morphine concentrations by high-performance liquid chromatography (HPLC) over a 5-day period. Various tissues were also dissected for HPLC and NO analysis. Morphine was found to be most prevalent in the muscle tissue, and there is significantly more morphine in females than males, probably because of the large amounts present in the female uterus. Morphine (10(-9) M) and M6G (10(-9) M) stimulated the release of NO from muscles. Naloxone (10(-7) M) and N-nitro-L-arginine methyl ester (10(-6) M) blocked (P < 0.005) morphine-stimulated NO release from A. suum muscle tissue. D-Phe-Cys-Tyr-D-Trp-Om-Thr-Pen-Thr-NH2 (CTOP) (10(-7) M) did not block morphine's NO release. However, naloxone could not block M6G-stimulated NO release by muscles, whereas CTOP (10(-7) M) blocked its release. These findings were in seeming contradiction to our earlier inability to isolate a mu opiate receptor messenger RNA by reverse transcriptase-polymerase chain reaction using a human mu primer. This suggests that a novel mu opiate receptor was possibly present and selective toward M6G.

Characterization of aminopeptidase activity from three species of microsporidia: Encephalitozoon cuniculi, Encephalitozoon hellem, and Vittaforma corneae

Microsporidia are obligate intracellular parasites of the phylum Microspora. To date, more than 1,200 species within 144 genera have been described, with 14 infecting humans. Currently, no effective treatment exists for human microsporidiosis. In this study, the biochemical properties of the aminopeptidases were investigated within several species of microsporidia. Aminopeptidase activity was detected in 3 species of microsporidia, Encephalitozoon cuniculi, E. hellem, and Vittaforma corneae, using a fluorometric substrate assay. Each species exhibited distinct aminopeptidase properties. The cytosolic neutral aminopeptidase activities of the Encephalitozoon spp. were characterized as preferentially cleaving leucine, whereas those of V. corneae cleaved arginine. Native polyacrylamide gel electrophoresis estimated the molecular mass of E. cuniculi, E. hellem, and V. corneae as 74, 72, and 79 kDa, respectively. Enzymatic activity was inhibited by bestatin and it's analogue, nitrobestatin, indicating that the enzyme was an aminopeptidase for all species. Inhibition with the chelating agents ethylenediaminetetraacetic acid and 1,10phenanthroline characterized the enzymes as metalloaminopeptidases. Subcellular fractionation of the 3 microsporidial species suggested that the enzyme activity was localized in the cytosolic fraction. Optimal enzyme activity was observed at pH 7.2 for all species. This is the first report of enzyme characterization from these 3 species of microsporidia.