Development of a pathogenesis-based therapy for peeling skin syndrome type 1

BACKGROUND

Peeling skin syndrome type 1 (PSS1) is a rare and severe autosomal recessive form of congenital ichthyosis. Patients are affected by pronounced erythroderma accompanied by pruritus and superficial generalized peeling of the skin. The disease is caused by nonsense mutations or complete deletion of the CDSN gene encoding for corneodesmosin (CDSN). PSS1 severely impairs quality of life and therapeutic approaches are totally unsatisfactory.

OBJECTIVES

The objective of this study was to develop the first steps towards a specific protein replacement therapy for CDSN deficiency. Using this approach, we aimed to restore the lack of CDSN and improve cell-cell cohesion in the transition area of the stratum granulosum (SG) to the stratum corneum.

METHODS

Human CDSN was recombinantly expressed in Escherichia coli. A liposome-based carrier system, prepared with a cationic lipopeptide to mediate the transport to the outer membrane of keratinocytes, was developed. This formulation was chosen for CDSN delivery into the skin. The liposomal carrier system was characterized with respect to size, stability and toxicity. Furthermore, the interaction with primary keratinocytes and human epidermal equivalents was investigated.

RESULTS

The liposomes showed an accumulation at the membranes of keratinocytes. CDSN-deficient epidermal equivalents that were treated with liposomal encapsulated CDSN demonstrated presence of CDSN in the SG. Finally, the penetration assay and histological examinations revealed an improved epidermal integrity for CDSN-deficient epidermal equivalents, if they were treated with liposomal encapsulated CDSN.

CONCLUSIONS

This study presents the first preclinical in vitro experiments for a future specific protein replacement therapy for patients affected by PSS1.

LEKTI domains D6, D7 and D8+9 serve as substrates for transglutaminase 1: implications for targeted therapy of Netherton syndrome

BACKGROUND

Transglutaminase (TG)1 plays a key role in the formation of the cornified envelope and thus in the maintenance of the epidermal barrier. Patients with Netherton syndrome (LEKTI deficiency) have increased activity of both TG1 and serin proteases.

OBJECTIVES

To determine whether there is a functional biochemical link between TG1 and LEKTI and whether LEKTI domains could possibly serve as substrates for TG1.

METHODS

We analysed the protein sequence of LEKTI for possible TG1 recognition sites using bioinformatics. Synthetic peptides and recombinant LEKTI domains D6, D7 and D8+9 were examined in vitro and in situ for possible substrate specificity. The recombinant LEKTI domains were studied for inhibitory activity in a kallikrein (KLK)5 activity test.

RESULTS

We identified possible TG1 consensus sequences in LEKTI domains D6, D7 and D8+9, pointing to a novel biological link between these two proteins. Indeed, synthesized short peptides from these consensus sequences were incorporated into the TG1 activity zone of the epidermis. In vitro the entire recombinant domains of LEKTI showed substrate specificity for TG1, which was again confirmed in situ. The inhibitory activity of the recombinant LEKTI domains was confirmed by a KLK5 inhibition test. The strongest inhibition was observed for domains D8+9.

CONCLUSIONS

There are specific domains of LEKTI that are recognized and processed by TG1. LEKTI domains D6, D7 and D8+9 contribute to the formation and protection of the cornified envelope. These results impact the development of protein replacement therapy approaches for Netherton syndrome. What's already known about this topic? LEKTI and transglutaminase (TG)1 are key proteins involved in the terminal differentiation of the epidermis. Lack of LEKTI causes Netherton syndrome; TG1 deficiency causes lamellar ichthyosis. The serine protease inhibitor LEKTI is processed into different functional units. Among different target proteases, kallikrein (KLK)5 appears to be a key player in disease pathology. It has been demonstrated that LEKTI domain 6 inhibits KLK5 and KLK7; LEKTI domains 8-11 also inhibit KLK14. What does this study add? The single LEKTI domains 6, 7 and the functional unit of domains 8 and 9 contain recognition motifs for TG1. We show that these domains and unit are crosslinked into the epidermis by TG1. Functional analyses of the recombinant LEKTI domains revealed that LEKTI D8+9 has the strongest inhibitory effect on KLK5. What is the translational message? The novel functional link between LEKTI and TG1 should be taken into account when considering the development of a targeted topical protein therapy for Netherton syndrome. The unit of domains D8+9 may be sufficient for this purpose.

Comparative characterization of two galectins excreted-secreted from intestine-dwelling parasitic versus free-living females of the soil-transmitted nematode Strongyloides

Helminths are complex pathogens that ensure their long-term survival by influencing the immune responses of their host. Excretory/secretory products (ESP) can exert immunoregulatory effects which foster parasite survival. Galectins represent a widespread group of β-galactoside-binding proteins which are involved in a multitude of biological processes operative in parasite-host interaction. We had earlier identified seven galectins in Strongyloides ratti, four of them detected in the ESP of distinct developmental stages of the parasite. In the present report, we focused on the characterization of two of them, Sr-galectin-1 (Sr-Gal-1) and Sr-galectin-3 (Sr-Gal-3). While Sr-Gal-3 expression was strongest in parasitic females, Sr-Gal-1 was predominantly expressed in free-living females. Both proteins were cloned and recombinantly expressed in an E. coli expression system. Their glycan-binding activity was verified by haemagglutination and glycan array analysis. Furthermore, primary immunological activities of the Sr-galectins were initially investigated by the application of an in vitro mucosal 3D-culture model, comprising of mucosa-associated epithelial and dendritic cells. The Sr-galectins stimulated preferentially the release of the type 2 cytokines thymic stromal lymphopoietin and IL-22, a first indication for immunoregulatory activity. In addition, the Sr-galectins dose-dependently fostered cell migration. Our results confirm the importance of these carbohydrate-binding proteins in host-parasite-interaction by indicating possible interaction with the host mucosa-associated cells.

Medicinal plant extracts and plant-derived polyphenols with anthelmintic activity against intestinal nematodes

Covering: 2001 up to the end of 2016Polyphenols comprise a structurally diverse class of natural products. As the development of new anthelmintic drugs against soil-transmitted helminthiases is an urgent need and polyphenols are widely used in the treatment of nematode infections in traditional medicine and modern science, we summarize the state of knowledge in the period of mainly 2001 up to the end of 2016 on plant extracts with known polyphenolic composition and of defined polyphenols, mainly from the classes of condensed and hydrolysable tannins, flavonoids, and phenylpropanoids. The diverse biological activity against different helminths and the underlying mechanisms are reviewed.

Crystallization of the major cytosolic glutathioneS-transferase fromOnchocerca volvulus

Glutathione S-transferases (GSTs) are a family of detoxification enzymes that catalyse the conjugation of glutathione to xenobiotic and endogenous electrophilic compounds, thus facilitating their elimination from cells. The recombinant Onchocerca volvulus GST2 has been expressed in Escherichia coli, purified and crystallized by the hanging-drop vapour-diffusion technique. Two different crystal forms were grown under identical conditions. They belong to space groups P2(1)2(1)2 and P2(1), respectively. The unit-cell parameters obtained are a = 112.6, b = 84.3, c = 45.1 A for the P2(1)2(1)2 crystal form and a = 51.6, b = 82.3, c = 56.7 A, beta = 95.89 degrees for the P2(1) form. Complete data sets to 2.6 and 1.5 A, respectively, have been collected at 100 K with synchrotron radiation.

Crystallization and preliminary X-ray diffraction studies of the glutathione S-transferase from Plasmodium falciparum

Glutathione S-transferases (GSTs) belong to a family of detoxification enzymes that conjugate glutathione to various xenobiotics, thus facilitating their expulsion from the cells. For high-resolution crystallographic investigations, GST from the human malarial parasite Plasmodium falciparum was overexpressed in bacterial cells and crystallized using hanging-drop vapour diffusion. X-ray intensity data to 2.8 A resolution were collected from an orthorhombic crystal form with unit-cell parameters a = 62.2, b = 88.3, c = 75.3 A. A search for heavy-atom derivatives has been initiated, along with phase-determination efforts by molecular replacement.

PCR-based detection and identification of the filarial parasite Brugia timori from Alor Island, Indonesia

Brugia timori is widely distributed on Alor Island, Indonesia, where it causes a high degree of morbidity. The HhaI tandem repeat of B. timori was found to be identical to that of B. malayi, for which sensitive PCR-based assays have already been developed. Using one of these assays, a single microfilaria (mf) of B. timori, present in a spot of dry blood on filter paper, could be detected. The assay was equally sensitive in the detection of B. timori and B. malayi. When the collected mosquitoes were pooled according to species and tested with the assay, 39 (64%) of the 61 Anopheles barbirostris pools (containing a total of 642 mosquitoes) were positive. As none of the 33 Culex pools tested (which contained 624 mosquitoes) gave a positive result, and An. barbirostris is the only Anopheles species commonly caught on human bait in Alor, An. barbirostris is assumed to be the main and perhaps only local vector. Brugia timori could be differentiated from B. malayi by restriction-endonuclease digestion of the PCR-amplified mitochondrial cytochrome oxidase subunit 2. A few distinct nucleotide exchanges were also found in the second internal transcribed ribosomal spacer of the filariae, and in the 16S rDNA and FTSZ gene of their Wolbachia endobacteria. The results show that B. timori can be effectively detected using the PCR-based assay developed for B. malayi and can then be differentiated from B. malayi by other molecular markers. PCR-based techniques targeting the HhaI repeat can therefore be employed for monitoring B. timori in the framework of the Global Programme to Eliminate Lymphatic Filariasis.

An internal control for the detection of Onchocerca volvulus DNA by PCR-ELISA and rapid detection of specific PCR products by DNA Detection Test Strips

We developed a polymerase chain reaction-enzyme-linked immunosorbent assay (PCR-ELISA) for the detection of Onchocerca volvulus DNA. To standardize the PCR and to avoid false-negative results, an internal control DNA was co-amplified by the same set of primers. We differentiated the wild-type PCR product of the O-150 DNA sequence from the internal control by specific DNA probes. Detection of biotinylated PCR products by DNA probes was performed by ELISA to quantify the PCR product or by DNA Detection Test Strips as a rapid field technique. The methods were evaluated on skin biopsies from individuals living in an area endemic for O. volvulus in Uganda, but with low microfilaria densities because of ivermectin treatment. Microfilaria density was assessed by a single skin snip and a second skin snip was examined by PCR. Among 69 samples from microfilaria carriers, 47 (68%) were positive by ELISA and 55 (80%) by test strip detection of PCR products. When 39 samples of microfilaria-negative individuals from the same area were tested, 10 (27%) were positive by ELISA and 12 (31%) by test strips. None of the 19 samples obtained from persons living in an area not endemic for O. volvulus but endemic for Mansonella streptocerca was positive in either test. Although the ELISA is theoretically more sensitive than the test strips for the detection of PCR products, examination of field samples revealed that the test strip method had a higher operational sensitivity and was more convenient to perform. Thus, the DNA Detection Test Strips are a rapid and low-tech tool for identification of PCR products in laboratories of countries endemic for onchocerciasis.

Structural analysis and antibody response to the extracellular glutathione S-transferases from Onchocerca volvulus

Onchocerca volvulus is a human pathogenic filarial parasite which, like other parasitic nematodes, is capable of surviving in an immunologically competent host by employing a variety of immune evasion strategies and defense mechanisms including the detoxification and repair mechanisms of the glutathione S-transferases (GSTs). In this study we analyzed the glycosylation pattern and the immunological properties of extracellular O. volvulus GST1a and -1b (OvGST1a and -1b). The enzymes differ in only 10 amino acids, and both are glycoproteins that have cleavable signal peptides and unusual N-terminal extensions. These characteristics have not been described for other GSTs so far. Mass spectrometry analyses indicate that both enzymes carry high-mannose type oligosaccharides on at least four glycosylation sites. Glycosylation sites 1 to 3 of OvGST1a (OvGST1b sites 2 to 4) are occupied by truncated N-glycans (Man(2)GlcNAc2 to Man(5)GlcNAc(2)), and N glycosylation site 4 of OvGST1a (OvGST1b site 5) carries Man(5)GlcNAc2 to Man(9)GlcNAc(2). To analyze the capacity of these secretory GSTs to stimulate host immune responses, we studied the antibody responses of onchocerciasis patients against the native affinity-purified OvGST1a and -1b. By enzyme-linked immunosorbent assay we showed that OvGST1a and -1b are immunodominant antigens, with less than 7% nonresponder patients. A direct comparison of the antibody responses to the glycosylated and deglycosylated forms demonstrates the high immunogenicity of the N-glycans. Analyses of the antibody responses to the unusual N-terminal extension show an enhanced recognition of this portion by patients as opposed to recognition of the recombinant protein without extension.

Gene structure of the extracellular glutathione S-transferase from Onchocerca volvulus and its overexpression and promoter analysis in transgenic Caenorhabditis elegans

Two highly similar genes encoding unique extracellular, glycosylated glutathione S-transferases (GSTs) of the human-pathogenic nematode, Onchocerca volvulus (Ov-GST1a and Ov-GST1b), have been isolated and characterised. The genes are approximately 3 kb in length and consist of seven exons interrupted by introns of approximately 100 bp in length, with the exception of intron II, which is approximately 1.6 kb in length. Interestingly, exon I and II encode a signal peptide and an N-terminal extension before sequence homology to other GSTs begins. The 5' flanking region was sequenced and analysed for transcription factor binding sites. Consistent with the lack of a TATA box, analysis of the mRNAs by primer extension showed multiple transcription start sites spread over a 60 bp region. To examine the activity and specificity of the Ov-GST1a gene promoter, we have exploited Caenorhabditis elegans as a heterologous transformation system. To analyse whether transgenic C. elegans are able to carry out processing and post-transcriptional modifications of the Ov-GST1a correctly, the protein was ectopically overexpressed in C. elegans. The parasite-derived Ov-GST1a gene product was correctly processed in transgenic C. elegans and posttranslational modifications, such as signal peptide cleavage and N-glycosylation, were performed successfully. This further demonstrates the potential of C. elegans as a host for expression of candidate vaccine antigens from O. volvulus and affirms the role of C. elegans as a model for parasitic nematodes.

A common class of nematode glutathione S-transferase (GST) revealed by the theoretical proteome of the model organism Caenorhabditis elegans

The genome verified C. elegans free-living nematode model is a new tool for investigating gene expression in human and animal nematode parasites. There is limited information on designating glutathione S-transferase (GST) to specific classes in lower invertebrates such as nematodes. Following cloning, amino acid sequence alignment, recombinant expression and Western blotting we provide evidence of a new GST class in nematodes or lower invertebrates.

A stress-responsive glyoxalase I from the parasitic nematode Onchocerca volvulus

Glyoxal, methylglyoxal and other physiological alpha-oxoaldehydes are formed by the lipid peroxidation, glycation and degradation of glycolytic intermediates. They are detoxified enzymically by the glyoxalase system. To investigate the physiological function of glyoxalase I in parasitic organisms, the cDNA for glyoxalase I from the filarial nematode Onchocerca volvulus (designated Ov-GloI) has been cloned and characterized. The isolated cDNA contains an open reading frame of 579 bp encoding a protein with a calculated molecular mass of 21930 Da. Owing to the high degree of sequence identity (60%) with human glyoxalase I, for which the X-ray structure is available, it has been possible to build a three-dimensional model of Ov-GloI. The modelled core of Ov-GloI is conserved compared with the human glyoxalase I; however, there are critical differences in the residues lining the hydrophobic substrate-binding pocket of Ov-GloI. A 22 kDa protein was obtained by heterologous expression in Escherichia coli. A homogeneous enzyme preparation was obtained by affinity purification and functional characterization of the recombinant enzyme included the determination of kinetic constants for methylglyoxal and phenylglyoxal as well as inhibition studies. Gel filtration demonstrated a dimeric structure. To assess the role of Ov-GloI as a potential vaccine candidate or serodiagnostic tool, the serological reactivity of the recombinant Ov-GloI was analysed with sera from microfilaria carriers and specific IgG1 antibodies were detected. The effects of oxidative insult, namely plumbagin and xanthine/xanthine oxidase, on the gene transcript level of Ov-GloI were investigated. By using a semi-quantitative PCR ELISA it was shown that Ov-GloI is expressed at elevated levels under conditions of oxidative stress.

The gamma-glutamylcysteine synthetase of Onchocerca volvulus

The tripeptide glutathione (GSH) plays an important role in the maintenance of the intracellular thiol redox state and in detoxification processes. The intracellular GSH level depends on glutathione reductase as well as on GSH synthesis. The first and rate limiting step in the synthetic pathway is catalysed by gamma-glutamylcysteine synthetase (gamma-GCS). The gamma-GCS was partially purified from the filarial parasite Onchocerca volvoulus and preliminary steady state kinetics were performed. The Ki-value for L-buthionine-S,R-sulphoximine (BSO), a specific inhibitor of gamma-GCS, was determined to be 0.13 microM, which is 54-fold lower than the Ki-value for the mammalian enzyme. Filarial gamma-GCS was also inhibited by cystamine with a Ki-value of 3.9 microM compared with 22.2 microM determined for the rat enzyme. Further, the cDNA and the gene of the O. volvulus gamma-GCS were cloned and sequenced. The gene of 5762 bp is composed of 14 exons and 13 introns. Southern blot analysis indicates that the gamma-GCS gene is present as a single-copy gene. In accordance with Northern blot analysis, the entire cDNA sequence encompasses 2377 bp. At its 5' end a nematode-specific spliced leader 130 bp upstream of the first in frame methionine was identified. The cDNA encodes a polypeptide of 652 amino acids with 50 and 69% sequence identity to the human and the Caenorhabditis elegans counterparts, respectively. The filarial gamma-GCS is proposed as a potential drug target.

Inhibition of glutathione S-transferases (GSTs) from parasitic nematodes by extracts from traditional Nigerian medicinal plants

Piliostigma thonningii, Ocimum gratissimum, Nauclea latifolia and Alstonia boonei are used in Nigerian traditional medicines against gastrointestinal helminths of animals and man. Proanthocyanidins were detected in Piliostigma and Nauclea, but not Alstonia or Ocimum. Extracts of these plants killed 50% of brine shrimp nauplii at <10 ppm (Nauclea), 100 ppm (Piliostigma) and <1000 ppm (Ocimum and Alstonia), the Nauclea LD50 being similar to the anthelmintic drug piperazine. Extracts were also toxic to the parasitic nematode Haemonchus infective L3 stage. Nematode glutathione-S-transferases (GSTs) are potential drug targets. Apart from Alstonia all the medicinal plants contained heat-stable inhibitory activities against recombinant Ascaris and Onchocerca GSTs in vitro. Piliostigma, Ocimum and Nauclea had IC50s of 2, 10 and 15 microg/mL respectively for Ascaris GST and 4, 8, 28 microg/mL respectively for Onchocerca GST. We suggest that the inhibitory properties of some of these Nigerian plant extracts against GST may contribute to the pharmacological basis of their efficacy against helminths in traditional herbal use.

Identification of a stress-responsive Onchocerca volvulus glutathione S-transferase (Ov-GST-3) by RT-PCR differential display

The effects of oxidative insult on gene transcript levels in the filarial nematode Onchocerca volvulus were investigated using differential display RT-PCR. Oxidative stress was applied with the reagents paraquat, plumbagin and xanthine-xanthine oxidase. In all three cases, a cDNA fragment encoding a novel glutathione S-transferase (GST) resembling members of the theta-class was identified as upregulated (PQ29, PG112, XOD26). The subsequently isolated full-length cDNA harbors a 753-bp open reading frame encoding a GST with 268 amino acid residues and a predicted molecular mass of 31 kDa. This stress-responsive GST (Ov-GST-3) possesses only 14 and 21% sequence identity with the other O. volvulus GSTs (Ov-GST-1 and Ov-GST-2, respectively). Interestingly, Ov-GST-3 shares higher sequence identity with GSTs that are upregulated due to environmental stress. In order to confirm the specific upregulation of the Ov-GST-3 transcripts identified by differential display and to analyze the mRNA levels of the other Ov-GSTs (Ov-GST-1 and Ov-GST-2) under elevated stress conditions, a semi-quantitative polymerase chain reaction-enzyme-linked immunosorbent assay was performed. The Ov-GST-3 gene transcript level increased dramatically in response to xanthine-xanthine oxidase and to a lesser extent with paraquat and plumbagin. In contrast, Ov-GST-1 and Ov-GST-2 did not show any significant alterations in their steady-state mRNA levels in response to oxidative stress when examining the same mRNA samples. The present study clearly demonstrates that Ov-GST-3 is a critical enzyme in the defense against oxidative stress.

Beta-carbonyl substituted glutathione conjugates as inhibitors Of O. volvulus GST2

A series of beta-carbonyl substituted glutathione conjugates were prepared and evaluated as inhibitors of OvGST2. Their specificity for the parasite derived protein was assessed through comparison with their inhibition of human piGST. Inhibition of OvGST2 has been demonstrated at low micromolar concentrations for these conjugates and selectivity for OvGST2 over human pi-GST of greater than 10-fold has been achieved.

Primary sequence and activity analyses of a catalase from Ascaris suum

A complete cDNA encoding the catalase (EC 1.11.1.6) has been isolated from the parasitic nematode Ascaris suum (AsCAT). The active-site residues, the residues involved in ligand interaction, and NADPH-binding residues of the bovine liver catalase-type enzyme are highly conserved in the AsCAT predicted amino acid sequence. To confirm that the AsCAT cDNA encodes a functional enzyme, active recombinant protein (rAsCAT) was produced in a procaryotic expression system. The subunit molecular mass of the purified recombinant protein (rAsCAT) was determined to be approximately 60 kDa. According to gel filtration, the molecular mass of the active enzyme is 240 kDa, indicating that the catalase subunits form a homotetramer in solution. The optical spectrum of rAsCAT shows a typical ferric haem spectrum with a Soret band at 407 nm. Fluorescence spectroscopy demonstrates that rAsCAT binds NADPH. rAsCAT has catalase activity with hydrogen peroxide over a broad pH range, with a specific activity of 37,800 U mg-1. In addition to its catalase activity, rAsCAT displays peroxidase activity using the substrates t-butyl hydroperoxide and o-dianisidine. The haem ligands NaN3 and KCN caused a 50% inhibition of catalase activity at 9 and 19 microM, respectively. In the presence of a H2O2-generating system, catalase activity of rAsCAT was inhibited by 3-aminotriazole, phenolic compounds, and drugs.

Onchocerca volvulus: ultrastructural localization of two glutathione S-transferases

Glutathione S-transferases (GSTs) are essential detoxification enzymes for virtually all cells and may additionally aid in parasite survival by counteracting host-induced damage. GSTs from parasitic nematodes have been identified as potential targets for both immuno- and chemotherapy. To more closely characterize a 31-kDa (OvGST1) and a 24.5-kDa (OvGST2) GST from the pathogenic human filarial parasite Onchocerca volvulus, immunolocalization by electron microscopy was performed using two distinct affinity-purified polyclonal antisera raised against the recombinant OvGST1 and OvGST2. The strongest immunogold staining for OvGST1 was identified in the body wall of adult worms, especially in protuberances of the cuticle which lie in pouches of the hypodermis and in the outer zone of the syncytial hypodermis, where the external plasma membrane forms series of lamellae. Gold particles were also observed on the epicuticle of the adults and in the region of the border between the cuticle and hypodermis of microfilariae. The larval stages L1, L2, and infective L3 were also immunopositive for OvGST1. There was no specific labeling in the longitudinal musculature, the intestine, or the uterine wall of the adult worm. In contrast to the results for OvGST1, immunogold labeling for OvGST2 was observed throughout the whole hypodermal cytoplasm. The epithelial cells of the uterine wall showed moderate labeling. These ultrastructural immunolocalization results are consistent with the molecular characterization of both enzymes, indicating that OvGST1 is secreted out of the hypodermis into the cuticle and is acting at the host-parasite interface, while OvGST2 functions as an intracellular cytosolic housekeeping enzyme.

Characterization of human immune responses to the cytosolic superoxide dismutase and glutathione S-transferase from Onchocerca volvulus

In onchocerciasis patients and in O. volvulus-exposed individuals without signs of onchocericiasis, T- and B-cell responses to two recombinantly expressed O. volvulus enzymes were analysed and compared to responses to total protein extract of adult parasites. The cytosolic enzymes Cu/Zn superoxide dismutase 1 (OvSOD1) and glutathione S-transferase 2 (OvGST2) represent 2 detoxifying molecules which may play an important role in parasite defense against host-induced oxidative stress. The T-cell response to the two recombinant proteins was analysed by investigating the cytokine responses of peripheral blood mononuclear cells. Induction of IL-5 at the mRNA level and IL-5 and IL-10 at the protein level was demonstrated in patients with the generalized form of onchocerciasis and endemic normals without clinical manifestations. IFN-gamma was not found to be induced by either antigen. This pattern of lymphokine expression is indicative of a Th2-type response. Compared to patients with the generalized form, a higher level of cytokine induction was observed in the group of endemic normals. Low but significant IgG levels were observed against OvSOD1 in patients with onchocerciasis; higher antibody levels were found against OvGST2 in patients and endemic normals. The highest IgG levels were detected against the crude O. volvulus extract. These results indicate that the two recombinant O. volvulus proteins induce moderate T and B cell responses.

pOVEX vector: prokaryotic expression and purification of onchocerciasis vaccine candidate antigens as fusion proteins with the 24 kD Onchocerca volvulus glutathione S-transferase

An expression vector, pOVEX, has been designed and constructed, combining the advantages of the expression vectors pGEX-3X and pJC2o. The pOVEX vector produces a fusion protein with the 24 kD Onchocerca volvulus glutathione S-transferase (OvGST2) which is easy to purify in one step from bacterial extracts under non-denaturing conditions using glutathione-sepharose chromatography. High yields of fusion protein were produced from this T7 RNA polymerase-dependent expression vector, which were then cleaved by digestion with the factor Xa protease to separate the OVGST2 polypeptide from the expressed protein of interest. This vector will be particularly useful to O. volvulus investigators for the production of O. volvulus antigens for the analyses of host humoral and cellular responses to these proteins and for immunization studies.

Structural and functional analysis of a glutathione S-transferase from Ascaris suum

A recombinant glutathione S-transferase (GST) (EC 2.5.1.18) from the parasitic nematode Ascaris suum (AsGST1) displays specific activity with a variety of model substrates and secondary products of lipid peroxidation. The AsGST1 interacts with a range of model inhibitors, haematin-related compounds, bile acids and anthelminthics. The reported variations in biochemical activity correlate with structural differences observed by homology modelling. Here, differences in the topography of the proposed substrate binding site between the AsGST1 and the host GSTs were identified. A rabbit polyclonal antiserum was raised against the glutathione-binding proteins of A. suum and specific antibodies against AsGST1 were affinity-purified using the recombinant protein. These antibodies were used to localize the AsGST1 in adult worms by immunohistochemical staining. The strongest immunostaining for AsGST1 was localized in the intestine in all worms examined. This suggests that the enzyme may be responsible for the metabolism of materials that are incorporated from the environment, as well as for molecules that are excreted or secreted from the parasite to the environment. It also demonstrates the accessibility of the enzyme to an inhibitor or blocking antibody. In addition, the structure and sequence of the gene encoding AsGST1 have been determined. Southern-blot analyses of the AsGST1 gene suggests that it is a single-copy gene. The nucleotide sequence analysis revealed that the gene is composed of four exons and three introns, and potential regulatory elements were identified in the 5' flanking sequence.

Biochemical analysis, gene structure and localization of the 24 kDa glutathione S-transferase from Onchocerca volvulus

Survival of Onchocerca volvulus, a pathogenic human filarial parasite, is likely to depend upon the detoxification activities of the glutathione S-transferases (GSTs). The 24 kDa O. volvulus GST, OvGST2, was expressed in a bacterial system and the recombinant protein was purified to homogeneity by affinity chromatography. Specific activities of the recombinant OvGST2 (rOvGST2) with a variety of substrates, and in the presence of inhibitors, were determined. With the universal substrate 1-chloro-2,4-dinitrobenzene, the specific activity of rOvGST2 was 2130 nmol min-1 mg-1. The rOvGST2 showed relatively limited selenium-independent glutathione peroxidase activity, but secondary products of lipid peroxidation, namely members of the trans,trans-alka-2,4-dienal,trans-alk-2-enal and 4-hydroxyalk-2-enal series, were conjugated to glutathione via OvGST2 dependent activity. The gene encoding the OvGST2 was isolated and the nucleotide sequence determined. The ovgst2 gene was found to possess seven exons with six intervening sequences, with all except one having consensus splice-site junctions. This intron/exon organisation of the ovgst2 gene is almost identical with those described for the mammalian Pi class GST genes, consistent with the protein structural evidence that the OvGST2 is related to the Pi class GSTs. Southern blot analysis with total parasite genomic DNA indicated a single copy gene, with a restriction pattern consistent with that of the isolated gene. The tissue distribution of the OvGST2 was examined in O. volvulus by immunohistochemistry and was shown to be distinct from that of the OvGST1. The OvGST2 was located throughout the syncytial hypodermis of male and female adult worms, as well as in the uterine epithelium. Microfilariae, and infective third stage larvae of O. volvulus, isolated from Simulium neavei, were immunopositive for OvGST2.

Molecular cloning, expression and characterization of a recombinant glutathione S-transferase from Echinococcus multilocularis

We report the identification and characterization of the first cestode glutathione S-transferase (GST) cDNA sequence. A fragment of an Echinococcus multilocularis glutathione S-transferase cDNA was isolated by the polymerase chain reaction. Subsequently, a Lambda zap cDNA library prepared from mRNA from protoscolices of E. multilocularis was screened with this PCR fragment. A complete cDNA clone was isolated and the nucleotide sequence determined. Analysis of the E. multilocularis GST-deduced amino acid sequence indicates that it is clearly related to the mammalian mu-class GSTs. The E. multilocularis GST cDNA was expressed in Escherichia coli, using a protocol designed to produce the native enzyme rather than a fusion protein. The 25.5-kDa enzyme subunit was purified to homogeneity using glutathione-sepharose chromatography. Gel filtration demonstrated that this GST is enzymatically active as a homodimer. The recombinant enzyme had conjugating activity with organic hydroperoxides and with members of the trans,trans-2,4 alkadienal and trans-2-alkenal series, which are secondary products of lipid peroxidation.

A novel type of glutathione S-transferase in Onchocerca volvulus

Onchocerca volvulus is a pathogenic human filarial parasite which, like other helminth parasites, is capable of evading the host's immune responses by a variety of defense mechanisms which are likely to include the detoxification and repair mechanisms of the enzyme glutathione S-transferase (GST). In this study, we show that one of the previously described GSTs from O. volvulus appears to possess the characteristics of a secreted enzyme. When the complete O. volvulus GST1 (OvGST1) sequence presented here is compared with those of other GSTs, 50 additional residues at the N terminus are observed, the first 25 showing characteristics of a signal peptide. This is consistent with the N-terminal sequence data on the native mature enzyme which begins at amino acid 26, based on the deduced protein sequence from the cDNA. The native protein, without the signal peptide sequence, possesses a 24-amino-acid extension not present in other GSTs. The deduced amino acid sequence of the OvGST1 cDNA clone was shown to possess four potential N-glycosylation sites. Digestion of O. volvulus homogenate with endoglycosidase, followed by detection of OvGST1 with specific antibody, indicated that the enzyme possesses at least two N-linked oligosaccharide chains. Gel filtration of the Escherichia coli-produced recombinant OvGST1 showed that it is enzymatically active as a nonglycosylated dimer. OvGST1 is found in the media surrounding adult worms maintained in culture, indicating that, in vitro, this enzyme is released from the worm. The strongest immunostaining for OvGST1 was observed in the outer cellular covering of the adult worm body, the syncytial hypodermis, especially in the interchordal hypodermis, where the peripheral membrane forms a series of lamellae which run into the outer zone of the hypodermal cytoplasm.

Characterization of enzymatically active Onchocerca volvulus Cu/Zn superoxide dismutase expressed in Escherichia coli

The Onchocerca volvulus superoxide dismutase was expressed in Escherichia coli, using a protocol designed to produce the native enzyme rather than a fusion protein. The recombinant O. volvulus superoxide dismutase (rOVSOD) was found in the cytosol of the disrupted bacteria and represented > 10% of the total bacterial protein. The enzyme was purified to homogeneity using DEAE-Sepharose chromatography, followed by phenyl-Sepharose chromatography. The rOVSOD was enzymatically active which was demonstrated by its reactivity with O2.- produced either by the xanthine-xanthine oxidase system or by stimulated eosinophils. The specific activity was determined to be 4668 U mg-1. This activity could be blocked by rabbit antiserum raised against the rOVSOD. The maximal activity was obtained upon supplementation of the bacterial growth media and enzyme buffer with copper and zinc ions. Activity characteristics in the presence of inhibitors was also characteristic of a Cu/Zn superoxide dismutase. The rOVSOD has an apparent subunit molecular mass of 16,000 in SDS-PAGE. The active enzyme behaves as a dimer of 32 kDa as determined by gel filtration.

The Onchocerca volvulus mRNAs for a hsp70, a collagen-like protein and a ribosomal protein possess a 5' spliced leader sequence

To detect and analyse Onchocerca volvulus mRNAs possessing a spliced leader (SL) sequence, a SL cDNA library was constructed from O. volvulus RNA using a PCR method. Three of the sixty cDNAs analysed displayed significant homology to a known sequence. These cDNAs encode a hsp70, a collagen-like protein and a 60S ribosomal protein. The remaining cDNAs analysed either encoded proteins with no apparent homology to known sequences or they appeared to be generated from RNAs with an internal SL and did not possess an open reading frame.

Characterization and molecular cloning of a Cu/Zn superoxide dismutase from the human parasite Onchocerca volvulus

Evidence suggests that the helminth antioxidant enzyme superoxide dismutase (SOD) may play a role in parasite's defense against the cellular immune mechanisms of the host. In order to investigate this for the human parasite Onchocerca volvulus, the enzyme activity was characterized, the release of SOD by the parasite was examined, and a complete cDNA encoding the O. volvulus SOD was identified. The SOD activity in adult O. volvulus was found to be 8.1 +/- 4.2 U/mg of protein. A Cu/Zn-containing enzyme was demonstrated by its sensitivity towards cyanide, azide, and hydrogen peroxide. Isoelectric focusing, combined with an enzyme activity assay, revealed two activities at pI 6.8 and 7.6, with both activities inhibited by KCN. Adult parasites, maintained in vitro, released SOD into the culture medium, which was detected by enzyme activity. In parallel, lactate production was measured to ensure the viability of the parasite. Oligonucleotides (based upon conserved sequences in the SOD genes of other organisms) and the polymerase chain reaction were used to identify a portion of the SOD gene from O. volvulus genomic DNA. A cDNA library was constructed in lambda unizapII and screened with the genomic polymerase chain reaction fragment. A complete cDNA encoding the Cu/Zn SOD was identified, and its nucleotide sequence was determined. Southern blot hybridization experiments indicated that the Cu/Zn SOD is encoded by a single-copy gene with at least one intron.