Characterization of Spirometra erinaceieuropaei Plerocercoid Cysteine Protease and Potential Application for Serodiagnosis of Sparganosis

Background

Sparganosis is a neglected but important food-borne parasitic zoonosis. Clinical diagnosis of sparganosis is difficult because there are no specific manifestations. ELISA using plerocercoid crude or excretory–secretory (ES) antigens has high sensitivity but has cross-reactions with other helminthiases. The aim of this study was to characterize Spirometra erinaceieuropaei cysteine protease (SeCP) and to evaluate its potential application for serodiagnosis of sparganosis.

Methodology/Principal Findings

The full length SeCP gene was cloned, and recombinant SeCP (rSeCP) was expressed and purified. Western blotting showed that rSeCP was recognized by the serum of sparganum-infected mice, and anti-rSeCP serum recognized the native SeCP protein of plerocercoid crude or ES antigens. Expression of SeCP was observed at plerocercoid stages but not at the adult and egg stages. Immunolocalization identified SeCP in plerocercoid tegument and parenchymal tissue. The rSeCP had CP activity, and the optimum pH and temperature were 5.5 and 37°C, respectively. Enzymatic activity was significantly inhibited by E-64. rSeCP functions to degrade different proteins and the function was inhibited by anti-rSeCP serum and E-64. Immunization of mice with rSeCP induced Th2-predominant immune responses and anti-rSeCP antibodies had the potential capabilities to kill plerocercoids in an ADCC assay. The sensitivity of rSeCP-ELISA and ES antigen ELISA was 100% when performed on sera of patients with sparganosis. The specificity of rSeCP-ELISA and ES antigen ELISA was 98.22% (166/169) and 87.57% (148/169), respectively (P<0.05).

Conclusions

The rSeCP had the CP enzymatic activity and SeCP seems to be important for the survival of plerocercoids in host. The rSeCP is a potential diagnostic antigen for sparganosis.

Sparganosis is a neglected tropical disease; its diagnosis is difficult and it is often misdiagnosed. ELISA using the crude or ES antigens of plerocercoids cross reacts with other helminthiases. Cysteine protease is a type of hydrolase and plays important roles in the development and survival of parasites; it has been used for diagnostic markers and vaccine targets for some parasitic diseases. In this study, a 36 kDa Spirometra erinaceieuropaei cysteine protease (SeCP) was expressed and purified. The results showed that SeCP was a plerocercoid stage-specific protein located in the teguments and parenchymal tissue. The rSeCP had cysteine protease activity and functioned to degrade host proteins. Vaccination of mice with rSeCP induced high levels of IgG1 and anti-rSeCP antibodies with the ability to kill plerocercoids in an ADCC assay. The rSeCP had a high sensitivity and specificity for detecting anti-plerocercoid antibodies, and could be used as a potential antigen for serodiagnosis of sparganosis.

IgG antibody responses in early experimental sparganosis and IgG subclass responses in human sparganosis

Antigenic components in the crude extracts of Spirometra mansoni plerocercoid were analyzed in early experimental infections and in IgG subclass observed in clinical sparganosis. By IgG immunoblot, sera obtained serially from experimental mice, fed 5 spargana each, were reacted with the crude extracts. Protein bands at 36-26 kDa and 103 kDa showed positive reactions since two weeks after infection. In a differential immunoblot, in which a monospecific antibody against sparganum chymase at 36 kDa was pre-treated, the reactions at 36-26 kDa disappeared, indicating that the sparganum chymase and its degradation products invoked IgG antibody reactions. When 69 patients sera of human sparganosis were examined for their IgG subclass responses, IgG4 levels showed the highest reaction which was followed by IgG1. The IgG4 antibody also reacted mainly with 36-31 kDa protease. These results indicate that 36 kDa chymase of S. mansoni plerocercoid is the main antigenic component inducing IgG antibody response in early stage of experimental sparganosis and for specific IgG subclass reactions in human sparganosis.

Localization of a 24-kDa collagenase in the Gymnorhynchus gigas plerocercoid

A 24-kDa collagenase was localized in the Gymnorhynchus gigas plerocercoid immunohistochemically by peroxidase complex staining using polyclonal antibodies from NMRI mouse sera immunized with purified enzyme. Immunoreactivity was determined at different parts of the body (scolex, vesicle and caudal region) and mainly localized in microtriches and parenchymal tissues of the scolex and vesicle. These results, along with the absence of the enzyme in the plerocercoid excretion-secretion products, suggest that the 24-kDa collagenase is produced by parenchymal cells in the anterior region and transported to the outer regions of the worm It is possible that the enzyme plays an important role in degrading parasite tissues during the moulting process.

A neutral cysteine protease of Spirometra mansoni plerocercoid invoking an IgE response

When crude extracts of Spirometra mansoni plerocercoid (sparganum) were analysed by SDS-polyacrylamide gel electrophoresis (PAGE)/immunoblot using patients' sera, IgE antibodies reacted specifically with 21, 27 and 53 kDa proteins. The 21 and 27 kDa proteins have been previously characterized as cysteine proteases. In this study, the 53 kDa protein was confirmed, by immunoprecipitation, to induce a specific IgE response. The protein was purified by affinity chromatography using an IgG1 (kappa 2) type mAb. The protein was partially sensitive to peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F (endo F) digestion. It exhibited an endoproteinase activity in a thiol-dependent manner preferentially degrading benzoyloxycarboxyl-phenylalanyl-arginyl-4- methoxy-beta-naphthylamide (Z-phe-arg-MNA) of a panel of substrates tested. This endoprotease activity was maximal at pH 6.5 and in 0.1 M sodium phosphate. The proteolytic activity was inhibited by 10(-5) M L-trans-epoxysuccinyl-L- leucylamido-(4-guanidino)butane (E-64) and 1 mM iodoacetamide (IAA), and potentiated by dithiothreitol (DTT, 5 mM).

[Localization and characteristics of lactate and malate dehydrogenase in the sparganum and adult worm of Spirometra erinacei]

This study investigated the enzyme histochemical localization and characteristics of lactate (LDH) and malate dehydrogenase (MDH) related with the oxidation-reduction metabolism in the sparganum and adult of S. erinacei. By enzyme histochemical assay, activity of LDH was strong in the tegument and subtegumental muscle layers of the adult and sparganum. Activity of MDH was strong in the tegument of the sparganum and subtegumental muscle layers of the adult. However it was weak in the tegument of the adult. By electrophoresis, 45 kDa band was major and common in LDH of adults and spargana. The 150 kDa molecule was the major and common band in MDH of adults and r-spargana (from experimentally infected rats). By isoelectrofocusing, isoelectric points (PI) of 4 MDH isozyme from adult worm were 6.0, 6.5, 6.7 and 7.1, respectively. PI 6.0 was the major band. The active range of pH for MDH was about pH 6 approximately 8 and the optimum pH was pH 7. The effective temperature on the MDH was about 30 degrees C approximately 50 degrees C and the optimum temperature was about 40 degrees C in spargana and adult worm. In the stability against heat, when MDH was heated at 85 degrees C for 10 seconds, the activity was denatured perfectly. Maximum activity of MDH was 19.4 unit in the s-sparganum (from snakes), 24.5 unit in the r-sparganum (from rats) and 108.0 unit in the adult worm. The maximum activity was higher in adults than in spargana. The present result showed us that the nutrients absorbed through the tegument were transferred into inner tissues and were utilized as the source of metabolism. According to the habitat of the parasite, the isozymes of LDH and MDH are activated differently, and by this different activation the sparganum and adult can adapt themselves to parasitic circumstances.

Cleavage of immunoglobulin G by excretory-secretory cathepsin S-like protease of Spirometra mansoni plerocercoid

When immunoglobulin G (IgG) was incubated with Spirometra mansoni plerocercoid (sparganum), it was cleaved into Fab and Fc fragments. Fab/c fragments were also hydrolysed. The digestion was accelerated by dithiothreitol (DTT), indicating that cleavage of IgG heavy chain was due to a cysteine protease secreted into the medium. The responsible enzyme, of M(r) 27 (+/- 0.8) kDa, was purified by a series of thiopropyl affinity, Sephacryl S-300 HR and DEAE-anion exchange chromatographies, either from worm extracts or from excretory-secretory products (ESP). The purified, thiol-dependent protease showed an optimal activity at pH 5.7 with 0.1 M sodium acetate but was active over the pH range 4.5-8.0. Its activity was inhibited completely by 10(-5) M L-trans-epoxysuccinylleucylamido(4-guanidino) butane (E-64) and 1 mM iodoacetamide (IAA), but by only 53% using the specific cathepsin L inhibitor, Z-Phe-Phe-CHN2 (5 x 10(-5) M). Partial NH2-terminal amino acid sequence was Leu-Pro-Asp-Ser-Val-Asn-Trp-Arg-Glu-Gly-Ala-Val-Thr-Ala-Val which showed 80% homology to human cathepsin S. Immunoblot analysis showed that sera from infected patients exhibited IgE antibody reaction. It is proposed that cleavage of immunoglobulin by an excreted-secreted, cathepsin S-like, allergenic protease is a mechanism of immune evasion used by the sparganum.

Purification and partial characterization of cysteine proteinase from Spirometra mansoni plerocercoids

Spirometra mansoni plerocercoids were dissected from the tissues of naturally infected snakes (Natrix trigrialateralia). Fresh plerocercoids were incubated in medium, and excretory-secretory products (E-S) were collected. In addition, soluble proteins from lyophilized plerocercoids (10 mg/ml) were extracted in 0.1 M sodium acetate. Proteinase activity was assayed with a synthetic fluorescent substrate, carbobenzoxy-phenylalanyl-arginyl-7-amino-4-trifluoromethylcoumarin. Proteinase was isolated from plerocercoid extract or E-S by diethylaminoethyl trisacryl M ion-exchange chromatography and thiolpropyl-Sepharose affinity chromatography. These separations resulted in a 12.2- (extract) and 15.6-fold (E-S) purification of proteinase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified materials revealed a 28-kDa band, consistent with the apparent native molecular weight (gel filtration chromatography) of approximately 35 kDa. Proteinases purified from whole extracts and E-S were compared for various biochemical characteristics; inhibitor profiles indicated that activities from both sources are cysteine proteinases, they exhibited identical pH curves with optima at pH 5.5 and a 50% activity range at pH 4.7-8.0, they cleaved collagen chains to 3 identical products, and they showed only minor activity toward hemoglobin. Further, the proteinase purified from plerocercoids was utilized in immunoblots with sera from sparganosis patients. Antibody (IgG) from the infected patients, but not uninfected controls, recognized the cysteine proteinase, suggesting that this antigen may be useful in the serodiagnosis of Spirometra mansoni infection.

Component proteins and protease activities in excretory-secretory product of sparganum

Spirometra mansoni plerocercoid (sparganum) was incubated in saline at 4 degrees C or 37 degrees C up to 100 hours. Protein contents in the excretory-secretory product (ESP) were rather constant (mean 7.7 mg of protein/gram of sparganum) in the preparations. Reducing SDS-PAGE of ESP showed similar protein subunit compositions with those in crude extract. Antigenic 36 and 31 kDa proteins were major bands in ESP. ESP exhibited specific activities of protease (2.9-5.3 units/mg) at pH 6.0 and pH 7.5. Presence of protease activity in ESP may be a supporting evidence that hitherto known cysteine protease of sparganum is possibly secreted.

Isolation and partial characterization of cysteine proteinase from sparganum

A proteolytic enzyme was purified from the tissue extract of spargana (plerocercoids of Spirometra erinacei) by DEAE-Trisacryl M ion exchange chromatography and thiopropyl-sepharose affinity chromatography resulted in a 21-fold purification. The proteinase activity was assayed with a synthetic fluorescent substrate, carbobenzoxy-phenylalanyl-7-amino-4-trifluoromethyl-coumarin. SDS-polyacrylamide gel electrophoresis of the purified materials revealed a single 28,000 dalton band. Inhibitor profiles of the band indicated that it belonged to cysteine endopeptidases. It exhibited identical pH curves with optimum at pH 5.5, and 50% activity from pH 4.7 to 8. It could completely degrade collagen chains to three identical products. It also showed some activity on hemoglobin. Furthermore, the band on immunoblots was reactive to the sera of sparganosis patients. These results suggest that the proteolytic enzyme belongs to cysteine proteinase which plays a role in the tissue penetration. Also it may be used as the antigen for diagnosis of active sparganosis.

The presence and possible function of methylmalonyl CoA mutase and propionyl CoA carboxylase in Spirometra mansonoides

Both spargana and adult forms of Spirometra mansonoides were shown to accumulate lactate, succinate, acetate, and propionate upon in vitro incubation. Adults differed markedly from the spargana in that quantitatively the most significant products of the former were acetate and propionate while the latter formed primarily acetate and lactate. The adults accumulated approximately 32 times more propionate than the spargana per gram of tissue. In accord with this propionate formation, propionyl CoA carboxylase and methylmalonyl CoA mutase have been found to be present in both stages of the parasite. As might be predicted, however, the activities of the carboxylase and mutase were 100-fold and 10-fold higher, respectively, in the adults as compared to the larvae. A possible physiological relationship between propionate formation and energy generation is suggested. Accordingly, inorganic 32P was incorporated into ATP upon incubation of methylmalonyl CoA with a homogenate obtained from adult S. mansonoides. Since methylmalonyl CoA mutase requires vitamin B12 coenzyme, a relationship between vitamin B12 content and propionate formation in helminths is suggested.

Metabolic fate of cyanocobalamin taken up by Spirometra mansonoides spargana

Analysis of tissue from Spirometra mansonoides spargana has shown that cyanocobalamin (vitamin B12) is metabolized to adenosylcobalamin and hydroxocobalamin. No methylcobalamin was detected. When the tissues were examined for enzymes which are known to utilize coenzyme forms of vitamin B12, only methylmalonyl CoA mutase, which requires adenosylcobalamin was found. The enzyme, tetrahydropteroylglutamate methyltransferase, which requires methylcobalamin as a cofactor, was not detected. A sizable portion of the cyanocobalamin taken up was bound to ammonium sulfate-precipitable material, suggesting that the binding substance is a protein. Vitamin B12 taken up by spargana was found to be released in vivo with a biological half-life of about 7 weeks.

Isolation and identification of a cobamide coenzyme from the tapeworm Spirometra mansonoides

A light-sensitive vitamin B12 derivative has been extracted from the adult cestode, Spirometra mansonoides. This corrinoid was identified as the cobamide coenzyme, adenosylcobalamin, by its chromatographic, chemical, and spectral properties.