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A novel type of glutathione S-transferase in Onchocerca volvulus
E Liebau1, G Wildenburg, R D Walter
1Department of Biochemistry, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.
Abstract:
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.
Insights
The parasitic worm Onchocerca volvulus releases glutathione S-transferase 1 (OvGST1), an enzyme crucial for detoxification. This secreted enzyme, OvGST1, is found in the worm
Area of Science:
- Parasitology
- Biochemistry
- Molecular Biology
Background:
- Onchocerca volvulus is a pathogenic helminth parasite.
- Helminth parasites evade host immune responses using defense mechanisms.
- Glutathione S-transferase (GST) enzymes are involved in detoxification and repair.
Purpose of the Study:
- To investigate the characteristics of a specific GST enzyme from O. volvulus.
- To determine if O. volvulus GST1 (OvGST1) is a secreted enzyme.
- To analyze the structure and potential function of OvGST1.
Main Methods:
- Sequence analysis of O. volvulus GST1 (OvGST1) cDNA.
- N-terminal sequencing of the native mature enzyme.
- Identification of potential N-glycosylation sites.
- Endoglycosidase digestion and Western blot analysis.
- Recombinant OvGST1 production in E. coli and enzymatic activity assay.
- Detection of OvGST1 in culture media and worm tissues via immunostaining.
Main Results:
- OvGST1 possesses a signal peptide characteristic of secreted proteins.
- The native OvGST1 has a unique N-terminal extension compared to other GSTs.
- OvGST1 has four potential N-glycosylation sites and at least two N-linked oligosaccharide chains.
- Recombinant, non-glycosylated OvGST1 is enzymatically active as a dimer.
- OvGST1 is secreted by adult worms in vitro and localized to the syncytial hypodermis.
Conclusions:
- OvGST1 is a secreted enzyme involved in the defense mechanisms of Onchocerca volvulus.
- The enzyme's structure and secretion suggest a role in host-parasite interactions.
- OvGST1's localization indicates potential functions in protecting the parasite from host defenses.