Towards an Understanding of the Function of the Phytochelatin Synthase of Schistosoma mansoni
Open Access
- 31 January 2013
- journal article
- research article
- Published by Public Library of Science (PLoS) in PLoS Neglected Tropical Diseases
- Vol. 7 (1), e2037
- https://doi.org/10.1371/journal.pntd.0002037
Abstract
Phytochelatin synthase (PCS) is a protease-like enzyme that catalyzes the production of metal chelating peptides, the phytochelatins, from glutathione (GSH). In plants, algae, and fungi phytochelatin production is important for metal tolerance and detoxification. PCS proteins also function in xenobiotic metabolism by processing GSH S-conjugates. The aim of the present study is to elucidate the role of PCS in the parasitic worm Schistosoma mansoni. Recombinant S. mansoni PCS proteins expressed in bacteria could both synthesize phytochelatins and hydrolyze various GSH S-conjugates. We found that both the N-truncated protein and the N- and C-terminal truncated form of the enzyme (corresponding to only the catalytic domain) work through a thiol-dependant and, notably, metal-independent mechanism for both transpeptidase (phytochelatin synthesis) and peptidase (hydrolysis of GSH S-conjugates) activities. PCS transcript abundance was increased by metals and xenobiotics in cultured adult worms. In addition, these treatments were found to increase transcript abundance of other enzymes involved in GSH metabolism. Highest levels of PCS transcripts were identified in the esophageal gland of adult worms. Taken together, these results suggest that S. mansoni PCS participates in both metal homoeostasis and xenobiotic metabolism rather than metal detoxification as previously suggested and that the enzyme may be part of a global stress response in the worm. Because humans do not have PCS, this enzyme is of particular interest as a drug target for schistosomiasis. Schistosomiasis is a chronic, debilitating disease that affects hundreds of millions of people. The treatment of schistosomiasis relies solely on monotherapy with praziquantel and there is concern that drug-resistant parasites will evolve. Therefore, it is imperative to identify new drugs for schistosomiasis treatment. In this study our goal was to characterize the function of the phytochelatin synthase of Schistosoma mansoni, previously suggested as a candidate for drug targeting to control schistosomiasis. Phytochelatin synthase catalyzes the production of metal chelating peptides, the phytochelatins, from glutathione (GSH). In plants, algae, and fungi phytochelatin production is important for metal tolerance and detoxification. PCS proteins also function in the elimination of xenobiotics by processing GSH S-conjugates. We found that SmPCS expressed in bacteria could both synthesize phytochelatins and hydrolyze various GSH S-conjugates. We found the enzyme works through a thiol-dependant and, notably, metal-independent mechanism for both transpeptidase (phytochelatin synthesis) and peptidase (hydrolysis of GSH S-conjugates) activities. The expression of the PCS gene in adult schistosome worms was increased by exposure to a number of metals and xenobiotics. In addition, these treatments were found to increase the expression of other enzymes involved in GSH metabolism. Highest levels of PCS transcripts were localized in the esophageal gland of adult worms. Taken together, these results suggest that S. mansoni PCS participates in both metal homoeostasis and xenobiotic metabolism rather than metal detoxification as previously suggested and that it may be part of a global stress response in the worm.Keywords
This publication has 57 references indexed in Scilit:
- A Research Agenda for Helminth Diseases of Humans: Basic Research and Enabling Technologies to Support Control and Elimination of HelminthiasesPLoS Neglected Tropical Diseases, 2012
- Whole mount in situ hybridization methodology for Schistosoma mansoniMolecular and Biochemical Parasitology, 2011
- Characterization of the Phytochelatin Synthase of Schistosoma mansoniPLoS Neglected Tropical Diseases, 2011
- Linking toxicant physiological mode of action with induced gene expression changes in Caenorhabditis elegansBMC Systems Biology, 2010
- Detoxification of Multiple Heavy Metals by a Half-Molecule ABC Transporter, HMT-1, and Coelomocytes of Caenorhabditis elegansPLOS ONE, 2010
- Towards an understanding of the mechanism of action of praziquantelMolecular and Biochemical Parasitology, 2008
- Free radicals and antioxidants in normal physiological functions and human diseaseThe International Journal of Biochemistry & Cell Biology, 2007
- Toxicogenomic analysis of Caenorhabditis elegans reveals novel genes and pathways involved in the resistance to cadmium toxicityGenome Biology, 2007
- Mutagenic Definition of a Papain-Like Catalytic Triad, Sufficiency of the N-Terminal Domain for Single-Site Core Catalytic Enzyme Acylation, and C-Terminal Domain for Augmentative Metal Activation of a Eukaryotic Phytochelatin SynthasePlant Physiology, 2006
- A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye bindingAnalytical Biochemistry, 1976