A novel sigma-like glutathione transferase of Taenia solium metacestode

GSTs are a group of multifunctional enzymes, whose major functions involve catalysis of conjugation of glutathione thiolate anion with a multitude of bi-substrates or transportation of a range of hydrophobic ligands. Helminth GSTs are intimately involved in the scavenging of endogenously/exogenously-derived toxic compounds and xenobiotics. In this study, we identified a novel GST gene of Taenia solium metacestodes (TsMs), which is a causative agent of neurocysticercosis. The 804 bp-long cDNA encoded a 639 bp open reading frame (212 amino acid polypeptide), which exhibited the structural motif and domain organisation characteristic of GST. It formed a strong clade with trematode and insect σGSTs. We designated this cDNA as TsM σ-like GST (TsMσGST). Native TsMσGST identified through gel filtration combined with compatible immunoproteomics consisted of four isoforms at approximately 25 kDa with different pIs between 8.2 and 8.7. TsMσGST showed an enzyme activity as a homodimer and was specifically expressed in the scolex cytosol. The recombinant TsMσGST expressed in Escherichia coli showed σ-like activity with 1-chloro-2,4-dinitrobenzene (CDNB). The Vmax and Km for CDNB and glutathione (GSH) were 1.08 and 0.78 μmol/min/mg, and 0.16 and 0.17 mM, respectively. Its optimal activity was observed at pH 8.0 and at 40 °C. The enzyme activity was potently inhibited by bromosulfophthalein, and to a lesser extent by rose bengal and triphenyltin chloride. Albendazole and praziquantel non-competitively inhibited both G- and H-sites of the enzyme. To our knowledge this is the first description of the σ-class GST in cestode parasites. The enzyme might be involved in scavenging of intracellularly generated xenobiotics during homeostatic processes and anthelminthic metabolisms. Revelation of biochemical and biological properties of TsMσGST might allow us to understand pathobiological events inherent to this long-standing parasitic disease, and thus to target therapeutic intervention.

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