Characterization of catalytic and non-catalytic activities of EgGST2-3, a heterodimeric glutathione transferase from Echinococcus granulosus.

Glutathione transferases (GSTs) perform several catalytic and non-catalytic roles in the defense against toxicities of electrophile compounds and oxidative stress, and therefore are involved in stress-response and cell detoxification. Previously, we have provided evidence indicating that EgGST2 and EgGST3, two phylogenetically distant Echinococcus granulosus GSTs, can naturally form a heterodimeric structure (EgGST2-3). In the present work, the recombinant heterodimer GST (rEgGST2-3) is characterized. Hence, rEgGST2-3 was able to conjugate GSH to three substrates: 1-chloro-2,4-dinitrobenzene (CDNB, general substrate for GSTs), 1,2-dichloro-4-nitrobenzene (specific substrate for mammalian Mu class) and trans,trans-deca-2,4-dienal (reactive carbonyl). The canonical activity was considerably reduced by all the conventional inhibitors (cybacron blue, triphenylthin chloride and bromosulfophthalein) and by other inhibitors (ellagic acid, alizarin and chenodeoxycholic acid). Besides this, rEgGST2-3 activity was inhibited by a number of anthelmintic drugs, where the halogenated phenolic drugs (mainly bithionol and hexachlorophene) acted as stronger inhibitors, suggesting they may bind to the EgGST2-3. Moreover, rEgGST2-3 exhibited glutathione-peroxidase activity, and its specific constant (k/K) was calculated. Finally, rEgGST2-3 displayed the ability to bind non-substrate molecules, particularly anthelmintic drugs, suggesting that ligandin activity may have potential to act as a passive protection parasite mechanism. Overall, the rEgGST2-3 behavior was shown to be both complementary and redundant to that reported for rEgGST1, another characterized GST from E. granulosus. It would be appropriate that different enzymes in the same organism do not have exactly the same functional properties to develop a better adaptation to life in the host.