Prostaglandin synthase activity of sigma- and mu-class glutathione transferases in a parasitic trematode, <i>Clonorchis sinensis</i>

Abstract

Sigma-class glutathione transferase (GST) proteins with dual GST and prostaglandin synthase (PGS) activities play a crucial role in the establishment of Clonorchis sinensis infection. Herein, we analyzed the structural and enzymatic properties of sigma-class GST (CsGST-sigma) proteins to obtain insight into their antioxidant and immunomodulatory functions in comparison with mu-class GST (CsGST-mu) proteins. CsGST-sigma proteins conserved characteristic structures, which had been described in mammalian hematopoietic prostaglandin D2 synthases. Recombinant forms of these CsGST-sigma and CsGST-mu proteins expressed in Esche & nacute;chia coli exhibited considerable degrees of GST and PGS activities with substantially different specific activities. All recombinant proteins displayed higher affinities toward prostaglandin H2 (PGS substrate; average Km of 30.7 and 3.0 mu m for prostaglandin D2 [PGDS] and E2 synthase [PGES], respectively) than those toward CDNB (GST substrate; average Km of 1,205.1 mu m). Furthermore, the catalytic efficiency (Kcat/Km) of the PGDS/PGES activity was higher than that of GST activity (average Kcat/Km of 3.1, 0.7, and 7.0 x 10-3 s-1 mu m-1 for PGDS, PGES, and GST, respectively). Our data strongly suggest that the C. sinensis sigma- and mu-class GST proteins are deeply involved in regulating host immune responses by generating PGD2 and PGE2 in addition to their roles in general detoxification.