Abstract
Glutathione transferases (GSTs) constitute a superfamily of enzymes with essential roles in cellular detoxification and secondary metabolism in plants as in other organisms. Several plant GSTs, including those of the Phi class (GSTFs), require a conserved catalytic serine residue to perform glutathione (GSH)-conjugation reactions. Genomic analyses revealed that terrestrial plants have around ten GSTFs, eight in the Populus trichocarpa genome, but their physiological functions and substrates are mostly unknown. Transcript expression analyses showed a predominant expression of all genes both in reproductive (female flowers, fruits, floral buds) and vegetative organs (leaves, petioles). Here, we show that the recombinant poplar GSTF1 (PttGSTF1) possesses peroxidase activity toward cumene hydroperoxide and GSH-conjugation activity toward model substrates such as 2,4-dinitrochlorobenzene, benzyl and phenetyl isothiocyanate, 4-nitrophenyl butyrate and 4-hydroxy-2-nonenal but interestingly not on previously identified GSTF-class substrates. In accordance with analytical gel filtration data, crystal structure of PttGSTF1 showed a canonical dimeric organization with bound GSH or 2-(N-morpholino)ethanesulfonic acid molecules. The structure of these protein-substrate complexes allowed delineating the residues contributing to both the G and H sites that form the active site cavity. In sum, the presence of GSTF1 transcripts and proteins in most poplar organs especially those rich in secondary metabolites such as flowers and fruits, together with its GSH-conjugation activity and its documented stress-responsive expression suggest that its function is associated with the catalytic transformation of metabolites and/or peroxide removal rather than with ligandin properties as previously reported for other GSTFs.
Highlights
Glutathione transferases (GSTs; EC 2.5.1.18) represent a ubiquitous multigenic family of enzymes that conjugate the reduced tripeptide glutathione (GSH, γ-Glu-Cys-Gly) on a wide range of endogenous and exogenous electrophilic molecules (Hayes et al, 2005)
From the most recent genomic and phylogenetic analyses, the GST family is subdivided into 14 classes in photosynthetic organisms: Phi (F), Tau (U), Theta (T), Zeta (Z), Lambda (L), Hemerythrin (H), Iota (I), Ure2p, glutathionyl-hydroquinone reductase (GHR), elongation factor 1B Gamma (EF1Bγ), dehydroascorbate reductase (DHAR), tetrachlorohydroquinone dehalogenase (TCHQD), metaxin, microsomal prostaglandin E synthase type 2 (Lallement et al, 2014a)
It was shown that the GSTF1 from the black grass Alopecurus myosuroides, a weed of cereals, possesses a glutathione peroxidase activity which lowers the levels of hydroperoxides produced in response to herbicides (Cummins et al, 1999)
Summary
Glutathione transferases (GSTs; EC 2.5.1.18) represent a ubiquitous multigenic family of enzymes that conjugate the reduced tripeptide glutathione (GSH, γ-Glu-Cys-Gly) on a wide range of endogenous and exogenous electrophilic molecules (Hayes et al, 2005). Behind Tau GSTs, Phi GSTs (GSTFs) represent the second largest class in plants and this expansion probably results from several rounds of gene duplication (Lan et al, 2009) This class is often presented in the literature as plantspecific, basidiomycetes possess GSTFs (Morel et al, 2013). Arabidopsis thaliana transgenic plants expressing this GSTF1 acquire multiple herbicide resistance and accumulate protective flavonoids as initially observed in the black grass (Cummins et al, 2009, 2013). Another facet of GSTs is their involvement in secondary metabolism, in stress response and in their associated signaling. A. thaliana GSTF6 is required for the synthesis www.frontiersin.org
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
