Plant Glutathione Peroxidases Are Functional Peroxiredoxins Distributed in Several Subcellular Compartments and Regulated during Biotic and Abiotic Stresses

Abstract

We provide here an exhaustive overview of the glutathione (GSH) peroxidase (Gpx) family of poplar (Populus trichocarpa). Although these proteins were initially defined as GSH dependent, in fact they use only reduced thioredoxin (Trx) for their regeneration and do not react with GSH or glutaredoxin, constituting a fifth class of peroxiredoxins. The two chloroplastic Gpxs display a marked selectivity toward their electron donors, being exclusively specific for Trxs of the y type for their reduction. In contrast, poplar Gpxs are much less specific with regard to their electron-accepting substrates, reducing hydrogen peroxide and more complex hydroperoxides equally well. Site-directed mutagenesis indicates that the catalytic mechanism and the Trx-mediated recycling process involve only two (cysteine [Cys]-107 and Cys-155) of the three conserved Cys, which form a disulfide bridge with an oxidation-redox midpoint potential of 2295 mV. The reduction/formation of this disulfide is detected both by a shift on sodium dodecyl sulfate-polyacrylamide gel electrophoresis or by measuring the intrinsic tryptophan fluorescence of the protein. The six genes identified coding for Gpxs are expressed in various poplar organs, and two of them are localized in the chloroplast, with one colocalizing in mitochondria, suggesting a broad distribution of Gpxs in plant cells. The abundance of some Gpxs is modified in plants subjected to environmental constraints, generally increasing during fungal infection, water deficit, and metal stress, and decreasing during photooxidative stress, showing that Gpx proteins are involved in the response to both biotic and abiotic stress conditions.

Structural Basis for a Distinct Catalytic Mechanism in Trypanosoma brucei Tryparedoxin Peroxidase

“…Whereas the spectra of poplar TxP reflect a switch from a hydrophobic environment in the reduced state to an exposed conformation in the oxidized state (43), the tryptophan fluorescence emission spectra of oxidized and reduced Px III are identical and in accordance with an exposed position of Trp 137 in both forms (supplemental Fig. S4).…”

“…This loop is not present in the monomeric human GPX4 (PDB code 2GS3 and 2OBI (42)) as well as in most of the cysteine-containing glutathione peroxidase-type proteins including poplar TxP (16). Nevertheless, the latter forms a homodimer (42,43). This protein dimerizes through the C-terminal region (16).…”

Inactivation of Thioredoxin Reductases Reveals a Complex Interplay between Thioredoxin and Glutathione Pathways in Arabidopsis Development

“…This function was clearly demonstrated by genetic means for some chloroplast thioredoxins (Vieira Dos Santos and Rey, 2006). An antioxidant function of the NTS is suggested even in the cytosol and mitochondria by the presence of the misnamed plant glutathione peroxidases (GPXs), which are in fact thioredoxin-dependent peroxidases (Iqbal et al, 2006;Navrot et al, 2006), and of peroxiredoxins (PRXs), some reducible by thioredoxins (Brehelin et al, 2003) and others by glutaredoxins (Dietz, 2003). The simplest interpretation is that the alternative thioredoxin reduction pathway is sufficient to allow optimal function of the GPXs and PRXs in the ntra ntrb mutant.…”

Structural and functional characterization of tree proteins involved in redox regulation: a new frontier in forest science

“…Including glutathione peroxidases, there are five classes of thioredoxin peroxidases in plants based on their amino acid sequence and oligomerization state . Several of them are solely dependent on thioredoxin for their regeneration (Rouhier et al 2004b;Navrot et al 2006), but surprisingly our initial data which concerned a specific class called atypical type II peroxiredoxin (later referred to as poplar PrxIIB) indicated that they could be regenerated equally well by thioredoxin and glutaredoxin (Rouhier et al 2001(Rouhier et al , 2002a. That glutaredoxins could be an alternate reducing system to atypical type II peroxiredoxins was unknown at that time in other biological organisms.…”