Peroxiredoxins (prxs) are peroxidases with broad substrate specificity. The seven prx genes expressed in Arabidopsis shoots were analyzed for their expressional response to changing photon fluence rates, oxidative stress, and ascorbate application. The results reveal a highly variable and gene-specific response to reducing and oxidizing conditions. The steady-state transcript amounts of the chloroplast-targeted prxs, namely the two-cysteine (2-Cys) prxs, prx Q and prx II E, decreased upon application of ascorbate. prx Q also responded to peroxides and diamide treatment. prx II B was induced by tertiary butylhydroperoxide, but rather unaffected by ascorbate. The strongest responses were observed for prx II C, which was induced with all treatments. The two Arabidopsis 2-Cys Prxs and four Prx II proteins were expressed heterologously in Escherichia coli. In an in vitro test system, they all showed peroxidase activity, but could be distinguished by their ability to accept dithiothreitol and thioredoxin as electron donor in the regeneration reaction. The midpoint redox potentials (E m Ј) of Prx II B, Prx II C, and Prx II E were around Ϫ290 mV and, thus, less negative than E m Ј of Prx II F, 2-Cys Prx A, and 2-Cys Prx B (Ϫ307 to Ϫ322 mV). The data characterize expression and function of the mitochondrial Prx II F and the chloroplast Prx II E for the first time, to our knowledge. Antibodies directed against 2-Cys Prx and Prx II C showed a slight up-regulation of Prx II protein in strong light and of 2-Cys Prx upon transfer both to high and low light. The results are discussed in context with the subcellular localization of the Prx gene products.Peroxiredoxins (Prxs) are enzymes that reduce hydrogen peroxide (H 2 O 2 ) and alkyl hydroperoxides. They are grouped in four classes: (a) 2-Cys Prx; (b) Prx Q; (c) Prx II, which all contain two catalytic Cys residues in distinct sequence environment; and (d) 1-Cys Prx with one conserved Cys residue only (Dietz, 2003). A phylogenetic distance analysis suggests that 2-Cys Prx, Prx Q, and 1-Cys Prx are related proteins, whereas the group of Prx II is likely to have evolved independently (Verdoucq et al., 1999;Horling et al., 2002). The catalytic Cys residues undergo oxidation during the peroxide reduction reaction and need to be reduced by electron donors such as glutaredoxins, thioredoxins, or cyclophilins before the next catalytic cycle (Lee et al., 2001;Rouhier et al., 2001;Kö nig et al., 2002). For the bacterial and animal homologs, a broad substrate specificity has been described (Nogoceke et al., 1997; Bryk et al., 2000; Hillas et al., 2000). In in vitro tests, these Prx proteins reduced H 2 O 2 , lipid peroxides, such as butyl hydroperoxide, phospholipid peroxides and cumene hydroperoxide, and peroxynitrite. For plant Prxs, the catalytic properties have only poorly been investigated.The Arabidopsis genome encodes 10 open reading frames (ORFs) for peroxiredoxins. Based on sequence similarities, they can be assigned to the four subgroups of peroxiredoxins: two ORFs code for 2...
The plant plastidial thioredoxins (Trx) are involved in the light-dependent regulation of many enzymatic activities, owing to their thiol-disulfide interchange activity. Three different types of plastidial Trx have been identified and characterized so far: the m-, f-, and x-types. Recently, a new putative plastidial type, the y-type, was found. In this work the two isoforms of Trx y encoded by the nuclear genome of Arabidopsis (Arabidopsis thaliana) were characterized. The plastidial targeting of Trx y has been established by the expression of a Trx::GFP fusion protein. Then both isoforms were produced as recombinant proteins in their putative mature forms and purified to characterize them by a biochemical approach. Their ability to activate two plastidial light-regulated enzymes, NADP-malate dehydrogenase (NADP-MDH) and fructose-1,6-bisphosphatase, was tested. Both Trx y were poor activators of fructose-1,6-bisphosphatase and NADP-MDH; however, a detailed study of the activation of NADP-MDH using site-directed mutants of its regulatory cysteines suggested that Trx y was able to reduce the less negative regulatory disulfide but not the more negative regulatory disulfide. This property probably results from the fact that Trx y has a less negative redox midpoint potential (2337 mV at pH 7.9) than thioredoxins f and m. The y-type Trxs were also the best substrate for the plastidial peroxiredoxin Q. Gene expression analysis showed that Trx y2 was mainly expressed in leaves and induced by light, whereas Trx y1 was mainly expressed in nonphotosynthetic organs, especially in seeds at a stage of major accumulation of storage lipids.Thioredoxins (Trx) are small (approximately 12 kD) ubiquitous proteins involved in thiol-disulfide exchange reactions (Buchanan, 1980;Holmgren, 1989). In higher plant cells, they are found in cytosol, mitochondria, and plastids (Schü rmann and Jacquot, 2000). All are nuclear encoded irrespective of their subcellular localization. The availability of the Arabidopsis (Arabidopsis thaliana) complete genome sequence revealed that higher plant Trxs belonged to a multigene family. Several different Trx types have been distinguished on the basis of sequence identity and intron positions, with several isoforms within each type (Meyer et al., 2002). The situation is particularly complex for plastidial Trx (cpTrx), where four different types of Trx have been found. Besides the long-time known thioredoxins m and f comprising 4 and 2 members respectively, a third type of cpTrx, named the x-type, has been recently studied and found to be a very good reductant of plastidial 2-Cys peroxiredoxins (Prxs), whereas having almost no activity with the classical target enzymes of cpTrx m and f, i.e. NADPmalate dehydrogenase (NADP-MDH) and Fru-1,6-bisphosphatase (FBPase). The fourth type has been identified quite recently (Lemaire et al., 2003) during the analysis of the genomes of Chlamydomonas reinhardtii and of the cyanobacterium Synechocystis. While only one isoform is present in the green alga and the cyanoba...
Peroxiredoxins (Prx) have recently moved into the focus of plant and animal research in the context of development, adaptation, and disease, as they function both in antioxidant defense by reducing a broad range of toxic peroxides and in redox signaling relating to the adjustment of cell redox and antioxidant metabolism. At-PrxII F is one of six type II Prx identified in the genome of Arabidopsis thaliana and the only Prx that is targeted to the plant mitochondrion. Therefore, it might be assumed to have functions similar to the human 2-Cys Prx (PRDX3) and type II Prx (PRDX5) and yeast 1-Cys Prx that likewise have mitochondrial localizations. This paper presents a characterization of PrxII F at the level of subcellular distribution, activity, and reductive regeneration by mitochondrial thioredoxin and glutaredoxin. By employing tDNA insertion mutants of A. thaliana lacking expression of AtprxII F (KO-AtPrxII F), it is shown that under optimal environmental conditions the absence of PrxII F is almost fully compensated for, possibly by increases in activity of mitochondrial ascorbate peroxidase and glutathione-dependent peroxidase. However, a stronger inhibition of root growth in KO-AtPrxII F seedlings as compared with wild type is observed under stress conditions induced by CdCl 2 as well as after administration of salicylhydroxamic acid, an inhibitor of cyanide-insensitive respiration. Simultaneously, major changes in the abundance of both nuclear and mitochondria-encoded transcripts were observed. These results assign a principal role to PrxII F in antioxidant defense and possibly redox signaling in plants cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.