Engineering functional artificial hybrid proteins between poplar peroxiredoxin II and glutaredoxin or thioredoxin

Oxidative stress management in the filamentous, heterocystous, diazotrophic cyanobacterium, Anabaena PCC7120

Reactive oxygen species (ROS) are inevitably generated as by-products of respiratory/photosynthetic electron transport in oxygenic photoautotrophs. Unless effectively scavenged, these ROS can damage all cellular components. The filamentous, heterocystous, nitrogen-fixing strains of the cyanobacterium, Anabaena, serve as naturally abundant contributors of nitrogen biofertilizers in tropical rice paddy fields. Anabaena strains are known to tolerate several abiotic stresses, such as heat, UV, gamma radiation, desiccation, etc., that are known to generate ROS. ROS are detoxified by specific antioxidant enzymes like superoxide dismutases (SOD), catalases and peroxiredoxins. The genome of Anabaena PCC7120 encodes two SODs, two catalases and seven peroxiredoxins, indicating the presence of an elaborate antioxidant enzymatic machinery to defend its cellular components from ROS. This article summarizes recent findings and depicts important perspectives in oxidative stress management in Anabaena PCC7120.

A novel glutaredoxin domain-containing peroxiredoxin ‘All1541’ protects the N2-fixing cyanobacterium Anabaena PCC 7120 from oxidative stress

Prxs (peroxiredoxins) are ubiquitous thiol-based peroxidases that detoxify toxic peroxides. The Anabaena PCC 7120 genome harbours seven genes/ORFs (open reading frames) which have homology with Prxs. One of these (all1541) was identified to encode a novel Grx (glutaredoxin) domain-containing Prx by bioinformatic analysis. A recombinant N-terminal histidine-tagged All1541 protein was overexpressed in Escherichia coli and purified. Analysis with the protein alkylating agent AMS (4-acetamido-4′-maleimidyl-stilbene-2,2′-disulfonate) showed All1541 to form an intra-molecular disulfide bond. The All1541 protein used glutathione (GSH) more efficiently than Trx (thioredoxin) to detoxify H2O2. Deletion of the Grx domain from All1541 resulted in loss of GSH-dependent peroxidase activity. Employing site-directed mutagenesis, the cysteine residues at positions 50 and 75 were identified as peroxidatic and resolving cysteine residues respectively, whereas both the cysteine residues within the Grx domain (positions 181 and 184) were shown to be essential for GSH-dependent peroxidase activity. On the basis of these data, a reaction mechanism has been proposed for All1541. In vitro All1541 protein protected plasmid DNA from oxidative damage. In Anabaena PCC 7120, all1541 was transcriptionally activated under oxidative stress. Recombinant Anabaena PCC 7120 strain overexpressing All1541 protein showed superior oxidative stress tolerance to H2O2 as compared with the wild-type strain. The results suggest that the glutathione-dependent peroxidase All1541 plays an important role in protecting Anabaena from oxidative stress.

Multiple catalytically active thioredoxin folds: a winning strategy for many functions

The Thioredoxin (Trx) fold is a versatile protein scaffold consisting of a four-stranded β-sheet surrounded by three α-helices. Various insertions are possible on this structural theme originating different proteins, which show a variety of functions and specificities. During evolution, the assembly of different Trx fold domains has been used many times to build new multi-domain proteins able to perform a large number of catalytic functions. To clarify the interaction mode of the different Trx domains within a multi-domain structure and how their combination can affect catalytic performances, in this review, we report on a structural and functional analysis of the most representative proteins containing more than one catalytically active Trx domain: the eukaryotic protein disulfide isomerases (PDIs), the thermophilic protein disulfide oxidoreductases (PDOs) and the hybrid peroxiredoxins (Prxs).

The peroxiredoxin and glutathione peroxidase families in Chlamydomonas reinhardtii

Thiol/selenol peroxidases are ubiquitous nonheme peroxidases. They are divided into two major subfamilies: peroxiredoxins (PRXs) and glutathione peroxidases (GPXs). PRXs are present in diverse subcellular compartments and divided into four types: 2-cys PRX, 1-cys PRX, PRX-Q, and type II PRX (PRXII). In mammals, most GPXs are selenoenzymes containing a highly reactive selenocysteine in their active site while yeast and land plants are devoid of selenoproteins but contain nonselenium GPXs. The presence of a chloroplastic 2-cys PRX, a nonselenium GPX, and two selenium-dependent GPXs has been reported in the unicellular green alga Chlamydomonas reinhardtii. The availability of the Chlamydomonas genome sequence offers the opportunity to complete our knowledge on thiol/selenol peroxidases in this organism. In this article, Chlamydomonas PRX and GPX families are presented and compared to their counterparts in Arabidopsis, human, yeast, and Synechocystis sp. A summary of the current knowledge on each family of peroxidases, especially in photosynthetic organisms, phylogenetic analyses, and investigations of the putative subcellular localization of each protein and its relative expression level, on the basis of EST data, are presented. We show that Chlamydomonas PRX and GPX families share some similarities with other photosynthetic organisms but also with human cells. The data are discussed in view of recent results suggesting that these enzymes are important scavengers of reactive oxygen species (ROS) and reactive nitrogen species (RNS) but also play a role in ROS signaling.

Functional analysis and expression characteristics of chloroplastic Prx IIE

Peroxiredoxins (Prxs) are ubiquitous thiol-dependent peroxidases capable of eliminating a variety of peroxides through reactive catalytic cysteines, which are regenerated by reducing systems. Based on amino acid sequences and their mode of catalysis, five groups of thiol peroxidases have been distinguished in plants, and type II Prx is one of them with representatives in many sub-cellular compartments. The mature form of poplar chloroplastic Prx IIE was expressed as a recombinant protein in Escherichia coli. The protein is able to reduce H2O2 and tert-butyl hydroperoxide and is regenerated by both glutaredoxin (Grx) and thioredoxin (Trx) systems. Nevertheless, compared with Trxs, Grxs, and more especially chloroplastic Grx S12, are far more efficient reductants towards Prx IIE. The expression of Prx IIE at both the mRNA and protein levels as a function of organ type and abiotic stress conditions was investigated. Western blot analysis revealed that Prx IIE gene is constitutively expressed in Arabidopsis thaliana, mostly in young and mature leaves and in flowers. Under photo-oxidative treatment and water deficit, almost no change was observed in the abundance of Prx IIE in A. thaliana, while the level of Prx Q (one of the two other chloroplastic Prxs with 2-Cys Prx) increased in response to both stresses, indicating that plastidic members of the Prx family exhibit specific patterns of expression under stress.

The Two-Domain Structure of 5‘-Adenylylsulfate (APS) Reductase from Enteromorpha intestinalis Is a Requirement for Efficient APS Reductase Activity

5'-Adenylylsulfate (APS) reductase from Enteromorpha intestinalis (EiAPR) is composed of two domains that function together to reduce APS to sulfite. The carboxyl-terminal domain functions as a glutaredoxin that mediates the transfer of electrons from glutathione to the APS reduction site on the amino-terminal domain. To study the basis for the interdomain interaction, a heterologous system was constructed in which the C domain of EiAPR was fused to the carboxyl terminus of the APS reductase from Pseudomonas aeruginosa (PaAPR), an enzyme that normally uses thioredoxin as an electron donor and is incapable of using glutathione for this function. The hybrid enzyme, which retains the [4Fe-4S] cluster from PaAPR, was found to use both thioredoxin and glutathione as an electron donor for APS reduction. The ability to use glutathione was enhanced by the addition of Na2SO4 to the reaction buffer, a property that the hybrid enzyme shares with EiAPR. When the C domain was added as a separate component, it was much less efficient in conferring PaAPR with the ability to use glutathione as an electron donor, despite the fact that the separately expressed C domain functioned in two activities that are typical for glutaredoxins, hydroxyethyl disulfide reduction and electron donation to ribonucleotide reductase. These results suggest that the physical connection of the reductase and C domain on a single polypeptide is critical for the electron-transfer reaction. Moreover, the effect of Na2SO4 suggests that a water-ordering component of the reaction milieu is critical for the catalytic function of plant-type APS reductases by promoting the interdomain interaction.

Protein-protein interactions within peroxiredoxin systems

Peroxiredoxin systems in plants were demonstrated involved in crucial roles related to reactive oxygenated species (ROS) metabolism and the linked cell signalling to ROS. Peroxiredoxins function as peroxidasic systems that combine at least a reactivating reductant agent like thioredoxins, and sometimes glutaredoxins and glutathion. In the past three years a number of peroxiredoxin structures were solved by crystallography in different experimental crystallisation conditions. The structures have revealed a significant propensity of peroxiredoxins for oligomerism that was confirmed by biophysical studies in solution using NMR and other methods as analytical ultra-centrifugation. These studies showed that quaternary structures of peroxiredoxins involve specific protein-protein interaction interfaces that rely upon the peroxiredoxin types and/or their redox conditions. The protein-protein interactions with the reactivating redoxins essentially lead to transient unstable complexes. We review herein the different protein-protein interactions characterized or deduced from those reports.

Glutathionylation induces the dissociation of 1-Cys D-peroxiredoxin non-covalent homodimer

1-Cys peroxiredoxins (1-Cys Prxs) are antioxidant enzymes that catalyze the reduction of hydroperoxides into alcohols using a strictly conserved cysteine. 1-Cys B-Prxs, homologous to human PrxVI, were recently shown to be reactivated by glutathione S-transferase (GST) pi via the formation of a GST-Prx heterodimer and Prx glutathionylation. In contrast, 1-Cys D-Prxs, homologous to human PrxV, are reactivated by the glutaredoxin-glutathione system through an unknown mechanism. To investigate the mechanistic events that mediate the 1-Cys D-Prx regeneration, interaction of the Prx with glutathione was studied by mass spectrometry and NMR. This work reveals that the Prx can be glutathionylated on its active site cysteine. Evidences are reported that the glutathionylation of 1-Cys D-Prx induces the dissociation of the Prx non-covalent homodimer, which can be recovered by reduction with dithiothreitol. This work demonstrates for the first time the existence of a redox-dependent dimer-monomer switch in the Prx family, similar to the decamer-dimer switch for the 2-Cys Prxs.