Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: HUMANGGP:005732 (peroxiredoxin 6)
 336 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A new type of peroxidase enzyme, named thioredoxin peroxidase (TPx), that reduces H2O2 with the use of electrons from thioredoxin and contains two essential cysteines was recently identified. TPx homologs, termed peroxiredoxin (Prx), have also been identified and include several proteins, designated 1-Cys Prx, that contain only one conserved cysteine. Recombinant human 1-Cys Prx expressed in and purified from Escherichia coli has now been shown to reduce H2O2 with electrons provided by dithiothreitol. Furthermore, human 1-Cys Prx transiently expressed in NIH 3T3 cells was able to remove intracellular H2O2 generated in response either to the addition of exogenous H2O2 or to treatment with platelet-derived growth factor. The conserved Cys47-SH group was shown to be the site of oxidation by H2O2. Thus, mutation of Cys47 to serine abolished peroxidase activity. Moreover, the oxidized intermediate appears to be Cys-SOH. In contrast to TPx, in which one of the two conserved cysteines is oxidized to Cys-SOH and then immediately reacts with the second conserved cysteine of the second subunit of the enzyme homodimer to form an intermolecular disulfide, the Cys-SOH of 1-Cys Prx does not form a disulfide. Neither thioredoxin, which reduces the disulfide of TPx, nor glutathione, which reduces the Cys-SeOH of oxidized glutathione peroxidase, was able to reduce the Cys-SOH of 1-Cys Prx and consequently could not support peroxidase activity. Human 1-Cys Prx was previously shown to exhibit a low level of phospholipase A2 activity at an acidic pH; the enzyme was thus proposed to be lysosomal, and Ser32 was proposed to be critical for lipase function. However, the mutation of Ser32 or Cys47 has now been shown to have no effect on the lipase activity of 1-Cys Prx, which was also shown to be a cytosolic protein. Thus, the primary cellular function of 1-Cys Prx appears to be to reduce peroxides with the use of electrons provided by an as yet unidentified source; the enzyme therefore represents a new type of peroxidase.
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PMID:Characterization of a mammalian peroxiredoxin that contains one conserved cysteine. 949 58

Prior studies have shown that filarial nematodes can effectively metabolize hydrogen peroxide in excess of that generated by activated host cells. However, the mechanisms of H2O2 removal by the filarial parasites are unclear. Herein we report the results of studies carried out on the biochemical activity and on immunolocalization of a recombinant peroxiredoxin (Prx) enzyme from the dog filarial parasite Dirofilaria immitis. A full-length cDNA encoding a 1-Cys Prx enzyme from the dog heartworm D. immitis was expressed in Escherichia coli as a recombinant polyhistidine fusion protein (rDiPrx-1). rDiPrx-1 was capable of reducing H2O2 in the presence of dithiothreitol. The apparent kinetic constants determined for DiPrx-1 using H2O2 as a substrate were a Michaelis constant (Km) of 16.28 mM and a maximal velocity (Vmax) of 16 micromol/min(-1). Consistent with the enzyme activity, D. immitis adult worms could detoxify exogenously added H2O2 in vitro. Antibodies to rDiPrx-1 identified a 27-kDa native antigen in parasite extracts and larval and adult excretory-secretory products. The antibodies were used to localize the native antigen to the lateral hypodermal chords of both male and female worms by immunohistochemistry. In addition, labeling was seen in the afibrillar muscle cells in male worms and in some areas of the uterine wall in female worms. Thus, DiPrx-1 is the first parasite Prx to be shown to detoxify exogenously added H2O2 in an in vitro system.
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PMID:Removal of hydrogen peroxide by a 1-cysteine peroxiredoxin enzyme of the filarial parasite Dirofilaria immitis. 1072 90

Peroxiredoxins (Trx-Px) are ubiquitous antioxidant enzymes that catalyse the thioredoxin-dependent reduction of hydroperoxides. The number of characteristic active site (VCP/T) motifs defines these proteins as 1-Cys and 2-Cys Trx-Px. Steady-state kinetic parameters of Plasmodium falciparum 2-Cys Trx-Px (PfTrx-Px1) were determined using stopped flow rapid kinetics. The bi-substrate reaction displays ping-pong kinetics and the K(m) values for H2O2 and thioredoxin were determined to be 0.78+/-0.14 microM and 18.94+/-3.01 microM, respectively. The Vmax(app) and kcat(app) for H2O2 were found to be 4+/-0.6 U mg(-1) and 1.67+/-0.25 s(-1), respectively and those for thioredoxin are 23.0+/-0.2 U mg(-1) and 9.65+/-0.1 s(-1), emphasising the specificity of the enzyme for the substrate H2O2. After subjection to exogenous and endogenous oxidative stress, P. falciparum blood stage forms showed a marked elevation of PfTrx-Px1 mRNA and protein levels consistent with the hypothesis that it is an important component of the parasite's antioxidant machinery. Gel filtration, cross-linking and electron microscopy (EM) revealed that the protein forms decamers consisting of pentamers of homodimers that have a doughnut-like shape consistent with the structures of related proteins. No dimeric forms of the protein were detectable after gel filtration suggesting that PfTrx-Px1 predominantly exists as an oligomer.
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PMID:2-Cys peroxiredoxin PfTrx-Px1 is involved in the antioxidant defence of Plasmodium falciparum. 1294 43

Peroxiredoxin VI (PrxVI) is a bifunctional enzyme with non-selenium glutathione peroxidase and Ca2+-independent acidic phospholipase A2 activities. We demonstrate that transfection-mediated PrxVI overexpression protects immortalized human WI-38 and murine NIH3T3 fibroblasts against cytotoxic doses of tert-butylhydroperoxide and H2O2. Mutants for either glutathione peroxidase or phospholipase A2 activity show that glutathione peroxidase but not phospholipase A2 activity is required to promote cell survival after stress. Also, ectopic PrxVI overexpression does not protect telomerase-stabilized WI-38 fibroblasts against stress-induced premature senescence.
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PMID:Role of the PLA2-independent peroxiredoxin VI activity in the survival of immortalized fibroblasts exposed to cytotoxic oxidative stress. 1474 36

Peroxiredoxin 6 (Prdx6), a bifunctional 25-kDa protein with both GSH peroxidase and phospholipase A2 activities, is the only mammalian 1-Cys member of the peroxiredoxin superfamily and is expressed in all major organs, with a particularly high level in lung. Prdx6 uses GSH as an electron donor to reduce H2O2 and other hydroperoxides including phospholipid hydroperoxides at approximately 5 micromol/mg protein/min with K1 approximately 3 x 10(6) M(-1) s(-1). Oxidation of the Cys47 to a sulfenic acid during catalysis requires piGST-catalyzed glutathionylation and reduction with GSH to complete the enzymatic cycle. Prdx6 stably overexpressed in cells protected against oxidative stress, whereas antisense treatment resulted in oxidant stress and apoptosis. Adenoviral-mediated overexpression of Prdx6 in mouse lungs protected against the toxicity of hyperoxia, whereas Prdx6-null mice were more sensitive to the effects of hyperoxia or paraquat. We postulate that Prdx6 functions in antioxidant defense mainly by facilitating repair of damaged cell membranes via reduction of peroxidized phospholipids. The PLA2 activity of Prdx6 is Ca2+ independent and maximal at acidic pH. Inhibition of PLA2 activity results in alterations of lung surfactant phospholipid synthesis and turnover. Thus, Prdx6, a unique mammalian peroxiredoxin, is an important antioxidant enzyme and has a major role in lung phospholipid metabolism.
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PMID:Peroxiredoxin 6, a 1-Cys peroxiredoxin, functions in antioxidant defense and lung phospholipid metabolism. 1589 Jun 16

Peroxiredoxins (Prxs) are thiol-dependent peroxidases that catalyze the detoxification of various peroxide substrates such as H2O2, peroxinitrite, and hydroperoxides, and control some signal transduction in eukaryotic cells. Prxs are found in all cellular organisms and represent an enormous superfamily. Recent genome sequencing projects and biochemical studies have identified a novel subfamily, the archaeal Prxs. Their primary sequences are similar to those of the 1-Cys Prxs, which use only one cysteine residue in catalysis, while their catalytic properties resemble those of the typical 2-Cys Prxs, which utilize two cysteine residues from adjacent monomers within a dimer in catalysis. We present here the X-ray crystal structure of an archaeal Prx from the aerobic hyperthermophilic crenarchaeon, Aeropyrum pernix K1, determined at 2.3 A resolution (Rwork of 17.8% and Rfree of 23.0%). The overall subunit arrangement of the A.pernix archaeal Prx is a toroid-shaped pentamer of homodimers, or an (alpha2)5 decamer, as observed in the previously reported crystal structures of decameric Prxs. The basic folding topology and the peroxidatic active site structure are essentially the same as those of the 1-Cys Prx, hORF6, except that the C-terminal extension of the A.pernix archaeal Prx forms a unique helix with its flanking loops. The thiol group of the peroxidatic cysteine C50 is overoxidized to sulfonic acid. Notably, the resolving cysteine C213 forms the intra-monomer disulfide bond with the third cysteine, C207, which should be a unique structural characteristic in the many archaeal Prxs that retain two conserved cysteine residues in the C-terminal region. The conformational flexibility near the intra-monomer disulfide linkage might be necessary for the dramatic structural rearrangements that occur in the catalytic cycle.
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PMID:Crystal structure of an archaeal peroxiredoxin from the aerobic hyperthermophilic crenarchaeon Aeropyrum pernix K1. 1621 69

Glutathione S-transferase pi (GST pi) has been shown to reactivate oxidized 1-cysteine peroxiredoxin (1-Cys Prx, Prx VI, Prdx6, and AOP2). We now demonstrate that a heterodimer complex is formed between 1-Cys Prx with a C-terminal His6 tag and GST pi upon incubation of the two proteins at pH 8.0 in buffer containing 20% 1,6-hexanediol to dissociate the homodimers, followed by dialysis against buffer containing 2.5 mM glutathione (GSH) but lacking 1,6-hexanediol. The heterodimer can be purified by chromatography on nickel-nitriloacetic acid agarose in the presence of GSH. N-Terminal sequencing showed that equimolar amounts of the two proteins are present in the isolated complex. In the heterodimer, 1-Cys Prx is fully active toward either H2O2 or phospholipid hydroperoxide, while the GST pi activity is approximately 25% of that of the GST pi homodimer. In contrast, the 1-Cys Prx homodimer lacks peroxidase activity even in the presence of free GSH. The heterodimer is also formed in the presence of S-methylglutathione, but no 1-Cys Prx activity is found under these conditions. The yield of heterodimer is decreased in the absence of 1,6-hexanediol or GSH. Rapid glutathionylation of 1-Cys Prx in the heterodimer is detected by immunoblotting. Subsequently, a disulfide-linked dimer is observed on SDS-PAGE, and the free cysteine content is decreased by 2 per heterodimer. The involvement of particular binding sites in heterodimer formation was tested by site-directed mutagenesis of the two proteins. For 1-Cys Prx, neither Cys47 nor Ser32 is required for heterodimer formation but Cys47 is essential for 1-Cys Prx activation. For GST pi, Cys47 and Tyr7 (at or near the GSH-binding site) are needed for heterodimer formation but three other cysteines are not. We conclude that reactivation of oxidized 1-Cys Prx by GST pi occurs by heterodimerization of 1-Cys Prx and GST pi harboring bound GSH, followed by glutathionylation of 1-Cys Prx and then formation of an intersubunit disulfide. Finally, the GSH-mediated reduction of the disulfide regenerates the reduced active-site sulfhydryl of 1-Cys Prx.
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PMID:Direct evidence for the formation of a complex between 1-cysteine peroxiredoxin and glutathione S-transferase pi with activity changes in both enzymes. 1640 Oct 67

Bcp2 was identified as a putative peroxiredoxin (Prx) in the genome database of the aerobic hyperthermophilic archaeon Sulfolobus solfataricus. Its role in oxidative stress was investigated by transcriptional analysis of RNA isolated from cultures that had been stressed with various oxidant agents. Its specific involvement was confirmed by a considerable increase in the bcp2 transcript following induction with H2O2. The 5' end of the transcript was mapped by primer extension analysis and the promoter region was characterized. bcp2 was cloned and expressed in Escherichia coli, the recombinant enzyme was purified and the predicted molecular mass was confirmed. Using dithiothreitol as an electron donor, this enzyme acts as a catalyst in H2O2 reduction and protects plasmid DNA from nicking by the metal-catalysed oxidation system. Western blot analysis revealed that the Bpc2 expression was induced as a cellular adaptation in response to the addition of exogenous stressors. The results obtained indicate that Bcp2 plays an important role in the peroxide-scavaging system in S. solfataricus. Mutagenesis studies have shown that the only cysteine, Cys49, present in the Bcp2 sequence, is involved in the catalysis. Lastly, the presence of this Cys in the sequence confirms that Bcp2 is the first archaeal 1-Cysteine peroxiredoxin (1-Cys Prx) so far identified.
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PMID:Identification and characterization of 1-Cys peroxiredoxin from Sulfolobus solfataricus and its involvement in the response to oxidative stress. 1644 59

Methodologies and results of studies on the kinetics of peroxiredoxins (Prx) are reviewed. Peroxiredoxins are broad-spectrum peroxidases that catalyze the reduction of H2O2, organic hydroperoxides and peroxynitrite by thiols. Their catalytic cycle starts with the oxidation of a particularly reactive cysteine residue (C(P)) to a sulfenic acid derivative by the peroxide substrate, the sulfenic acid then reacts with a thiol to form a disulfide, and the cycle is completed by thiol/disulfide exchange reactions that regenerate the ground-state enzyme. Depending on the subtype of peroxiredoxin, the thiol reacting with the primary oxidation product (E-SOH) may be a cysteine residue of a second subunit (typical 2-Cys Prx), a cysteine residue of the same subunit (atypical 2-Cys Prx) or reducing substrate (1-Cys Prx and at least one example of an atypical 2-Cys Prx). In a typical 2-Cys Prx the intra-subunit disulfide formation with the second "resolving" cysteine (C(R)) is mandatory for the reduction by the specific substrate, which is a protein characterized by a CXXC motif such as thioredoxin, tryparedoxin or AhpF. These consecutive redox reactions define the catalysis as an enzyme substitution mechanism, which is corroborated by a ping-pong pattern that is commonly observed in steady-state analyses, chemical identification of catalytic intermediates and stopped-flow analyses of partial reactions. More complex kinetic patterns are discussed in terms of cooperativity between the subunits of the oligomeric enzymes, generation of different oxidized intermediates or partial over-oxidation of C(P) to a sulfinic acid. Saturation kinetics is often not observed indicating that a typical complex between reduced enzyme and hydroperoxide is not formed and that, in these cases, formation of the complex between the oxidized enzyme and its reducing substrate is slower than the reaction within this complex. Working with sulphur catalysis, Prxs are usually less efficient than the heme- or selenium-containing peroxidases, but in some cases the k(+1) values (bimolecular rate constant for oxidation of reduced E by ROOH) are comparable, the overall range being 2 x 10(3)-4 x 10(7) M(-1)s(-1) depending on the hydroperoxide and the individual Prx. For the reduction of peroxynitrite k(+1) values of 1 x 10(6) up to 7 x 10(7) M(-1)s(-1) have been measured. The net forward rate constants k'(+2) for the reductive part of the cycle range between 2 x 10(4)-1 x 10(7) M(-1)s(-1). These kinetic characteristics qualify the peroxiredoxins as moderately efficient devices to detoxify hydroperoxides, which is pivotal to organisms devoid of more efficient peroxidases, and as most relevant to the detoxification of peroxynitrite. In higher organisms, their specific role is seen in the regulation of signalling cascades that are modulated by H2O2, lipid hydroperoxides or peroxynitrite.
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PMID:Kinetics of peroxiredoxins and their role in the decomposition of peroxynitrite. 1808 91

Peroxiredoxins (Prxs) play an important role against various oxidative stresses and intra-cellular signal transduction. Peroxiredoxin 6 (PrxVI) was identified from the disk abalone Haliotis discus discus cDNA library and named HdPrxVI. The full length cDNA of HdPrxVI was 1457 bp with a 654 bp open reading frame (ORF) encoding 218 amino acids. The predicted molecular mass and estimated isoelectric point (pI) of HdPrxVI were 24 kDa and 7.3, respectively. The deduced amino acid sequence demonstrated the greatest degree (72.4%) of identity with Crassostrea gigas PrxVI. The conserved peroxidase catalytic center (42PVCTTE47) with a conserved cysteine residue (Cys44) and a catalytic center for PLA2 activity (27GGSWA31) were observed in the sequence, indicating that it is a member of 1-Cys Prx. Real time PCR results revealed that HdPrxVI mRNA is constitutively expressed in all tissues in a tissue-specific manner. During exposure to haemorrhagic septicaemia virus (VHSV), HdPrxVI mRNA transcription was down-regulated in the gill, suggesting that the abalone responded to the viral infection quickly, and HdPrxVI played a physiological role against virus-induced oxidative stress. The purified recombinant HdPrxVI, together with dithiothreitol (DTT), was shown to scavenge H2O2 in human leukemia THP-1 cells and provided protection against H2O2-induced apoptosis.
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PMID:Molecular cloning, characterization and expression analysis of peroxiredoxin 6 from disk abalone Haliotis discus discus and the antioxidant activity of its recombinant protein. 1946 Apr 42


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