A novel anti-peroxiredoxin autoantibody in patients with Kawasaki disease

Antibodies to the anti-oxidative peroxiredoxin (Prx) enzymes occur in both systemic autoimmune disease and vasculitis in adulthood. Because increased oxidative stress induces vasculitis in Kawasaki disease (KD), autoimmunity to Prxs in patients with KD was investigated. The presence of antibodies to Prx 1, 2 and 4 was analyzed by ELISA and Western blot. Of 30 patients with KD, 13 (43.3%) possessed antibodies to Prx 2, whereas these antibodies were present in only 1 of 10 patients (10.0%) with sepsis (4 with purulent meningitis and 6 with septicemia). In contrast, antibodies to Prx 1 and 4 were not detected in either group. There was no significant correlation among the titers of the three antibodies. Clinical parameters were compared between anti-Prx 2-positive and -negative patients. The presence of anti-Prx 2 antibodies correlated with a longer period of fever and poor response to high-dose γ-globulin therapy in patients with KD. Anti-Prx 2-positive patients had significantly greater excretion of urinary 8-isoprostaglandin than did anti-Prx 2-negative patients. These results provide the first evidence for an antibody to Prx 2 in patients with KD. They also suggest that this antibody might serve as a marker of disease severity and be involved in the pathophysiology of vasculitis in some patients with KD.     

Features of autoantigens

The major cellular antigens recognized by autoantibodies in SLE and other systemic autoimmune diseases have been identified and characterized over the past 25 years. The pioneering studies of Eng Tan demonstrate the importance of autoantibodies as diagnostic markers. However, why certain autoantibodies, such as anti-Sm, are pathognomonic of SLE, while others are markers of othe autoimmune disease subsets, remains unanswered. This central question continues to drive much current research into the pathogenesis of SLE. Features of the autoantigens recognized by autoantibodies may provide important clues to the causes of lupus. Most autoantigens in systemic autoimmunity are multicomponent nucleoprotein complexes. These particles are encountered by the immune system as units, resulting in the tandem production of autoantibodies recognizing several components of the same complex. However, the intermolecular-intrastructural spreading of autoimmunity is regulated by mechanisms that at present are defined poorly. Also unexplained is the observation that the antigenic determinants recognized by autoantibodies are restricted and frequently correspond to active sites or functional domains. Analysis of experimental models of autoimmunity suggests that altering the structure of autoantigens, due to abnormal protein-protein interactions, hapten binding, altered degradation, or other mechanisms, could help to explain both the restricted patterns of autoantibody spreading and the selective targeting of antigenic sites. This may be a worthwhile area for further investigation of the pathogenesis of systemic autoimmune diseases.Abbreviations MCTD mixed connective tissue disease - PM/DM polymyositis / dermatomyositis - SLE Systemic lupus erythematosus - SSc systemic sclerosis - SVT simian virus 40 large T antigen     

Variable overoxidation of peroxiredoxins in human lung cells in severe oxidative stress

Peroxiredoxins (Prxs) are a group of thiol containing proteins that participate both in signal transduction and in the breakdown of hydrogen peroxide (H(2)O(2)) during oxidative stress. Six distinct Prxs have been characterized in human cells (Prxs I-VI). Prxs I-IV form dimers held together by disulfide bonds, Prx V forms intramolecular bond, but the mechanism of Prx VI, so-called 1-Cys Prx, is still unclear. Here we describe the regulation of all six Prxs in cultured human lung A549 and BEAS-2B cells. The cells were exposed to variable concentrations of H(2)O(2), menadione, tumor necrosis factor-alpha or transforming growth factor-beta. To evoke glutathione depletion, the cells were furthermore treated with buthionine sulfoximine. Only high concentrations (300 microM) of H(2)O(2) caused a minor increase (<28%, 4 h) in the expression of Prxs I, IV, and VI. Severe oxidant stress (250-500 microM H(2)O(2)) caused a significant increase in the proportion of the monomeric forms of Prxs I-IV; this was reversible at lower H(2)O(2) concentrations (< or =250 microM). This recovery of Prx overoxidation differed among the various Prxs; Prx I was recovered within 24 h, but recovery required 48 h for Prx III. Overall, Prxs are not significantly modulated by mild oxidant stress or cytokines, but there is variable, though reversible, overoxidation in these proteins during severe oxidant exposure.     

Analysis of peroxiredoxin decreasing oxidative stress in hypertensive aortic smooth muscle

To determine the role of peroxiredoxin (Prx) in response to oxidative stress and during hypertension in the vasculature, we identified Prx proteins and analyzed their antioxidant effects. Rat aortic smooth muscle contains all six Prxs (I-VI). Prx I, II, and VI shifted to its acidic site on two-dimensional polyacrylamide gel electrophoresis after exposure to H(2)O(2). The total expression of Prx I and VI was increased in response to H(2)O(2). The expression of Prx I, but not that of Prx II and VI, increases and the acidic form of Prx I and the sulfonic acid form of Prx (SO(3)H-Prx) are more strongly expressed in the aortic smooth muscle of hypertensive rats than in that of normotensive control rats. Prxs were also found in the mesenteric artery, heart, and kidney. The expression levels of Prx I and VI were increased in mesenteric artery, but not heart and kidney, from hypertensive rats compared with that from normotensive rats. These results suggest that Prxs play a crucial role against oxidative stress in vascular smooth muscles during hypertension.     

Oxidized human beta2-glycoprotein I: its impact on innate immune cells

Beta2-glycoprotein I (β2-GPI), an abundant 50 kDa plasma glycoprotein, is the most common target for antiphospholipid antibodies (aPLs). These autoantibodies are associated with thrombotic events in patients with anti-phospholipid antibody syndrome (APS) and systemic lupus erythematosus (SLE) and are proatherogenic. β2-GPI can also stimulate a vigorous adaptive cellular immune response in these patients. Although much is known about β2-GPI as a cofactor in autoimmune diseases, crucial information is still lacking to clarify why this abundant self plasma protein is the target of autoimmune responses. Throughout the years, a remarkable number of theories have been proposed to explain how the immune system recognises self. On the basis of a large variety of epidemiological, clinical and experimental evidence, it has been suggested that an unfortunate interplay of genetic susceptibility and environmental factors may play an important role in generating an abnormal immune response. Among the environmental factors, oxidative stress is one of the major events causing protein structural modifications, thus inducing the appearance of neo/cryptic epitopes of β2-GPI able to activate the immune system. In particular, oxidized β2-GPI is able to induce phenotypic and functional maturation of dendritic cells which represent the link between innate and adaptive immunity. Chronic activation of autoimmune reactions against this self protein modified by oxidative events may contribute to local and systemic inflammation, thus sustaining endothelial dysfunction in patients with APS, SLE and cardiovascular diseases. The role of oxidative stress in β2-GPI-mediated immune response is described in the light of our research experience and of relevant literature emerging in the field.     

Oxidatively modified autoantigens in autoimmune diseases

Free radical-mediated oxidative damage and consequent protein modification by the end products of oxidative damage are important mediators of cell toxicity and disease pathogenesis. Aldehydic products, mainly the 4-hydroxy-2-alkenals, form adducts with proteins and make them highly immunogenic. Oxidative modification of proteins has been shown to elicit antibodies in a variety of diseases including systemic lupus erythematosus (SLE), alcoholic liver disease, diabetes mellitus (DM), and rheumatoid arthritis (RA). Oxidatively modified DNA (8-oxodeoxyguanine) and low-density lipoproteins (LDL) occur in SLE, a disease in which premature atherosclerosis is a serious problem. In addition, immunization with 4-hydroxy-2-nonenal (HNE)-modified 60-kDa Ro autoantigen elicits an accelerated epitope spreading in an animal model of SLE. Advanced glycation end product (AGE) pentosidine and AGE-modified IgG have been shown to correlate with RA disease activity. Oxidatively modified glutamic acid decarboxylase is important in type 1 DM, while autoantibodies against oxidized LDL are prevalent in Behcet's disease. The fragmentation of scleroderma-specific autoantigens occurs as a result of oxidative modification and is thought to be responsible for the production of autoantibodies through the release of cryptic epitopes. In the face of overwhelming evidence for the involvement of oxidative damage in autoimmunity the administration of antioxidants is a viable untried alternative for preventing or ameliorating autoimmune disease, although results in cardiovascular disease are disappointing.     

Free radical mediated peroxidative damage in systemic lupus erythematosus

Free radicals and damage caused by these molecular species are implicated in the pathogenesis of a variety of diseases, including autoimmune. Here we have examined oxidative damage, SOD activity and autoantibodies against SOD in systemic lupus erythematosus (SLE), a multifactorial disease with autoantibody production as an universal feature. We found significantly increased amounts of conjugated dienes in the SLE patients compared to normals (mean value of 0.917 vs 0.627, p = 0.0001) and MDA formation (6.96 vs 4.17 nmoles/microl, p = 0.0006) as well as decreased SOD activity. In addition, we found autoantibodies binding SOD by both ELISA and immunoblot. The presence of anti-SOD antibodies was associated with increased free radical damage in SLE patients. Heat inactivated anti-SOD autoantibodies were able to inhibit the activity of the enzyme. We propose that the inhibition of SOD by autoantibodies is, in part, responsible for the increased free radical damage seen in the disease.     

Decreasing peroxiredoxin II expression decreases glutathione, alters cell cycle distribution, and sensitizes glioma cells to ionizing radiation and H(2)O(2)

Glioblastomas are notorious for their resistance to ionizing radiation and chemotherapy. We hypothesize that this resistance to ionizing radiation is due, in part, to alterations in antioxidant enzymes. Here, we show that rat and human glioma cells overexpress the antioxidant enzyme peroxiredoxin II (Prx II). Glioma cells in which Prx II is decreased using shRNA exhibit increased hyperoxidation of the remaining cellular Prxs, suggesting that the redox environment is more oxidizing. Of interest, decreasing Prx II does not alter other antioxidant enzymes (i.e., catalase, GPx, Prx I, Prx III, CuZnSOD, and MnSOD). Analysis of the redox environment revealed that decreasing Prx II increased intracellular reactive oxygen species in 36B10 cells; extracellular levels of H(2)O(2) were also increased in both C6 and 36B10 cells. Treatment with H(2)O(2) led to a further elevation in intracellular reactive oxygen species in cells where Prx II was decreased. Decreasing Prx II expression in glioma cells also reduced clonogenic cell survival following exposure to ionizing radiation and H(2)O(2). Furthermore, lowering Prx II expression decreased intracellular glutathione and resulted in a significant decline in glutathione reductase activity, suggesting a possible mechanism for the observed increased sensitivity to oxidative insults. Additionally, decreasing Prx II expression increased cell cycle doubling times, with fewer cells distributed to S phase in C6 glioma cells and more cells redistributed to the most radiosensitive phase of the cell cycle, G2/M, in 36B10 glioma cells. These findings support the hypothesis that inhibiting Prx II sensitizes glioma cells to oxidative stress, presenting Prxs as potential therapeutic targets.     

Autoimmunity and immune system dysregulation in schizophrenia: IgGs from sera of patients hydrolyze myelin basic protein

Several different theories of schizophrenia (SCZ) were discussed; the causes of this disease are not yet clear. Using ELISA, it was shown that titers of autoantibodies against myelin basic protein (MBP) in SCZ patients are ~1.8‐fold higher than in healthy individuals but 5.0‐fold lower than in patients with multiple sclerosis. Several rigid criteria were checked to show that the MBP‐hydrolyzing activity is an intrinsic property of SCZ IgGs. Approximately 82% electrophoretically homogeneous SCZ IgGs purified using several affinity sorbents including Sepharose with immobilized MBP hydrolyze specifically only MBP but not many other tested proteins. The average relative activity of IgGs from patients with negative symptoms was 2.5‐fold higher than that of patients with positive symptoms of SCZ, and it increases with the duration of this pathology. It was shown that abzymes are the earliest statistically significant markers of many autoimmune pathologies. Our findings surmise that the immune systems of individual SCZ patients can generate a variety of anti‐MBP abzymes with different catalytic properties, which can attack MBP of the myelin‐proteolipid shell of axons. Therefore, autoimmune processes together with other mechanisms can play an important role in SCZ pathogenesis. MBP‐hydrolyzing antibodies were previously detected in the blood of 80% to 90% of patients with systemic lupus erythematosus (SLE) and multiple sclerosis (MS). In addition, some similar neuropsychiatric indicators of disease common to SLE, MS, and SCZ were described in the literature. Thus, the destruction of the myelin sheath and the production of MBP‐hydrolyzing antibodies can be a common phenomenon for some different diseases.     

Observed octameric assembly of a Plasmodium yoelii peroxiredoxin can be explained by the replacement of native “ball‐and‐socket” interacting residues by an affinity tag

Peroxiredoxins (Prxs) are ubiquitous and efficient antioxidant enzymes crucial for redox homeostasis in most organisms, and are of special importance for disease‐causing parasites that must protect themselves against the oxidative weapons of the human immune system. Here, we describe reanalyses of crystal structures of two Prxs from malaria parasites. In addition to producing improved structures, we provide normalizing explanations for features that had been noted as unusual in the original report of these structures (Qiu et al., BMC Struct Biol 2012;12:2). Most importantly, we provide evidence that the unusual octameric assembly seen for Plasmodium yoelii Prx1a is not physiologically relevant, but arises because the structure is not of authentic P. yoelii Prx1a, but a variant we designate PyPrx1a^N* that has seven native N‐terminal residues replaced by an affinity tag. This N‐terminal modification disrupts a previously unrecognized, hydrophobic “ball‐and‐socket” interaction conserved at the B‐type dimer interface of Prx1 subfamily enzymes, and is accommodated by a fascinating two‐residue “β‐slip” type register shift in the β‐strand association at a dimer interface. The resulting change in the geometry of the dimer provides a simple explanation for octamer formation. This study illustrates how substantive impacts can occur in protein variants in which native residues have been altered.     

Structural and functional regulation of eukaryotic 2-Cys peroxiredoxins including the plant ones in cellular defense-signaling mechanisms against oxidative stress

The ubiquitously distributed peroxiredoxins (Prxs) have been shown to have diverse functions in cellular defense‐signaling pathways. They have been largely classified into three Prx classes, 2‐Cys Prx, atypical 2‐Cys Prx and 1‐Cys Prx, which can be distinguished by how many Cys residues they possess and by their catalytic mechanisms. Proteins belonging to the typical 2‐Cys Prx group containing the N‐terminal peroxidatic Cys residue undergo a cycle of peroxide‐dependent oxidation to sulfenic acid and thiol‐dependent reduction during H₂O₂ catalysis. However, in the presence of high concentrations of H₂O₂ and catalytic components, including thioredoxin (Trx), Trx reductase and NADPH, the sulfenic acid can be hyperoxidized to cysteine sulfinic acid. The overoxidized 2‐Cys Prxs are slowly reduced by the action of the adenosine 5′‐triphosphate‐dependent enzyme, sulfiredoxin. Upon exposure of cells to strong oxidative or heat‐shock stress conditions, 2‐Cys Prxs change their protein structures from low‐molecular weight to high‐molecular weight complexes, which trigger their functional switching from peroxidases to molecular chaperones. The C‐terminal region of 2‐Cys Prx also plays an essential role in this structural conversion. Thus, proteins with truncated C‐termini are resistant to overoxidation and cannot regulate their structures or functions. These reactions are primarily guided by the active site peroxidatic Cys residue, which serves as an ‘H₂O₂‐sensor’ in cells. The reversible structural and functional switching of 2‐Cys Prxs provides cells with a means to adapt to external stresses by presumably activating intracellular defense‐signaling systems. In particular, plant 2‐Cys Prxs localized in chloroplasts have dynamic protein structures that undergo major conformational changes during catalysis, forming super‐complexes and reversibly attaching to thylakoid membranes in a redox‐dependent manner.     

Immunological evidence for the presence of peroxiredoxin in pea leaf peroxisomes and response to oxidative stress conditions

Peroxiredoxins (Prxs) constitute a group of thiol-specific antioxidant enzymes which are present in bacteria, yeasts, and in plant and animal cells. Although Prxs are mainly localized in the cytosol, they are also present in mitochondria, chloroplasts, and nuclei, but there is no evidence of the existence of Prxs in plant peroxisomes. Using soluble fractions (matrices) of peroxisomes purified from leaves of pea (Pisum sativum L.) plants, the immunological analysis with affinity-purified IgG against yeast Prx1 revealed the presence of an immunoreactive band of about 50 kDa. The apparent molecular mass of the peroxisomal Prx was not sensitive to oxidizing and reducing conditions what could be a mechanism of protection against the oxidative environment existing in peroxisomes. Postembedment, EM immunocytochemical analysis with affinity-purified IgG against yeast Prx1 antibodies, confirmed that this protein was present in the peroxisomal matrix, mitochondria, and chloroplasts. In pea plants grown under oxidative stress conditions, the protein level of peroxisomal Prx was differentially modulated, being slightly induced by growth of plants with 50 µM CdCl₂, but being significantly reduced by treatment with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The presence in the matrix of peroxisomes of a protein immunorelated to Prx of about 50 kDa, which is in the range of molecular mass of the dimeric form of other Prxs, opens new questions on the molecular properties of Prxs, but also on their function in the metabolism of reactive oxygen and nitrogen species (ROS/RNS) in these plant cell organelles, where they could be involved in the regulation of hydrogen peroxide and/or peroxynitrite.     

Clinical and immunological aspects of autoantibodies to RA33/hnRNP-A/B proteins — A link between RA,SLE and MCTD

Heterogeneous nuclear ribonucleoprotein (hnRNP) complexes are major constituents of the spliceosome. They are composed of approximately 30 different proteins which can bind to nascent pre-mRNA. Among these, the hnRNP-A/B proteins form a subgroup of highly related proteins consisting of two adjacent RNA binding domains (RBD) within the N-terminal parts, whereas the C-terminal halves contain almost 50% glycine residues. These proteins, in particular A2/RA33, are targeted by autoantibodies from patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD). In SLE anti-hnRNP antibodies frequently occur together with antibodies to U1 small nuclear RNP (U1-snRNP) and Sm, other proteins of the spliceosome. Preliminary epitope mapping studies have revealed major antibody binding sites in the RNA binding regions for all three diseases. Nevertheless, there is some indication of disease specific epitope recognition. Studies in animal models have demonstrated anti-RA33/hnRNP-A/B antibodies in lupus-prone mouse strains.Thus, autoantibodies to the spliceosomal hnRNP-A/B proteins are a common feature of RA, SLE, and MCTD. However, these diseases differ in their reactivities to other spliceosomal proteins, especially anti-U1 snRNP and Sm. Therefore, anti-RA33/hnRNP-A/B autoantibodies are not only valuable diagnostic markers but may also allow additional insights into the pathogenesis of rheumatic autoimmune diseases.Abbreviations AS ankylosing spondylitis - hnRNP heterogeneous nuclear ribonucleoprotein - MCTD mixed connective tissue disease - PSA psoriatic arthropathy - RA rheumatoid arthritis - RBD RNA binding domain - SLE systemic lupus erythematosus - snRNP small nuclear ribonucleoprotein     

Autoreactive T‐cell receptor (Vβ/D/Jβ) sequences in diabetes are homologous to insulin,glucagon, the insulin receptor,and the glucagon receptor

The hypervariable (Vβ/D/Jβ) regions of T‐cell receptors (TCR) have been sequenced in a variety of autoimmune diseases by various investigators. An analysis of some of these sequences shows that TCR from both human diabetics and NOD mice mimic insulin, glucagon, the insulin receptor, and the glucagon receptor. Such similarities are not found in the TCR produced in other human autoimmune diseases. These data may explain how insulin, glucagon, and their receptors are targets of autoimmunity in diabetes and also suggest that TCR mimicking insulin and its receptor may be targets of anti‐insulin autoantibodies. Such intra‐systemic mimicry of self‐proteins also raises complex questions about how “self” and “nonself” are regulated during TCR production, especially in light of the complementarity of insulin for its receptor and glucagon for its receptor. The data presented here suggest that some TCR may be complementary to other TCR in autoimmune diseases, a possibility that is experimentally testable. Such complementarity, if it exists, could either serve to down‐regulate the clones bearing such TCR or, alternatively, trigger an intra‐immune system civil war between them. Copyright © 2008 John Wiley & Sons, Ltd.     

Increase in expression levels and resistance to sulfhydryl oxidation of peroxiredoxin isoforms in amyloid beta-resistant nerve cells

Peroxiredoxins (Prxs) are a ubiquitously expressed family of thiol peroxidases that reduce hydrogen peroxide, peroxynitrite, and hydroperoxides using a highly conserved cysteine. There is substantial evidence that oxidative stress elicited by amyloid beta (Abeta) accumulation is a causative factor in the pathogenesis of Alzheimer disease (AD). Here we show that Abeta-resistant PC12 cell lines exhibit increased expression of multiple Prx isoforms with reduced cysteine oxidation. Abeta-resistant PC12 cells also display higher levels of thioredoxin and thioredoxin reductase, two enzymes critical for maintaining Prx activity. PC12 cells and rat primary hippocampal neurons transfected with wild type Prx1 exhibit increased Abeta resistance, whereas mutant Prx1, lacking a catalytic cysteine, confers no protection. Using an antibody that specifically recognizes sulfinylated and sulfonylated Prxs, it is demonstrated that primary rat cortical nerve cells exposed to Abeta display a time-dependent increase in cysteine oxidation of the catalytic site of Prxs that can be blocked by the addition of the thiol-antioxidant N-acetylcysteine. In support of previous findings, expression of Prx1 is higher in post-mortem human AD cortex tissues than in age-matched controls. In addition, two-dimensional gel electrophoresis and mass spectrometry analysis revealed that Prx2 exists in a more oxidized state in AD brains than in control brains. These findings suggest that increased Prx expression and resistance to sulfhydryl oxidation in Abeta-resistant nerve cells is a compensatory response to the oxidative stress initiated by chronic pro-oxidant Abeta exposure.     

IL2/IL21 region polymorphism influences response to rituximab in systemic lupus erythematosus patients

To determine whether the IL2/IL21 region, a general autoimmunity locus, contributes to the observed variation in response to rituximab in patients with systemic lupus erythematosus as well as to analyze its influence in a cohort including other autoimmune diseases. rs6822844 G/T polymorphism at the IL2–IL21 region was analyzed by TaqMan assay in 84 systemic lupus erythematosus (SLE) and 60 different systemic autoimmune diseases Spanish patients receiving rituximab. Six months after the first infusion patients were classified, according to the EULAR criteria, as good responders, partial responders and non-responders. A statistically significant difference was observed in GG genotype frequency between responder (total and partial response) (83.56 %) and non-responder (45.45 %) SLE patients (p = 0.010, odds ratio (OR) = 6.10 [1.28–29.06]). No association with the response was evident in the group of patients with autoimmune diseases other than lupus. Furthermore, when both groups of patients were pooled in a meta-analysis, a reduced statistical significance of the association was observed (p = 0.024, OR = 3.53 [1.06–11.64]). Our results show for a first time that IL2–IL21 region seems to play a role in the response to rituximab in SLE patients but not in other autoimmune diseases.     

DNA-hydrolysing activity of IgG antibodies from the sera of patients with schizophrenia

It is believed that damage to the membranes of brain cells of schizophrenia (SCZ) patients induces the formation of autoantigens and autoantibodies. Nevertheless, the importance of immunological changes leading to the loss of tolerance to self-antigens in the genesis of SCZ has not been established. The MALDI mass spectra of the IgG light chains of 20 healthy donors were relatively homogeneous and characterized by one peak with only one maximum. In contrast to the healthy donors, the MALDI mass spectra of IgG light chains corresponding to 20 SCZ patients demonstrated, similarly to 20 autoimmune systemic lupus erythematosus (SLE) patients, two maxima of a comparable intensity. In addition, the MALDI spectra of the IgG light chains of five SLE and four SCZ patients contained a small additional brightly pronounced peak with remarkably lower molecular mass compared with the main one. DNase autoantibodies (abzymes) can be found in the blood of patients with several autoimmune diseases, while the blood of healthy donors or patients with diseases without a significant disturbance of the immune status does not contain DNase abzymes. Here, we present the first analysis of anti-DNA antibodies and DNase abzymes in the sera of SCZ patients. Several strict criteria have been applied to show that the DNase activity is an intrinsic property of IgGs from the sera of SCZ patients. The sera of approximately 30% of SCZ patients displayed a higher content of antibodies (compared with 37% of SLE) interacting with single- and double-stranded DNA compared with healthy donors. Antibodies with DNase activity were revealed in 80% of the patients. These data indicate that some SCZ patients may show signs of typical autoimmune processes to a certain extent.     

Reduction of cysteine sulfinic acid by sulfiredoxin is specific to 2-cys peroxiredoxins

Cysteine residues of certain peroxiredoxins (Prxs) undergo reversible oxidation to sulfinic acid (Cys-SO2H) and the reduction reaction is catalyzed by sulfiredoxin (Srx). Specific Cys residues of various other proteins are also oxidized to sulfinic acid, suggesting that formation of Cys-SO2H might be a novel posttranslational modification that contributes to regulation of protein function. To examine the susceptibility of sulfinic forms of proteins to reduction by Srx, we prepared such forms of all six mammalian Prx isoforms and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Purified sulfiredoxin reduced the sulfinic forms of the four 2-Cys members (Prx I to Prx IV) of the Prx family in vitro, but it did not affect those of Prx V, Prx VI, or GAPDH. Furthermore, Srx bound specifically to the four 2-Cys Prxs in vitro and in cells. Sulfinic forms of Prx I and Prx II, but not of Prx VI or GAPDH, present in H2O2-treated A549 cells were gradually reduced after removal of H2O2; overexpression of Srx increased the rate of the reduction of Prx I and Prx II but did not induce that of Prx VI or GAPDH. These results suggest that reduction of Cys-SO2H by Srx is specific to 2-Cys Prx isoforms. For proteins such as Prx VI and GAPDH, sulfinic acid formation might be an irreversible process that causes protein damage.