Redox-regulated Proteins Research Articles

Protein Thiol Modifications Visualized In Vivo

Thiol-disulfide interconversions play a crucial role in the chemistry of biological systems. They participate in the major systems that control the cellular redox potential and prevent oxidative damage. In addition, thiol-disulfide exchange reactions serve as molecular switches in a growing number of redox-regulated proteins. We developed a differential thiol-trapping technique combined with two-dimensional gel analysis, which in combination with genetic studies, allowed us to obtain a snapshot of the in vivo thiol status of cellular proteins. We determined the redox potential of protein thiols in vivo, identified and dissected the in vivo substrate proteins of the major cellular thiol-disulfide oxidoreductases, and discovered proteins that undergo thiol modifications during oxidative stress. Under normal growth conditions most cytosolic proteins had reduced cysteines, confirming existing dogmas. Among the few partly oxidized cytosolic proteins that we detected were proteins that are known to form disulfide bond intermediates transiently during their catalytic cycle (e.g., dihydrolipoyl transacetylase and lipoamide dehydrogenase). Most proteins with highly oxidized thiols were periplasmic proteins and were found to be in vivo substrates of the disulfide-bond-forming protein DsbA. We discovered a substantial number of redox-sensitive cytoplasmic proteins, whose thiol groups were significantly oxidized in strains lacking thioredoxin A. These included detoxifying enzymes as well as many metabolic enzymes with active-site cysteines that were not known to be substrates for thioredoxin. H2O2-induced oxidative stress resulted in the specific oxidation of thiols of proteins involved in detoxification of H2O2 and of enzymes of cofactor and amino acid biosynthesis pathways such as thiolperoxidase, GTP-cyclohydrolase I, and the cobalamin-independent methionine synthase MetE. Remarkably, a number of these proteins were previously or are now shown to be redox regulated.

Thioredoxin-1 ameliorates myosin-induced autoimmune myocarditis by suppressing chemokine expressions and leukocyte chemotaxis in mice.

Cardiac myosin-induced myocarditis is an experimental autoimmune myocarditis (EAM) model used to investigate autoimmunological mechanisms in inflammatory heart diseases and resembles fulminant myocarditis in humans. We investigated the therapeutic role of thioredoxin-1 (TRX-1), a redox-regulatory protein with antioxidant and antiinflammatory effects, in murine EAM. EAM was generated in 5-week-old male BALB/c mice by immunization with porcine cardiac myosin at days 0 and 7. Recombinant human TRX-1 (rhTRX-1), C32S/C35S mutant rhTRX-1, or saline was administered intraperitoneally every second day from day 0 to 20. In addition, rabbit anti-mouse TRX-1 serum or normal rabbit serum was administered intraperitoneally on days -1, 2, and 6. Animals were euthanized on day 21. Histological analysis of the heart showed that TRX-1 significantly reduced the severity of EAM, whereas mutant TRX-1 failed to have such an effect, and anti-TRX-1 antibody enhanced the disease markedly. Immunohistochemical analysis showed that TRX-1 significantly suppressed cardiac macrophage inflammatory protein (MIP)-1alpha, MIP-2, and 8-hydroxydeoxyguanosine expression and macrophage infiltration into the heart in EAM. Although serum levels of MIP-1alpha were not suppressed by TRX-1 until day 21, both an in vitro chemotaxis chamber assay and an in vivo air pouch model showed that TRX-1 significantly suppressed MIP-1alpha- or MIP-2-induced leukocyte chemotaxis. However, real-time reverse transcription-polymerase chain reaction showed that TRX-1 failed to decrease chemokine receptor expression increased in the bone marrow cells of EAM mice. TRX-1 attenuates EAM by suppressing chemokine expressions and leukocyte chemotaxis in mice.

Differentiation-associated redox-regulation in human B cell lines from stem cell/pro-B to plasma cell

Redox-regulation of receptors and transcription factors are important for lymphocyte activation, differentiation and apoptosis. Thioredoxin (Trx) is a key redox-regulating protein and oxidative stress sensor operating in synergy with Trx-reductase and protein disulfide isomerase (PDI). The expression of Trx, PDI, and the Trx-regulated transcription-factor Pax5 were analyzed in a panel of human B cell lines and were compared with that of the Bcl-2 family proteins, also redox-controlled. The panel included representative cells from various stages: FLEB14-4 (pro-B); REH and NALM-6 (pre-B); Rael and Daudi (small mature B); U-698 and NC0467.3 (B-blasts); LP-1, U-1996, and U-266 (plasma cells). We found a significant congruence and co-variation of Trx and Bcl-2 levels in the B-lineage, with high expression levels in early stages (pro-B and pre-B) and in the late stage representing terminally-differentiated plasma cells, whereas mid-stage small resting B cells showed a very low expression. PDI increased significantly in plasma-blasts and plasma cells, indicating its importance in the highly specialized immunoglobulin assembly-machinery, including disulfide-bond isomerization. Pax5 was expressed in early and mid-stages, but was silenced in terminal stages. We conclude that the high Trx and Bcl-2-expression early and late in the B cell maturation pathway reflects a redox-strategy favoring an increased survival potential of the B cells at those stages.

S-glutathionylation: from redox regulation of protein functions to human diseases.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play an integral role in the modulation of several physiological functions but can also be potentially destructive if produced in excessive amounts. Protein cysteinyl thiols appear especially sensitive to ROS/RNS attack. Experimental evidence started to accumulate recently, documenting that S-glutathionylation occurs in a number of physiologically relevant situations, where it can produce discrete modulatory effects on protein function. The increasing evidence of functional changes resulting from this modification, and the growing number of proteins shown to be S-glutathionylated both in vitro and in vivo support this contention, and confirm this as an attractive area of research. S-glutathionylated proteins are now actively investigated with reference to problems of biological interest and as possible biomarkers of human diseases associated with oxidative/nitrosative stress.

Thioredoxin system in premature and newborn biology.

Thioredoxin is an important redox protein that is ubiquitously distributed. Thioredoxin exists in dynamic equilibrium between the oxidized and reduced forms, making it an ideal redox-regulatory protein. Thioredoxin, together with thioredoxin reductase and peroxiredoxins, forms a complete redox system that is similar to the glutathione system, but with distinct and divergent functions. This review provides a brief general summary of the thioredoxin system with particular emphasis on its role in premature birth and newborn physiology and disease states. Although extensive studies have examined the role of the thioredoxin system in antioxidant defense, cell proliferation, and signal transduction, further studies are needed to understand its role in embryogenesis and development. Such studies will facilitate our understanding of how thioredoxin may modulate newborn diseases via redox regulation.

Defining the plant disulfide proteome

There is considerable interest in redox regulation and new targets for thioredoxin and glutaredoxin are now being identified. It would be of great benefit to the field to have a list of all possible candidates for redox regulation--that is all disulfide proteins in plant. We developed a simple and very powerful method for identifying proteins with disulfide bonds in vivo. In this method, free thiols in proteins are fully blocked by alkylation, following which disulfide cysteines are converted to sulfhydryl groups by reduction. Finally, proteins with sulfhydryls are isolated by thiol affinity chromatography. Our method is unique in that membrane proteins as well as water-soluble proteins are examined for their disulfide nature. By applying this method to Arabidopsis thaliana we identified 65 putative disulfide proteins, including 20 that had not previously been demonstrated to be regulated by redox state. The newly identified, possibly redox-regulated proteins include: violaxanthin de-epoxidase, two oxygen-evolving enhancer proteins, carbonic anhydrase, photosystem I reaction center subunit N, photosystem I subunit III, S-adenosyl-L-methionine carboxyl methyltransferase, guanylate kinase, and bacterial mutT homolog. Possible functions of disulfide bonding in these proteins are discussed.

Conversion of death signal into survival signal by redox signaling.

Reperfusion of ischemic myocardium produces reactive oxygen species (ROS) and results in apoptotic cell death and DNA fragmentation. Several redox-sensitive anti- and pro- apoptotic transcription factors including nuclear factor kappaB (NF-kappaB) and heterodimeric transcription factor AP-1 progressively and steadily increase in the heart as a function of the duration of ischemia and reperfusion. When the heart is adapted to ischemic stress by repeated short-term ischemia and reperfusion, NF-kappaB remains high, while AP-1 is lowered to almost baseline value. The anti-apoptotic gene Bcl-2 is downregulated in the ischemic/reperfused heart, while it is upregulated in the adapted myocardium. Cardioprotective abilities of the adapted myocardium are abolished when heart is pre-perfused with N-acetyl cysteine to scavenge ROS, suggesting a role of redox signaling. Mammalian heart is protected by several defense systems, which include, among others, the redox-regulated protein thioredoxin. Reperfusion of ischemic myocardium results in the downregulation of thioredoxin 1 (Trx 1) expression, which was upregulated in the adapted myocardium. The increased expression of Trx 1 is completely blocked with an inhibitor of Trx 1, cis-diammine-dichloroplatinum, which also abolished cardioprotection afforded by ischemic adaptation. The cardioprotective role of Trx 1 is further confirmed with transgenic mouse hearts overexpressing Trx 1. The Trx 1 mouse hearts displayed significantly improved post-ischemic ventricular recovery and reduced myocardial infarct size and apoptosis compared to the corresponding wild-type mouse hearts. The results of this study implicate a crucial role of redox signaling in transmitting anti-death signal.

Thioredoxin, a redox-regulating protein, is expressed in spontaneous myocarditis in inbred strains of mice

Redox-regulating mechanisms may be involved in the pathogenesis of aging. Thioredoxin (TRX) is a small multifunctional protein which contains a redox active sequence. Spontaneous myocarditis is often observed in aged mice. In this study, we examined the histopathology and characteristics of TRX expression in spontaneous myocarditis in inbred strains of mice. No spontaneous myocarditis was found in adult 4-week-old inbred strains of mice. High incidence of spontaneous myocarditis was found in aged 8-week-old DBA/2 mice, and low incidence was in 8-week-old BALB/c or C57BL/6 mice. The lesions, limited to the right ventricle, were most severe in DBA/2 mice. TRX was upregulated, and the expression was correlated with the severity of the disease in these strains. Also, 8-hydroxy-2′-deoxyguanosine (8-OHdG), which was an established marker for oxidative stress, was concomitantly positive in necrotic lesions among them. In addition, the long-term anti-oxidant treatment with N-acetylcysteine (NAC) suppressed the development of spontaneous myocarditis. Thus, TRX may be induced by the spontaneously developed myocarditis, and the redox-regulating system may play an important role in the development of aging-related myocarditis.

Protective roles of thioredoxin, a redox-regulating protein, in renal ischemia/reperfusion injury

Thioredoxin (TRX) is a small protein with redox-regulating functions. Although TRX is known to be induced in response to various forms of oxidative stress, including ischemia/reperfusion injury, the induction and the specific role of this protein in the kidney have not been fully investigated. Renal ischemia/reperfusion was induced by the clipping and release of renal arteries in C57BL/6 and human thioredoxin-overexpressing transgenic (hTRX-Tg) mice. TRX protein was detected by immunohistochemistry, Western blotting, and enzyme-linked immunosorbent assay (ELISA). TRX mRNA was detected by in situ hybridization and Northern blotting. Renal functions were evaluated by measuring the levels of blood urea nitrogen and serum creatinine in these mice. With ischemia/reperfusion, endogenous murine TRX was rapidly depleted from the cytosol in the cortical proximal tubuli and detected in the urinary lumen, whereas it was spread diffusely in all segments of the tubular epithelial cells in sham-operated mice. The urinary excretion of TRX increased transiently after ischemia/reperfusion and recovered to the control level in 72 hours. In the medullary thick ascending limb (mTAL), however, TRX was specifically retained in the cytosol. A similar distribution change of transgenic hTRX was observed in the kidney of hTRX-Tg. These hTRX-Tg mice were more resistant to the injury to the mTAL and functional deterioration caused by ischemia/reperfusion, compared with wild-type mice. The present findings suggest that TRX is retained in mTAL and secreted from proximal tubuli into urine during renal ischemia/reperfusion. The mTAL-specific retention of TRX may have a protective effect against renal ischemia/reperfusion injury.

Identification of Three Previously Unknown in Vivo Protein Phosphorylation Sites in Thylakoid Membranes of Arabidopsis thaliana

The proteins in plant photosynthetic thylakoid membranes undergo light-induced phosphorylation, but only a few phosphoproteins have been characterized. To access the unknown sites of in vivo protein phosphorylation the thylakoid membranes were isolated from Arabidopsis thaliana grown in normal light, and the surface-exposed peptides were cleaved from the membranes by trypsin. The peptides were methylated and subjected to immobilized metal affinity chromatography, and the enriched phosphopeptides were sequenced using tandem nanospray quadrupole time-of-flight mass spectrometry. Three new phosphopeptides were revealed in addition to the five known phosphorylation sites in photosystem II proteins. All phosphopeptides are found phosphorylated at threonine residues implementing a strict threonine specificity of the thylakoid kinases. For the first time protein phosphorylation is found in photosystem I. The phosphorylation site is localized to the first threonine in the N terminus of PsaD protein that assists in the electron transfer from photosystem I to ferredoxin. A new phosphorylation site is also revealed in the acetylated N terminus of the minor chlorophyll a-binding protein CP29. The third novel phosphopeptide, composed of 25 amino acids, belongs to a nuclear encoded protein annotated as "expressed protein" in the Arabidopsis database. The protein precursor has a chloroplast-targeting peptide followed by the mature protein with two transmembrane helices and a molecular mass of 14 kDa. This previously uncharacterized protein is named thylakoid membrane phosphoprotein of 14 kDa (TMP14). The finding of the novel phosphoproteins extends involvement of the redox-regulated protein phosphorylation in photosynthetic membranes beyond the photosystem II and its light-harvesting antennae.

Thioredoxin-dependent redox regulation of the antioxidant responsive element (ARE) in electrophile response.

Thioredoxin is a redox-regulating protein, the expression of which is induced by various forms of oxidative stress. Thioredoxin controls the interactions of various transcription factors through redox regulation. In K562 cells, we have previously reported that hemin induces activation of the thioredoxin gene by regulating NF-E2-related factor (Nrf2) through the antioxidant responsive element (ARE). We showed here that tert-butylhydroquinone (tBHQ), an electrophile stressor, activates the thioredoxin gene through the ARE. In an electrophoretic mobility shift assay, a specific Nrf2/small Maf binding complex was induced by tBHQ and bound to the ARE. Overexpression of Nrf2 increased the tBHQ-induced thioredoxin gene activation through the ARE, whereas that of Jun and Fos suppressed the activation. The tBHQ-induced ARE binding activity was completely abrogated by an oxidizing agent, diamide, whereas 2-mercaptoethanol (2-ME) reversibly recovered the inhibitory effects of diamide, suggesting that ARE binding activity is redox-dependent. Moreover, overexpression of thioredoxin enhanced the ARE-mediated thioredoxin gene activation by tBHQ. Therefore, ARE-mediated induction of thioredoxin expression is a mechanism of enhancing signal transduction through the ARE in electrophile-induced stress responses.

Elevated serum levels of thioredoxin in patients with acute exacerbation of asthma

The pathogenesis of bronchial asthma is chronic airway inflammation caused by immune cells such as T lymphocytes and eosinophils. Eosinophils release cytotoxic products including reactive oxygen species at the site of inflammation, leading to epithelial damage. Human thioredoxin (TRX), a redox-regulating protein with antioxidant activity, is induced and secreted from cells by oxidative stress. This study was undertaken to investigate the clinical significance of TRX in the pathogenesis of asthma. We collected blood samples from 48 patients with bronchial asthma with or without attack, and measured serum ECP and pulmonary function as well as serum TRX. The serum TRX levels in patients with asthma were significantly increased in patients with mild (34.63 [28.40–42.73] ng/ml, medians with 25 and 75% interquartiles, P=0.0064) and moderate (38.83 [35.14–50.80] ng/ml, P=0.0017) asthma attacks compared with those during the asymptomatic period. The serum TRX levels were inversely correlated with FEV 1.0% ( r=−0.44, P=0.039) and %PEF ( r=−0.49, P=0.020) during attack. There was a significant correlation between the serum TRX and the serum eosinophil cationic protein ( rs=0.32, P=0.016). These findings suggest that serum TRX is related to the state of asthma exacerbation and allergic inflammation.

Temocapril treatment ameliorates autoimmune myocarditis associated with enhanced cardiomyocyte thioredoxin expression.

Thioredoxin (TRX) is a redox regulatory protein that protects cells from various stresses. Angiotensin-converting enzyme (ACE) inhibitor was reported to enhance endogenous antioxidant enzyme activities. This study was carried out to investigate whether temocapril, a novel non-sulfhydryl containing ACE inhibitor, reduces the severity of myocarditis via redox regulation mechanisms involving TRX. Western blot showed that temocapril enhanced cytosolic redox regulatory protein TRX expression, but neither mitochondrial TRX2 nor antioxidant enzymes, such as copper-zinc superoxide dismutase (Cu/Zn-SOD) or manganese superoxide dismutase (Mn-SOD) expression, was increased by the preconditioning treatment. In rats with experimental autoimmune myocarditis (EAM), the protein carbonyl content, a marker of cellular protein oxidation, was increased accompanied with enhanced TRX expression. An immunohistochemical study showed that TRX stain was enhanced in infiltrating inflammatory cells and in damaged myocytes. The severity of the myocarditis and the protein carbonyl contents were less increased in temocapril treatment (10 mg/kg/day, orally) from day 1 to day 21 in which TRX was up regulated when the inflammation started, but not in temocapril treatment from day 15-21 in which TRX was not up-regulated when the inflammation started. The results suggest that TRX and the redox state modified by TRX may play a crucial role in the pathophysiology of EAM. Temocapril ameliorates myocarditis associated with inducing TRX increase in a preconditioning manner, although the mechanism of TRX induction by temocapril remains to be elucidated.

Upregulation of redox-regulating protein, thioredoxin, in endomyocardial biopsy samples of patients with myocarditis and cardiomyopathies.

An important role of redox regulation in myocardial diseases and heart failure has been postulated. Thioredoxin (TRX) is a redox-regulating protein. Recent studies indicated a possible association between plasma TRX concentrations and the severity of heart failure. Accordingly, we investigated the myocardial expression of TRX in patients with myocarditis and cardiomyopathies. Four cases of hypertrophic cardiomyopathy (HCM), 10 of dilated cardiomyopathy (DCM), 6 of myocarditis, and 5 of controls were studied. Right and left ventricular endomyocardial biopsy samples were obtained at the diagnostic cardiac catheterization. The samples were processed for immunohistological staining for TRX, which was done by the indirect immunoperoxidase technique. 8-hydoxy-2'-deoxyguanosine (8-OHdG), one of the major DNA base-modified products, was also detected for an established marker for oxidative stress. TRX immunoreactivity was none or trivial in control specimens. Positive TRX staining was found in 6 cases; 3 in active myocarditis and 3 in DCM. The positive staining was found in infiltrating cells and damaged myocytes in the perinecrotic lesions. Damaged myocytes were also positive for 8-OHdG All the 3 cases of DCM positive for TRX stain showed severe left ventricular hypertrophy on electrocardiogram and highly elevated left ventricular end-diastolic pressure (> 24 mmHg), suggesting the overload of oxidative stress by hemodynamic impairment. Myocardial TRX was upregulated in myocarditis and cardiomyopathies with active necrotic stage associated with DNA damage, which may reflect the oxidative stress overload in hemodynamically uncontrolled status.

Dose effect of oxidative stress on signal transduction in aging

Reactive oxygen species (ROS) during normal metabolism signal cells to stimulate proliferation or to cause cellular damages, depending on a specific concentration. Energy restriction (ER) increases life span in animals, which can explain an effective modulator for reducing oxidative stress. Oxidative stress can result from a decrease in the protection against ROS. The deleterious effects of oxidative stress generally occur after exposure to a relatively high concentration of ROS. Alternatively, it has been suggested that a low concentration of ROS can exert important physiological roles in cellular signaling and proliferation. Signal pathways are crucial for cell survival or death. It is generally acceptable that aged cells have less response to stresses such as ROS than young cells. Oxidative stresses induce JNK and p38 kinase pathways regulated by redox regulatory proteins: thioredoxin and glutathione s-transferase, respectively. Antioxidants such as selenium block apoptosis induced by ROS through blocking apoptotic signal ASK1 and stimulating survival signal Akt activity. Old hepatocytes are more susceptible to ROS-induced apoptosis than young hepatocytes, which is associated with low expression of ERK and Akt kinases. Pharmacological inhibition of ERK and Akt activation in the young cells markedly increase their sensitivity to H 2O 2, and ER, by preventing loss of ERK and Akt activities, enhances survival of old hepatocytes to a level similar to those of young cells. Expressions of signal pathways such as survival and apoptotic signals can regulate cells’ fate and aging process. Further studies on the interaction of signal pathways may change the scientific direction of the study of aging.

Temocapril treatment ameliorates autoimmune myocarditis associated with enhanced cardiomyocyte thioredoxin expression.

Thioredoxin (TRX) is a redox regulatory protein that protects cells from various stresses. Angiotensin-converting enzyme (ACE) inhibitor was reported to enhance endogenous antioxidant enzyme activities. This study was carried out to investigate whether temocapril, a novel non-sulfhydryl-containing ACE inhibitor, reduces the severity of myocarditis via redox regulation mechanisms involving TRX. In normal rat myocytes in vitro and in vivo, Western blot showed that temocapril enhanced cytosolic redox regulatory protein TRX expression, but that neither mitochondrial TRX2 nor antioxidant enzymes, such as copper-zinc superoxide dismutase (Cu/Zn-SOD) or manganese superoxide dismutase (Mn-SOD) expression, was up-regulated by the preconditioning treatment. In rats with experimental autoimmune myocarditis (EAM), the severity of myocarditis and the protein carbonyl contents were less increased in temocapril treatment (10 mg/kg/day, orally) from day 1 to day 21, but not in temocapril treatment from day 15 to day 21. An immunohistochemical study showed that TRX stain was enhanced in infiltrating inflammatory cells and in damaged myocytes. Considering the characteristics of this model that myocardial inflammation begins around day 15 and increases until day 21, temocapril treatment for 3 weeks might be thought of as a preconditioning treatment. The results suggest that TRX and the redox state modified by TRX may play a crucial role in the pathophysiology of EAM. Temocapril ameliorates myocarditis associated with inducing TRX up-regulation in a preconditioning manner, although the mechanism of TRX up-regulation by temocapril remains to be elucidated.

Identification of albumin precursor protein, Phi AP3, and alpha-smooth muscle actin as novel components of redox sensing machinery in vascular smooth muscle cells.

Aerobic organisms are continually subjected to environmental stressors that compromise redox homeostasis and induce cellular injury. In vascular smooth muscle cells (vSMCs), the activation/repression of redox-regulated genes after environmental stress often involves protein binding to cis-acting antioxidant response elements (AREs). The present study was conducted to identify proteins that participate in redox-regulated protein binding to human c-Ha-ras and mouse glutathione S-transferase A1 AREs in vSMCs after oxidant injury. Challenge of vSMCs with 0.3 or 3 microM hydrogen peroxide, 3-methylcholanthrene, benzo[a]pyrene-7,8-diol, 3-hydroxy benzo[a]pyrene, and benzo[a]pyrene-3,6-quinone induced concentration-related increases in ARE protein binding. The profiles of ARE complex assembly were comparable, but exhibited chemical specificity. Pretreatment with 0.5 mM N-acetylcysteine inhibited activation of ARE protein binding in hydrogen peroxide-treated cells. Preparative electrophoretic mobility shift assays coupled to Western analysis identified NF-E2-related proteins 1 and 2 and JunD in complexes assembled on AREs. Polyethylenimine affinity and sequence-specific serial immobilized DNA affinity chromatography followed by N-terminal sequencing identified albumin precursor protein, phi AP3, and alpha-smooth muscle actin as members of the ARE signaling pathway. Sequence analysis of albumin protein revealed homology to the redox-regulated transcription factors Bach1 and 2, as well as cytoskeletal and molecular motor proteins. These results implicate albumin precursor protein, phi AP3, and alpha-smooth muscle actin as participants in redox sensing in vSMCs, and suggest that protein complex assembly involves interactions between leucine zipper and zinc finger transcription factors with cytoskeletal proteins.

Thioredoxin and peptide methionine sulfoxide reductase: convergence of similar structure and function in distinct structural folds.

Thioredoxin (Trx) and peptide methionine sulfoxide reductase (PMSR) are small thiol oxidoreductases implicated in antioxidant defense and redox regulation of cellular processes. Here we show that the structures of Trx and PMSR exhibit resemblance in their alphabeta core regions and that the active site cysteines in two proteins occupy equivalent positions downstream of a central beta-strand and at the N-terminus of an alpha-helix. Moreover, we identified a PMSR subfamily that contains an active site CxxC motif (two cysteines separated by two other amino acids) positioned similarly to the catalytic redox active CxxC motif in Trx. However, Trx and PMSR are characterized by distinct ancient folds that differ in both orientation of secondary structures and their patterns. Trx is a member of the Trx-fold superfamily, whereas PMSR has a unique fold not found in other proteins. The data suggest that similar structures and functions of Trx and PMSR were acquired independently during evolution and point to a general strategy of identifying new redox regulatory proteins.

Development of a sensitive assay to detect reversibly oxidized protein cysteine sulfhydryl groups.

Protein sulfhydryl groups can undergo reversible oxidation reactions in response to reactive oxygen and reactive nitrogen species. Sensitive detection of sulfhydryl group oxidation in specific proteins is required to further our understanding of protein redox changes in biological systems. In general, to detect reversible oxidation reactions the oxidized sulfur atom is reduced to a sulfhydryl group followed by a reaction with a quantifiable agent. Our aim was to develop a sensitive method to detect reversibly oxidized protein sulfhydryl groups in a Western blot format. Conjugation of methoxypolyethylene glycol-maleimide (MAL-PEG) to protein sulfhydryl groups was optimized. Once MAL-PEG forms a covalent bond with the protein, the MAL-PEG-protein conjugate can be detected as a band shift by western analysis. The efficiency of MAL-PEG conjugation to protein was determined with creatine kinase. MAL-PEG conjugated to approximately 100% of the available sulfhydryl groups on creatine kinase within 30 min. Band shift detection sensitivity was measured using the redox-regulated protein p53. MAL-PEG conjugation coupled to western analysis detected a minimum of 0.23 pmol of oxidized p53. The MAL-PEG conjugation method described in this communication can be used to assess the reversible sulfhydryl oxidation status of proteins for which antibodies suitable for western analysis are available.

Molecular views of redox regulation: three-dimensional structures of redox regulatory proteins and protein complexes.

The last decade has witnessed the explosion of research on redox-controlled cellular and biochemical processes. Whereas the vast majority of these studies have centered on clinical, genetic, and biochemical aspects of redox signaling and regulation inside and outside the cell, a significant number of nuclear magnetic resonance (NMR) and crystallographic studies have been undertaken to obtain an atomic-level understanding of the mechanisms of the redox regulation. This review highlights the recent progress of three-dimensional structure determination of key proteins and protein complexes involved in redox regulation. An increased list of such class of protein structures and their complexes with ligands will provide invaluable insight into the molecular basis of redox-regulatory processes and may be useful for the future development of therapeutic agents for redox-related diseases.