Evolution of antioxidant mechanisms: thiol-dependent peroxidases and thioltransferase among procaryotes

Redox and Thiols in Archaea

Low molecular weight (LMW) thiols have many functions in bacteria and eukarya, ranging from redox homeostasis to acting as cofactors in numerous reactions, including detoxification of xenobiotic compounds. The LMW thiol, glutathione (GSH), is found in eukaryotes and many species of bacteria. Analogues of GSH include the structurally different LMW thiols: bacillithiol, mycothiol, ergothioneine, and coenzyme A. Many advances have been made in understanding the diverse and multiple functions of GSH and GSH analogues in bacteria but much less is known about distribution and functions of GSH and its analogues in archaea, which constitute the third domain of life, occupying many niches, including those in extreme environments. Archaea are able to use many energy sources and have many unique metabolic reactions and as a result are major contributors to geochemical cycles. As LMW thiols are major players in cells, this review explores the distribution of thiols and their biochemistry in archaea.

[Biliodigestive anastomosis: indications, complications and interdisciplinary management]

Techniques for biliodigestive anastomoses are a frequent indication in primary surgical interventions. Moreover, they are required to manage secondary complications of hepatobiliary surgery. Evidence for the management of complications following biliodigestive anastomoses is low. Biliodigestive anastomoses can be performed as hepaticojejunostomy, hepatojejunostomy/portoenterostomy and hepaticoduodenostomy using running or single stitch suture techniques. Complication management in the hands of experienced hepatopancreatobiliary surgeons should consider a time delay to the primary operation and an interdisciplinary surgical and/or endoscopic or radiologic interventional approach. The therapy may be protracted and requires repeated critical reflection of the particular complication.

Glutathione in bacteria

Glutathione metabolism and its role in vital functions of bacterial cells are considered, as well as common features and differences between the functions of glutathione in prokaryotic and eukaryotic cells. Particular attention is given to the recent data for the role of glutathione in bacterial redox-regulation and adaptation to stresses.

Glutathione homeostasis and redox-regulation by sulfhydryl groups

Continuous control of metabolism and developmental processes is a key feature of live cells. Cysteine thiol residues of proteins are both exceptionally useful in terms of structural and regulatory aspects, but at the same time exceptionally vulnerable to oxidation. Conserved cysteines thus are highly important for the function of metabolic enzymes and for signaling processes underlying responses to environmental factors. The underlying mechanism for the central role of thiol-mediated redox control in cellular metabolism is the ability of the cysteine-thiols to reversibly change their redox state followed by changes of structural, catalytic or regulatory functions. The cellular glutathione/glutathione disulfide redox buffer is present in cells at millimolar concentrations and forms one major basis of redox homeostasis by which protein thiols can maintain their redox state or oxidized protein thiols can be reverted to their reduced state. Besides acting as redox buffer, glutathione also acts as an electron donor for both scavenging of reactive oxygen, e.g. from photosynthesis and respiration, and metabolic reactions such as reduction of hydroperoxides and lipidperoxides or sulfate assimilation. The central role of glutathione is further emphasized by its involvement in signaling processes and the crosstalk of redox signaling processes with other means of signaling including protein glutathionylation and control of transcription factors. The present review aims at highlighting the key functions of glutathione in thiol-mediated redox control and its interplay with other protein-thiol-based redox systems.

Coactivator MBF1 preserves the redox-dependent AP-1 activity during oxidative stress in Drosophila

Basic leucine zipper proteins Jun and Fos form the dimeric transcription factor AP-1, essential for cell differentiation and immune and antioxidant defenses. AP-1 activity is controlled, in part, by the redox state of critical cysteine residues within the basic regions of Jun and Fos. Mutation of these cysteines contributes to oncogenic potential of Jun and Fos. How cells maintain the redox-dependent AP-1 activity at favorable levels is not known. We show that the conserved coactivator MBF1 is a positive modulator of AP-1. Via a direct interaction with the basic region of Drosophila Jun (D-Jun), MBF1 prevents an oxidative modification (S-cystenyl cystenylation) of the critical cysteine and stimulates AP-1 binding to DNA. Cytoplasmic MBF1 translocates to the nucleus together with a transfected D-Jun protein, suggesting that MBF1 protects nascent D-Jun also in Drosophila cells. mbf1-null mutants live shorter than mbf1+ controls in the presence of hydrogen peroxide (H2O2). An AP-1-dependent epithelial closure becomes sensitive to H2O2 in flies lacking MBF1. We conclude that by preserving the redox-sensitive AP-1 activity, MBF1 provides an advantage during oxidative stress.

Glutathione protects Lactococcus lactis against oxidative stress

Glutathione was found in several dairy Lactococcus lactis strains grown in M17 medium. None of these strains was able to synthesize glutathione. In chemically defined medium, L. lactis subsp. cremoris strain SK11 was able to accumulate up to approximately 60 mM glutathione when this compound was added to the medium. Stationary-phase cells of strain SK11 grown in chemically defined medium supplemented with glutathione showed significantly increased resistance (up to fivefold increased resistance) to treatment with H2O2 compared to the resistance of cells without intracellular glutathione. The resistance to H2O2 treatment was found to be dependent on the accumulation of glutathione in 16 strains of L. lactis tested. We propose that by taking up glutathione, L. lactis might activate a glutathione-glutathione peroxidase-glutathione reductase system in stationary-phase cells, which catalyzes the reduction of H2O2. Glutathione reductase, which reduces oxidized glutathione, was detectable in most strains of L. lactis, but the activities of different strains were very variable. In general, the glutathione reductase activities of L. lactis subsp. lactis are higher than those of L. lactis subsp. cremoris, and the activities were much higher when strains were grown aerobically. In addition, glutathione peroxidase is detectable in strain SK11, and the level was fivefold greater when the organism was grown aerobically than when the organism was grown anaerobically. Therefore, the presence of glutathione in L. lactis could result in greater stability under storage conditions and quicker growth upon inoculation, two important attributes of successful starter cultures.

Exogenous glutathione completes the defense against oxidative stress in Haemophilus influenzae

Since they are equipped with several strategies by which they evade the antimicrobial defense of host macrophages, it is surprising that members of the genus Haemophilus appear to be deficient in common antioxidant systems that are well established to protect prokaryotes against oxidative stress. Among others, no genetic evidence for glutathione (gamma-Glu-Cys-Gly) (GSH) biosynthesis or for alkyl hydroperoxide reduction (e.g., the Ahp system characteristic or enteric bacteria) is apparent from the Haemophilus influenzae Rd genome sequence, suggesting that the organism relies on alternative systems to maintain redox homeostasis or to reduce small alkyl hydroperoxides. In this report we address this apparent paradox for the nontypeable H. influenzae type strain NCTC 8143. Instead of biosynthesis, we could show that this strain acquires GSH by importing the thiol tripeptide from the growth medium. Although such GSH accumulation had no effect on growth rates, the presence of cellular GSH protected against methylglyoxal, tert-butyl hydroperoxide (t-BuOOH), and S-nitrosoglutathione toxicity and regulated the activity of certain antioxidant enzymes. H. influenzae NCTC 8143 extracts were shown to contain GSH-dependent peroxidase activity with t-BuOOH as the peroxide substrate. The GSH-mediated protection against t-BuOOH stress is most probably catalyzed by the product of open reading frame HI0572 (Prx/Grx), which we isolated from a genomic DNA fragment that confers wild-type resistance to t-BuOOH toxicity in the Ahp-negative Escherichia coli strain TA4315 and that introduces GSH-dependent alkyl hydroperoxide reductase activity into naturally GSH peroxidase-negative E. coli. Finally, we demonstrated that cysteine is an essential amino acid for growth and that cystine, GSH, glutathione amide, and cysteinylglycine can be catabolized in order to complement cysteine deficiency.

Escherichia coli gamma-glutamylcysteine synthetase. Two active site metal ions affect substrate and inhibitor binding

Gamma-glutamylcysteine synthetase (gamma-GCS, glutamate-cysteine ligase), which catalyzes the first and rate-limiting step in glutathione biosynthesis, is present in many prokaryotes and in virtually all eukaryotes. Although all eukaryotic gamma-GCS isoforms examined to date are rapidly inhibited by buthionine sulfoximine (BSO), most reports indicate that bacterial gamma-GCS is resistant to BSO. We have confirmed the latter finding with Escherichia coli gamma-GCS under standard assay conditions, showing both decreased initial binding affinity for BSO and a reduced rate of BSO-mediated inactivation compared with mammalian isoforms. We also find that substitution of Mn2+ for Mg2+ in assay mixtures increases both the initial binding affinity of BSO and the rate at which BSO causes mechanism-based inactivation. Similarly, the specificity of E. coli gamma-GCS for its amino acid substrates is broadened in the presence of Mn2+, and the rate of reaction for some very poor substrates is improved. These results suggest that divalent metal ions have a role in amino acid binding to E. coli gamma-GCS. Electron paramagnetic resonance (EPR) studies carried out with Mn2+ show that E. coli gamma-GCS binds two divalent metal ions; Kd values for Mn2+ are 1.1 microm and 82 microm, respectively. Binding of l-glutamate or l-BSO to the two Mn2+/gamma-GCS species produces additional upfield and downfield X-band EPR hyperfine lines at 45 G intervals, a result indicating that the two Mn2+ are spin-coupled and thus apparently separated by 5 A or less in the active site. Additional EPR studies in which Cu2+ replaced Mg2+ or Mn2+ suggest that Cu2+ is bound by one N and three O ligands in the gamma-GCS active site. The results are discussed in the context of the catalytic mechanism of gamma-GCS and its relationship to the more fully characterized glutamine synthetase reaction.

Characterization of glutathione amide reductase from Chromatium gracile. Identification of a novel thiol peroxidase (Prx/Grx) fueled by glutathione amide redox cycling

Among the Chromatiaceae, the glutathione derivative gamma-l-glutamyl-l-cysteinylglycine amide, or glutathione amide, was reported to be present in facultative aerobic as well as in strictly anaerobic species. The gene (garB) encoding the central enzyme in glutathione amide cycling, glutathione amide reductase (GAR), has been isolated from Chromatium gracile, and its genomic organization has been examined. The garB gene is immediately preceded by an open reading frame encoding a novel 27.5-kDa chimeric enzyme composed of one N-terminal peroxiredoxin-like domain followed by a glutaredoxin-like C terminus. The 27.5-kDa enzyme was established in vitro to be a glutathione amide-dependent peroxidase, being the first example of a prokaryotic low molecular mass thiol-dependent peroxidase. Amino acid sequence alignment of GAR with the functionally homologous glutathione and trypanothione reductases emphasizes the conservation of the catalytically important redox-active disulfide and of regions involved in binding the FAD prosthetic group and the substrates glutathione amide disulfide and NADH. By establishing Michaelis constants of 97 and 13.2 microm for glutathione amide disulfide and NADH, respectively (in contrast to K(m) values of 6.9 mm for glutathione disulfide and 1.98 mm for NADPH), the exclusive substrate specificities of GAR have been documented. Specificity for the amidated disulfide cofactor partly can be explained by the substitution of Arg-37, shown by x-ray crystallographic data of the human glutathione reductase to hydrogen-bond one of the glutathione glycyl carboxylates, by the negatively charged Glu-21. On the other hand, the preference for the unusual electron donor, to some extent, has to rely on the substitution of the basic residues Arg-218, His-219, and Arg-224, which have been shown to interact in the human enzyme with the NADPH 2'-phosphate group, by Leu-197, Glu-198, and Phe-203. We suggest GAR to be the newest member of the class I flavoprotein disulfide reductase family of oxidoreductases.

Glutathione and glutathione-related enzymes in reproduction. A review

Glutathione and glutathione-related enzymes are pivotal for the normal functioning of several important biological processes in humans. Glutathione and glutathione-related enzymes are involved in the metabolism and detoxification of cytotoxic and carcinogenic compounds as well as reactive oxygen species. The role of reactive oxygen species in reproduction was the subject of many investigations, and there is compelling evidence for the involvement of these species in the physiology and pathology of both male and female reproductive systems. The glutathione/glutathione-related enzyme system was extensively studied in gynaecological oncology, but to a lesser extent in other topics related to reproduction. In this paper a review is provided on the glutathione/glutathione-related enzyme system in reproduction. Attention is given to its role as a detoxicating system, and as an early marker for disease.

Enterococcus faecalis glutathione reductase: purification, characterization and expression under normal and hyperbaric O2 conditions

Glutathione reductase is found ubiquitously in eukaryotes and Gram-negative bacteria, and plays a significant role in bacterial defense against oxidative stress. Glutathione reductase from the Gram-positive bacterium Enterococcus faecalis was purified to homogeneity using anion exchange, hydrophobic interaction, and affinity chromatography. The homogeneous 49-kDa enzyme contained 1 mol bound FAD per subunit. The determined N-terminal amino acid sequence of the E. faecalis enzyme displays significant identity with glutathione reductases from other Gram-negative and Gram-positive bacteria, as well as yeast and human erythrocyte reductases. The kinetic mechanism is ping-pong, and the determined kinetic parameters exhibited by the E. faecalis glutathione reductase are similar to those found for glutathione reductases from yeast, Escherichia coli, and human erythrocyte. A two-fold increased expression of glutathione reductase activity and a three-fold induction of glutathione peroxidase activity were observed under hyperbaric O2 growth conditions without a corresponding change in the total glutathione and soluble thiol content. The difference in the expression of the enzyme, and its cognate substrate's intracellular concentration, under these conditions suggest that the gene encoding glutathione reductase is responsive to oxygen concentration, but that the genes encoding the glutathione synthesizing enzymes are not linked to an oxygen-sensitive promoter.

Coenzyme A disulfide reductase, the primary low molecular weight disulfide reductase from Staphylococcus aureus. Purification and characterization of the native enzyme

The human pathogen Staphylococcus aureus does not utilize the glutathione thiol/disulfide redox system employed by eukaryotes and many bacteria. Instead, this organism produces CoA as its major low molecular weight thiol. We report the identification and purification of the disulfide reductase component of this thiol/disulfide redox system. Coenzyme A disulfide reductase (CoADR) catalyzes the specific reduction of CoA disulfide by NADPH. CoADR has a pH optimum of 7.5-8.0 and is a dimer of identical subunits of Mr 49,000 each. The visible absorbance spectrum is indicative of a flavoprotein with a lambdamax = 452 nm. The liberated flavin from thermally denatured enzyme was identified as flavin adenine dinucleotide. Steady-state kinetic analysis revealed that CoADR catalyzes the reduction of CoA disulfide by NADPH at pH 7.8 with a Km for NADPH of 2 muM and for CoA disulfide of 11 muM. In addition to CoA disulfide CoADR reduces 4,4'-diphosphopantethine but has no measurable ability to reduce oxidized glutathione, cystine, pantethine, or H2O2. CoADR demonstrates a sequential kinetic mechanism and employs a single active site cysteine residue that forms a stable mixed disulfide with CoA during catalysis. These data suggest that S. aureus employs a thiol/disulfide redox system based on CoA/CoA-disulfide and CoADR, an unorthodox new member of the pyridine nucleotide-disulfide reductase superfamily.

Distribution of thiols in microorganisms: mycothiol is a major thiol in most actinomycetes

Mycothiol [2-(N-acetylcysteinyl)amido-2-deoxy-alpha-D-glucopyranosyl- (1-->1)-myo-inositol] (MSH) has recently been identified as a major thiol in a number of actinomycetes (S. Sakuda, Z.-Y. Zhou, and Y. Yamada, Biosci. Biotech. Biochem. 58:1347-1348, 1994; H. S. C. Spies and D. J. Steenkamp, Eur. J. Biochem. 224:203-213, 1994; and G. L. Newton, C. A. Bewley, T. J. Dwyer, R. Horn, Y. Aharonowitz, G. Cohen, J. Davies, D. J. Faulkner, and R. C. Fahey, Eur. J. Biochem. 230:821-825, 1995). Since this novel thiol is more resistant than glutathione to heavy-metal ion-catalyzed oxidation, it seems likely to be the antioxidant thiol used by aerobic gram-positive bacteria that do not produce glutathione (GSH). In the present study we sought to define the spectrum of organisms that produce MSH. GSH was absent in all actinomycetes and some of the other gram-positive bacteria studied. Surprisingly, the streptococci and enterococci contained GSH, and some strains appeared to synthesize it rather than import it from the growth medium. MSH was found at significant levels in most actinomycetes examined. Among the actinobacteria four Micrococcus species produced MSH, but MSH was not found in representatives of the Arthrobacter, Agromyces, or Actinomyces genera. Of the nocardioforms examined, Nocardia, Rhodococcus, and Mycobacteria spp. all produced MSH. In addition to the established production of MSH by streptomycetes, we found that Micromonospora, Actinomadura, and Nocardiopsis spp. also synthesized MSH. Mycothiol production was not detected in Propionibacterium acnes or in representative species of the Listeria, Staphylococcus, Streptococcus, Enterococcus, Bacillus, and Clostridium genera. Examination of representatives of the cyanobacteria, purple bacteria, and spirochetes also gave negative results, as did tests of rat liver, bonito, Candida albicans, Neurospora crassa, and spinach leaves. The results, which indicate that MSH production is restricted to the actinomycetes, could have significant implications for the detection and treatment of infections with actinomycetes, especially those caused by mycobacteria.

Low-molecular-weight thiols in streptomycetes and their potential role as antioxidants

The intracellular low-molecular-weight thiols present in five gram-positive Streptomyces species and one Flavobacterium species were analyzed by high-performance liquid chromatography after fluorescence labeling with monobromobimane. Bacteria were chosen to include penicillin and cephalosporin beta-lactam producers and nonproducers. No significant amount of glutathione was found in any of the streptomycetes. Major intracellular thiols in all strains examined were cysteine, coenzyme A, sulfide, thiosulfate, and an unknown thiol designated U17. Those streptomycetes that make beta-lactam antibiotics also produce significant amounts of delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV), a key intermediate in their biosynthesis. In Streptomyces clavuligerus, a potent producer of beta-lactams, the level of ACV was low during the early phase of growth and increased rapidly toward the end of exponential growth, paralleling that of antibiotic production. These and other observations indicate that ACV does not function as a protective thiol in streptomycetes. U17 may have this role since it was the major thiol in all streptomycetes and appeared to occur at levels about 10-fold higher than those of the other thiols measured, including ACV. Purification and amino acid analysis of U17 indicated that it contains cysteine and an unusual amine that is not one of the common amino acids. This thiol is identical to an unknown thiol found previously in Micrococcus roseus and Streptomyces griseus. A high level of ergothioneine was found in Streptomyces lactamdurans, and several unidentified thiols were detected in this and other streptomycetes.

Oxygen free radicals and brain dysfunction

Oxygen free radicals, any chemical moiety containing an oxygen atom with an unpaired electron in the outer orbital shell, are generated during many normal biochemical reactions in living tissue. The unpaired electron makes these compounds highly reactive and they can initiate disruptive peroxidation reactions with various substrates important to the survival of cells such as proteins, lipids and nucleic acids. A fairly complex defense system has evolved to protect living tissue from free radicals and to minimize the damage they might cause. Neurons are especially vulnerable to free radical attack and impaired defenses or exposure to excess free radicals can lead to neuronal death. Free radicals contribute to neuronal loss in cerebral ischemia and hemorrhage and may be involved in the degeneration of neurons in epilepsy, schizophrenia, tardive dyskinesia, normal aging, Parkinson's Disease and Alzheimer's Disease. The development of drugs that limit or prevent the attack of free radicals on neurons would be an important advance in the treatment of these conditions.