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PubMed2004

Functional properties of the alternative NADH:ubiquinone oxidoreductase from E. coli through comparative 3-D modelling.

The alternative NADH:ubiquinone oxidoreductase (NDH-2) from Escherichia coli is a membrane protein playing a prominent role in respiration by linking the reduction of NADH to the quinone pool. Remote sequence similarity reveals an evolutionary relation between alternative NADH:quinone oxidoreductases and the SCOP-family "FAD/NAD-linked reductases". We have created a structural model for NDH-2 from E. coli through comparative modelling onto a template from this family. Combined analysis of our model and sequence conservation allowed us to include the cofactor FAD and the substrate NADH in atomic detail. Furthermore, we propose the most plausible orientation of NDH-2 relative to the membrane and specify a region of the protein potentially involved in ubiquinone binding.

Amino Acid Sequence↗

PubMed2006

A novel member of the protein disulfide oxidoreductase family from Aeropyrum pernix K1: structure, function and electrostatics.

The formation of disulfide bonds between cysteine residues is a rate-limiting step in protein folding. To control this oxidative process, different organisms have developed different systems. In bacteria, disulfide bond formation is assisted by the Dsb protein family; in eukarya, disulfide bond formation and rearrangement are catalyzed by PDI. In thermophilic organisms, a potential key role in disulfide bond formation has recently been ascribed to a new cytosolic Protein Disulphide Oxidoreductase family whose members have a molecular mass of about 26 kDa and are characterized by two thioredoxin folds comprising a CXXC active site motif each. Here we report on the functional and structural characterization of ApPDO, a new member of this family, which was isolated from the archaeon Aeropyrum pernix K1. Functional studies have revealed that ApPDO can catalyze the reduction, oxidation and isomerization of disulfide bridges. Structural studies have shown that this protein has two CXXC active sites with fairly similar geometrical parameters typical of a stable conformation. Finally, a theoretical calculation of the cysteine pK(a) values has suggested that the two active sites have similar functional properties and each of them can impart activity to the enzyme. Our results are evidence of functional similarity between the members of the Protein Disulphide Oxidoreductase family and the eukaryotic enzyme PDI. However, as the different three-dimensional features of these two biological systems strongly suggest significantly different mechanisms of action, further experimental studies will be needed to make clear how different three-dimensional structures can result in systems with similar functional behavior.

Aeropyrum↗

PubMed2005

Benzothiadiazole inhibits mitochondrial NADH:ubiquinone oxidoreductase in tobacco.

An inducer of acquired disease resistance in plants, benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester, exhibited direct, concentration-dependent inhibition of the NADH:ubiquinone oxidoreductase activity of complex I of the mitochondrial electron transport chain of cultured tobacco cells. The complex I activity was less sensitive to inhibition by salicylic acid, an endogenous activator of acquired disease resistance. Using a dichlorodihydrofluorescein assay, it was found that benzothiadiazole, salicylic acid and the complex I inhibitor rotenone, increased reactive oxygen species production within cells in a concentration-dependent manner. The results indicate that both benzothiadiazole and salicylic acid affect the mitochondria of treated plant cells and result in increased production of reactive oxygen species. The biochemical basis of this response could be related to the inhibition of the NADH:ubiquinone oxidoreductase activity of complex I that results in channelling of electrons via complex II, with concomitant higher levels of superoxide production.

Cells, Cultured↗

PubMed1999

Modulation of oxidative phosphorylation of human kidney 293 cells by transfection with the internal rotenone-insensitive NADH-quinone oxidoreductase (NDI1) gene of Saccharomyces cerevisiae.

In contrast to the mitochondrial proton-translocating NADH-quinone oxidoreductase (complex I), which consists of at least 43 different subunits, the internal rotenone-insensitive NADH-quinone oxidoreductase (Ndi1) of Saccharomyces cerevisiae is a single polypeptide enzyme. The NDI1 gene was stably transfected into the human embryonal kidney 293 (HEK 293) cells. The transfected NDI1 gene was then transcribed and translated in the HEK 293 cells to produce the functional enzyme. The immunochemical and immunofluorescence analyses indicated that the expressed Ndi1 polypeptide was located to the inner mitochondrial membranes. The expression of Ndi1 did not alter the content of existing complex I in the HEK 293 mitochondria, suggesting that the expressed Ndi1 enzyme does not displace the endogenous complex I. The NADH oxidase activity of the NDI1-transfected HEK 293 cells was not affected by rotenone but was inhibited by flavone. The ADP/O ratios coupled to NADH oxidation were lowered from 2.4 to 1.8 by NDI1-transfection while the ADP/O ratios coupled to succinate oxidation (1.6) were not changed. The NDI1-transfected HEK 293 cells were able to grow in media containing a complex I inhibitor such as rotenone and 1-methyl-4-phenylpyridinium ion. The potential usefulness of incorporating the Ndi1 protein into mitochondria of human cells is discussed.

Adenosine Triphosphate↗

PubMed2000

Role of NAD(P)H:quinone oxidoreductase 1 (DT diaphorase) in protection against quinone toxicity.

NQO1-/- mice, along with Chinese hamster ovary (CHO) cells, were used to determine the in vivo role of NAD(P)H:quinone oxidoreductase 1 (NQO1) in cellular protection against quinone cytotoxicity, membrane damage, DNA damage, and carcinogenicity. CHO cells permanently expressing various levels of cDNA-derived P450 reductase and NQO1 were produced. Treatment of CHO cells overexpressing P450 reductase with menadione, benzo[a]pyrene-3,6-quinone (BPQ), and benzoquinone led to increased cytotoxicity as compared with CHO cells expressing endogenous P450 reductase. In a similar experiment, overexpression of NQO1 significantly protected CHO cells against the cytotoxicity of these quinones. Knockout (NQO1-/-) mice deficient in NQO1 protein and activity had been generated previously in our laboratory and were used in the present studies. Wild-type (NQO1+/+) and knockout (NQO1-/-) mice were given i.p. injections of menadione and BPQ, followed by analysis of membrane damage and DNA damage. Both menadione and BPQ induced lipid peroxidation in hepatic and non-hepatic tissues, indicating increased membrane damage. Exposure to BPQ also resulted in increased hepatic DNA adducts in NQO1-/- mice as compared with NQO1+/+ mice. The skin application of BPQ alone and BPQ + 12-O-tetradecanoylphorbol-13-acetate (TPA) failed to induce papillomas, or other lesions, for up to 50 weeks in either NQO1+/+ or NQO1-/- mice. The various results from CHO cells and NQO1-/- mice indicated that NQO1 protects against quinone-induced cytotoxicity, as well as DNA and membrane damage. The absence of BPQ-induced skin carcinogenicity in NQO1-/- mice may be related to the strain (C57BL/6) of mice used in the present study and/or due to poor BPQ absorption into the skin and/or due to detoxification of BPQ by cytosolic NRH:quinone oxidoreductase 2 (NQO2).

Animals↗

PubMed1999

Coordinated induction of the c-jun gene with genes encoding quinone oxidoreductases in response to xenobiotics and antioxidants.

Xenobiotics and antioxidants induce expression of detoxifying enzymes including NAD(P)H: quinone oxidoreductase (NQO1), NRH:quinone oxidoreductase (NQO2), and glutathione S-transferase Ya (GST Ya), presumably to provide protection to cells against electrophilic and oxidative stress. Antioxidant response elements (AREs) have been found in the promoter regions of the various detoxifying enzyme genes. An ARE is required for basal expression and induction of the various detoxifying enzyme genes in response to xenobiotics and antioxidants. In this study, we demonstrated that exposure of cells to xenobiotics [e.g. beta-naphthoflavone (beta-NF)] and antioxidants [e.g. tert-butyl hydroquinone (t-BHQ)] also induced the expression of the proto-oncogene c-jun. The induction of c-jun gene expression followed kinetics similar to the induction of NQO1 and NQO2 genes with respect to the level and time of exposure. Sequence analysis of the c-jun gene promoter revealed the presence of an ARE between nucleotides -538 and -514. The c-jun ARE was highly homologous to the AREs from genes encoding NQO1, NQO2, and GST Ya. Constructs containing the c-jun ARE and 1.7 and 4.5 kb of the c-jun promoter ligated to the chloramphenicol acetyltransferase (CAT) gene, upon transfection in human hepatoblastoma (Hep-G2) cells, expressed the CAT gene, which was inducible with beta-NF and t-BHQ. Band shift assays indicated binding of two specific nuclear protein complexes with the c-jun gene ARE. The faster running c-jun gene ARE-nuclear protein complex was specifically competed out by unlabeled NQO1 and GST Ya gene AREs. These results suggest that c-jun gene expression is coordinately induced and regulated with detoxifying enzyme genes in response to xenobiotics and antioxidants. The results also suggest involvement of an ARE-mediated mechanism of induction of c-jun gene expression. However, a comparison of fold induction of endogenous c-jun gene and transfected c-jun promoter/ARE-CAT constructs indicated involvement of another ARE upstream of the 4.5-kb promoter and/or additional mechanisms such as stabilization of c-Jun RNA in response to exposure to xenobiotics and antioxidants.

Antioxidants↗

PubMed2000

Influence of the pK(a) value of the buried, active-site cysteine on the redox properties of thioredoxin-like oxidoreductases.

Thioredoxin constitutes the prototype of the thiol-disulfide oxidoreductase family. These enzymes contain an active-site disulfide bridge with the consensus sequence Cys-Xaa-Xaa-Cys. The more N-terminal active-site cysteine is generally a strong nucleophile with an abnormal low pK(a) value. In contrast, the more C-terminal cysteine is buried and only little is known about its effective pK(a) during catalysis of disulfide exchange reactions. Here we have analyzed the pK(a) values of the active-site thiols in wild type thioredoxin and a 400-fold more oxidizing thioredoxin variant by NMR spectroscopy, using selectively (13)C(beta)-Cys-labeled proteins. We find that the effective pK(a) of the buried cysteine (pK(b)) of the variant is increased, while the pK(a) of the more N-terminal cysteine (pK(N)) is decreased relative to the corresponding pK(a) values in the wild type. We propose two empirical models which exclusively require the knowledge of pK(N) to predict the redox properties of thiol-disulfide oxidoreductases with reasonable accuracy.

Alkylation↗

PubMed1997

The Na+/e- stoichiometry of the Na+-motive NADH:quinone oxidoreductase in Vibrio alginolyticus.

A method is proposed to estimate the stoichiometries of primary Na+-pumps in intact bacterial cells. It is based on technique when the H+/e- stoichiometry is measured in the presence of protophorous uncoupler and in the absence of penetrating ions other than H+. Under these conditions, the H+ influx discharges membrane potential generated by the Na+ pump so the Na+/e- and H+/e- ratios become equal. Using this approach it is shown that the Na+/e- ratio for the Na+-motive NADH:quinone oxidoreductase of Vibrio alginolyticus is equal to 0.71 +/- 0.06. The Na+/e- stoichiometry appears to be approximately 1, provided that the contribution of the non-coupled NADH:quinone oxidoreductase, which is resistant to low HQNO concentrations, is taken into account.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗

PubMed1999

Quantitative structure activity relationships for the electron transfer reactions of Anabaena PCC 7119 ferredoxin-NADP+ oxidoreductase with nitrobenzene and nitrobenzimidazolone derivatives: mechanistic implications.

The steady state single electron reduction of polynitroaromatics by ferredoxin-NADP+ oxidoreductase (EC 1.18.1.2) from cyanobacterium Anabaena PCC 7119 has been studied and quantitative structure activity relationships are described. The solubility of the polynitroaromatics as well as their reactivity towards ferredoxin-NADP+ oxidoreductase are markedly higher than those for previously studied mononitroaromatics and this enabled the independent measurement of the kinetic parameters-k(cat) and Km. Interestingly, the natural logarithm of the bimolecular rate constant, k(cat)/Km, and also the natural logarithm of k(cat) correlate with the calculated energy of the lowest unoccupied molecular orbital of the polynitroaromatic substrates. The minimal kinetic model in line with these quantitative structure activity relationships is a ping-pong mechanism which includes substrate binding equilibria in the second half reaction.

Anabaena↗

PubMed1981

Purification of 20 alpha-hydroxysteroid oxidoreductase from bovine fetal erythrocytes.

NADPH-dependent 20 alpha-hydroxysteroid oxidoreductase (20 alpha-HSD; EC 1.1.1.149) from bovine fetal erythrocytes was obtained for the first time free of hemoglobin by a new 2,500-fold purification scheme. This was achieved by a sequence of calcium phosphate gel absorption, ammonium sulfate fractionation, and affinity chromatography. The present results lead us to believe that the NADPH-dependent 3 beta-hydroxysteroid oxidoreductase activity, which was co-purified with 20 alpha-activity, may originate at the active site of 20 alpha-HSD (2).

20-Hydroxysteroid Dehydrogenases↗

PubMed2003

Cloning and expression of the ccdA-associated thiol-disulfide oxidoreductase (catA) gene from Brevibacillus choshinensis: stimulation of human epidermal growth factor production.

Brevibacillus choshinensis (Bacillus brevis) is a protein-hyperproducing bacterium with a useful host-vector system for the production of recombinant proteins. Here, we cloned the ccdA-catA (cmacr;cdA āssociated thioredoxin-like tmacr;hiol-disulfide oxidoreductase) locus of B. choshinensis HPD31-S5. CatA protein (molecular weight, 19664) contains a thioredoxin-like motif, Cys-Gly-Pro-Cys. It was successfully expressed in B. choshinensis extracellularly ( approximately 100 microg x ml(-1) culture) using the secretion vector pNCMO2, and in Escherichia coli intracellularly ( approximately 350 microg x ml(-1) culture) with an amino-terminal His-tag. Both recombinant proteins showed thiol-disulfide oxidoreductase activity. Incubation of non-native human epidermal growth factor (hEGF) containing incorrect disulfide bonds with B. choshinensis cells secreting CatA protein resulted in the stimulation of the conversion of non-native hEGF to the native form. Furthermore, co-expression of CatA protein with recombinant hEGF in the B. choshinensis production system increased the yield of native hEGF.

Amino Acid Sequence↗

PubMed1997

Drosophila melanogaster NADPH-cytochrome P450 oxidoreductase: pronounced expression in antennae may be related to odorant clearance.

Insects perceive a large number of airborne chemicals as olfactory components mainly through the antenna. It is thought that detection of the odorants by specific receptors is followed by a degradative pathway that clears the olfactory organ from accumulating chemicals. In Drosophila, a number of P450 monooxygenases are involved in the metabolism of foreign chemicals [Dunkov et al. (1996) Cytochrome P450 gene cluster in Drosophila melanogaster, Mol. Gen. Genet. 251, 290-297]. NADPH-cytochrome P450 oxidoreductases serve to transfer reducing equivalents to P450 monooxygenases. We isolated cDNA and genomic clones coding for a Drosophila NADPH cytochrome P450 oxidoreductase (CPR). The largest cDNA of 2471 nucleotides in length contained an open reading frame of 693 amino acids that includes the putative CPR sequence. CPR is a single copy gene as shown by genomic Southern hybridisation and maps to the cytogenetic map position 26C on the second chromosome. Comparison of genomic and cDNA CPR sequences revealed a gene structure that is split into at least six exons. The CPR protein sequence is almost identical with that of house fly and remarkably conserved when compared to vertebrates and yeast. RNA expression is high in embryos and antennae as compared to adult heads, adult bodies and larvae. High expression in antennae may reflect the putative function in olfactory clearance.

Amino Acid Sequence↗

PubMed2000

Regulation of genes encoding NAD(P)H:quinone oxidoreductases.

NAD(P)H:quinone oxidoreductase (NQO1) and NRH:quinone oxidoreductase (NQO2) are flavoproteins that catalyze two-electron reduction and detoxification of quinones and its derivatives. This leads to the protection of cells against redox cycling, oxidative stress, and neoplasia. NQO1 is expressed ubiquitously in all the tissues. However, the level of expression varied among the human tissues. NQO1 gene is expressed at higher levels in several tumor tissue types, including liver and colon, as compared to normal tissues of similar origin. NQO1 gene expression is coordinately induced with other detoxifying enzyme genes in response to xenobiotics, antioxidants, oxidants, heavy metals, and radiations. Deletion mutagenesis in the NQO1 gene promoter identified several cis-elements including antioxidant response element (ARE), a basal element, and AP-2 element. ARE elements have also been found in the promoter regions of other detoxifying enzyme genes including glutathione S-transferases. ARE is essentially required for expression and coordinated induction of NQO1 and other detoxifying enzyme genes. Nuclear transcription factors Nrf2 and c-Jun bind to the ARE and activate the gene expression. The binding of Nrf2 + c-Jun to the ARE required unknown cytosolic factor(s). In addition to Nrf2 and c-Jun, other nuclear transcription factors including Nrf1, Jun-B, and Jun-D also bind to the ARE and regulate expression and induction of NQO1 gene. A hypothetical model is presented based on the available information on ARE-mediated regulation of detoxifying enzyme genes. Briefly, the Nrf2 is retained in the cytosplasm by a repressor protein Keap1 in untreated normal cells. The treatment of cells with xenobiotics and antioxidants leads to the activation of unknown cytosolic factor(s) that catalyze modification of Nrf2 and/or Keap1. The modification follows dissociation of Nrf2 and Keap1. The free Nrf2 translocates in the nucleus. Nrf2 in the nucleus heterodimerizes with c-Jun and binds to the ARE resulting in the induction of NQO1 and other ARE-regulated genes expression. The identity of cytosolic factor(s) remains unknown.

Animals↗

PubMed2000

Structure-function studies of DT-diaphorase (NQO1) and NRH: quinone oxidoreductase (NQO2).

DT-diaphorase, also referred to as NQO1 or NAD(P)H: quinone acceptor oxidoreductase, is a flavoprotein that catalyzes the two-electron reduction of quinones and quinonoid compounds to hydroquinones, using either NADH or NADPH as the electron donor. NRH (dihydronicotinamide riboside): quinone oxidoreductase, also referred to as NQO2, has a high nucleotide sequence identity to DT-diaphorase and is considered to be an isozyme of DT-diaphorase. These enzymes transfer two electrons to a quinone, resulting in the formation of a hydroquinone product without the accumulation of a dissociated semiquinone. Steady and rapid-reaction kinetic experiments have been performed to determine the reaction mechanism of DT-diaphorase. Furthermore, chimeric and site-directed mutagenesis experiments have been performed to determine the molecular basis of the catalytic differences between the two isozymes and to identify the critical amino acid residues that interact with various inhibitors of the enzymes. In addition, functional studies of a natural occurring mutant Pro-187 to Ser (P187S) have been carried out. Results obtained from these investigations are summarized and discussed.

Amino Acid Sequence↗

PubMed2003

NADH-Ubiquinone oxidoreductase: substrate-dependent oxygen turnover to superoxide anion as a function of flavin mononucleotide.

Bovine heart mitochondrial NADH-ubiquinone oxidoreductase (complex I) catalyzed NADH- and ubiquinone-1-dependent oxygen (O2) turnover to hydrogen peroxide that was stimulated by piericidin A and superoxide dismutase (SOD), but was insensitive to antimycin A, myxothiazol, and potassium cyanide. The extent of O2 consumption as a function of ubiquinone-1 did not correlate with piericidin A-sensitive rates of ubiquinone reduction. Decylubiquinone did not stimulate O2 consumption, but did initiate an SOD-sensitive cytochrome c reduction when complex I was isolated away from ubiquinol-cytochrome c oxidoreductase. Rates and extent of O2 turnover (ROS production) and ubiquinone reduction were higher than previously reported for submitochondrial particles (SMP) and isolated complex I. This ROS production was shown to co-isolate with complex I flavin.

Journal Article↗

PubMed1992

Redox properties of electron-transfer flavoprotein ubiquinone oxidoreductase as determined by EPR-spectroelectrochemistry.

We have determined the formal potential values for each electron transfer to electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO), in order to further characterize the thermodynamics of electron transport from various acyl-CoA thioesters to the mitochondrial ubiquinone pool. ETF-QO contains one [4Fe-4S]2+,1+ cluster and one FAD prosthetic group. A preliminary visible-spectroelectrochemical titration showed that the two redox centers were reduced almost simultaneously. Since the visible spectra of the chromophores overlap, it was not possible to resolve the formal potential value for each electron transfer to the protein using this method. Accordingly, an EPR-spectroelectrochemical cell was designed so that each formal potential value could be resolved by EPR quantitation of the flavin semiquinone and the reduced iron-sulfur cluster during the titration. The formal potential values for electron transfer to ETF-ubiquinone oxidoreductase at pH 7.5 and 4 degrees C were E1 degrees' = +0.028 V and E2 degrees' = -0.006 V for the first and second electron transfers, respectively, to the FAD and E degrees' = +0.047 V for the iron-sulfur cluster. The thermodynamics of electron transport from the acyl-CoA substrates of beta-oxidation to the mitochondrial electron transport chain have been fully resolved with completion of this work. The results are discussed in terms of their significance to the overall electron transport process from beta-oxidation.

Acyl Coenzyme A↗

PubMed1987

NADH-ubiquinone oxidoreductases of the Escherichia coli aerobic respiratory chain.

Deamino-NADH/ubiquinone 1 oxidoreductase activity in membrane preparations from Escherichia coli GR19N is 20-50% of NADH/ubiquinone 1 oxidoreductase activity. In comparison, membranes from E. coli IY91, which contain amplified levels of NADH dehydrogenase, exhibit about 100-fold higher NADH/ubiquinone 1 reductase activity but about 20-fold less deamino-NADH/ubiquinone 1 reductase activity. Deamino-NADH/ubiquinone 1 reductase is more sensitive than NADH/ubiquinone 1 reductase activity to inhibition by 3-undecyl-2-hydroxyl-1,4-naphthoquinone, piericidin A, or myxothiazol. Furthermore, GR19N membranes exhibit two apparent Kms for NADH but only one for deamino-NADH. Inside-out membrane vesicles from E. coli GR19N generate a H+ electrochemical gradient (interior positive and acid) during electron transfer from deamino-NADH to ubiquinone 1 that is large and stable relative to that observed with NADH as substrate. Generation of the H+ electrochemical gradient in the presence of deamino-NADH is inhibited by 3-undecyl-2-hydroxy-1,4-naphthoquinone and is not observed in IY91 membrane vesicles or in vesicles from GR19N that are deficient in deamino-NADH/ubiquinone 1 reductase activity. The data provide a strong indication that the E. coli aerobic respiratory chain contains two species of NADH dehydrogenases: (i) an enzyme (NADH dh I) that reacts with deamino-NADH or NADH whose turnover leads to generation of a H+ electrochemical gradient at a site between the primary dehydrogenase and ubiquinone and (ii) an enzyme (NADH dh II) that reacts with NADH exclusively whose turnover does not lead to generation of a H+ electrochemical gradient between the primary dehydrogenase and ubiquinone 1.

Aerobiosis↗

PubMed2005

Contributions of cysteine residues in Zn2 to zinc fingers and thiol-disulfide oxidoreductase activities of chaperone DnaJ.

Escherichia coli DnaJ, possessing both chaperone and thiol-disulfide oxidoreductase activities, is a homodimeric Hsp40 protein. Each subunit contains four copies of a sequence of -CXXCXGXG-, which coordinate with two Zn(II) ions to form an unusual topology of two C4-type zinc fingers, C144DVC147Zn(II)C197NKC200 (Zn1) and C161PTC164Zn(II)C183PHC186 (Zn2). Studies on five DnaJ mutants with Cys in Zn2 replaced by His or Ser (C183H, C186H, C161H/C183H, C164H/183H, and C161S/C164S) reveal that substitutions of one or two Cys residues by His or Ser have little effect on the general conformation and association property of the molecule. Replacement of two Cys residues by His does not interfere with the zinc coordination. However, replacement of two Cys by Ser results in a significant decrease in the proportion of coordinated Zn(II), although the unique zinc finger topology is retained. The mutants of C183H, C186H, and C161S/C164S display full disulfide reductase activity of wild-type DnaJ, while C161H/C183H and C164H/183H exhibit severe defect in the activity. All of the mutations do not substantially affect the chaperone activity. The results indicate that the motif of -CXXC- is critical to form an active site and indispensable to the thiol-disulfide oxidoreductase activity of DnaJ. Each -CXXC- motif in Zn2 but not in Zn1 functions as an active site.

Amino Acid Motifs↗