Disulfide Oxidoreductase Research Articles

A Macromolecular Complex Formed by a Pilin-like Protein in Competent Bacillus subtilis

In competent Bacillus subtilis, the ComG proteins are required to allow exogenous DNA to access to membrane-bound receptor ComEA during transformation. Here we describe a multimeric complex containing the pilin-like protein ComGC. Due to similarities to the type 4 pilus and the type 2 secretion system pseudopilus, we have tentatively named it the "competence pseudopilus." The ComGC multimer is released from cells upon digestion of the cell wall with lysozyme and has a heterogeneous size, estimated to range between 40 and 100 monomers, covalently linked by disulfide bonds. We determined that the prepilin peptidase ComC, the thiol-disulfide oxidoreductase pair BdbDC, and all seven ComG proteins are necessary to form the pseudopilus. Furthermore, these proteins are also sufficient to form a functional complex, i.e. able to facilitate binding of exogenous DNA to ComEA. The initial steps of pseudopilus biogenesis include the processing of ComGC in the cytoplasmic membrane and consist of two independent events, proteolytic cleavage by ComC and formation of an intramolecular disulfide bond by BdbDC. The other ComG proteins are required to assemble the mature ComGC monomers in the membrane into a multimeric complex proposed to span the cell envelope. We discuss the possible role of the competence pseudopilus in DNA binding and uptake during transformation.

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 p K 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.

The Structure of G4, the Poxvirus Disulfide Oxidoreductase Essential for Virus Maturation and Infectivity

The possibility of the release of smallpox virus into a predominantly nonimmunized population highlights the importance of understanding poxvirus biology. Poxviruses encode a conserved pathway that is required to oxidize disulfide bonds in nascent viral proteins that fold in the reducing environment of the eukaryotic host cytoplasm. We present the structure of the last enzyme of the vaccinia virus pathway, G4, which is almost identical in smallpox virus. G4 catalyzes the formation of disulfide bonds in proteins that are critical for virus maturation and host cell infection. G4 contains a thioredoxin fold and a Cys-X-X-Cys active site. In solution, G4 monomers and dimers are observed. In the crystal, G4 is found as a dimer that buries 4,500 A(2) in the interface and occludes the active site, which could protect the reactive disulfide from reduction in the cytoplasm. The structure serves as a model for drug design targeting viral disulfide bond formation.

A Mutation in Flavobacterium psychrophilum tlpB Inhibits Gliding Motility and Induces Biofilm Formation

Flavobacterium psychrophilum is a psychrotrophic, fish-pathogenic bacterium belonging to the Cytophaga-Flavobacterium-Bacteroides group. Tn4351-induced mutants deficient in gliding motility, growth on iron-depleted media, and extracellular proteolytic activity were isolated. Some of these mutants were affected in only one of these characteristics, whereas others had defects in two or more. FP523, a mutant deficient in all of these properties, was studied further. FP523 had a Tn4351 insertion in tlpB (thiol oxidoreductase-like protein gene), which encodes a 41.4-kDa protein whose sequence does not exhibit high levels of similar to the sequences of proteins having known functions. TlpB has two domains; the N-terminal domains has five transmembrane regions, whereas the C-terminal domains has the Cys-X-X-Cys motif and other conserved motifs characteristic of thiol:disulfide oxidoreductases. Quantitative analysis of the thiol groups of periplasmic proteins revealed that TlpB is required for reduction of these groups. The tlpB gene is part of the fpt (F. psychrophilum thiol oxidoreductase) operon that contains two other genes, tlpA and tpiA, which encode a thiol:disulfide oxidoreductase and a triosephosphate isomerase, respectively. FP523 exhibited enhanced biofilm formation and decreased virulence and cytotoxicity. Complementation with the tlpB loci restored the wild-type phenotype. Gliding motility and biofilm formation appear to be antagonistic properties, which are both affected by TlpB.

One Single In-frame AUG Codon Is Responsible for a Diversity of Subcellular Localizations of Glutaredoxin 2 in Saccharomyces cerevisiae

Glutaredoxins belong to a family of small proteins with glutathione-dependent disulfide oxidoreductase activity involved in cellular defense against oxidative stress. The product of the yeast GRX2 gene is a protein that is localized both in the cytosol and mitochondria. To throw light onto the mechanism responsible for the dual subcellular distribution of Grx2 we analyzed mutant constructs containing different targeting information. By altering amino acid residues around the two in-frame translation initiation start sites of the GRX2 gene, we could demonstrate that the cytosolic isoform of Grx2 was synthesized from the second AUG, lacking an N-terminal extension. Translation from the first AUG resulted in a long isoform carrying a mitochondrial targeting presequence. The mitochondrial targeting properties of the presequence and the influence of the mature part of Grx2 were analyzed by the characterization of the import kinetics of specific fusion proteins. Import of the mitochondrial isoform is relatively inefficient and results in the accumulation of a substantial amount of unprocessed form in the mitochondrial outer membrane. Substitution of Met(35), the second translation start site, to Val resulted in an exclusive targeting to the mitochondrial matrix. Our results show that a plethora of Grx2 subcellular localizations could spread its antioxidant functions all over the cell, but one single A to G [corrected] mutation converts Grx2 into a typical protein of the mitochondrial matrix. The "A" denotes adenine, rather than alanine, and the "G" refers to guanine, not glycine [corrected]

Role of Membrane-Bound Thiol–Disulfide Oxidoreductases in Endospore-Forming Bacteria

Thiol-disulfide oxidoreductases catalyze formation, disruption, or isomerization of disulfide bonds between cysteine residues in proteins. Much is known about the functional roles and properties of this class of redox enzymes in vegetative bacterial cells but their involvement in sporulation has remained unknown until recently. Two membrane-embedded thiol-disulfide oxidoreductases, CcdA and StoA/SpoIVH, conditionally required for efficient production of Bacillus subtilis heat-resistant endospores, have now been identified. Properties of mutant cells lacking the two enzymes indicate new aspects in the molecular details of endospore envelope development. This mini-review presents an overview of membrane-bound thiol-disulfide oxidoreductases in the Gram-positive bacterium B. subtilis and endospore synthesis. Accumulated experimental findings on CcdA and StoA/SpoIVH are reviewed. A model for the role of these proteins in endospore cortex biogenesis in presented.

Crystal structure of yeast Sco1

The Sco family of proteins are involved in the assembly of the dinuclear CuA site in cytochrome c oxidase (COX), the terminal enzyme in aerobic respiration. These proteins, which are found in both eukaryotes and prokaryotes, are characterized by a conserved CXXXC sequence motif that binds copper ions and that has also been proposed to perform a thiol:disulfide oxidoreductase function. The crystal structures of Saccharomyces cerevisiae apo Sco1 (apo-ySco1) and Sco1 in the presence of copper ions (Cu-ySco1) were determined to 1.8- and 2.3-A resolutions, respectively. Yeast Sco1 exhibits a thioredoxin-like fold, similar to that observed for human Sco1 and a homolog from Bacillus subtilis. The Cu-ySco1 structure, obtained by soaking apo-ySco1 crystals in copper ions, reveals an unexpected copper-binding site involving Cys181 and Cys216, cysteine residues present in ySco1 but not in other homologs. The conserved CXXXC cysteines, Cys148 and Cys152, can undergo redox chemistry in the crystal. An essential histidine residue, His239, is located on a highly flexible loop, denoted the Sco loop, and can adopt positions proximal to both pairs of cysteines. Interactions between ySco1 and its partner proteins yeast Cox17 and yeast COX2 are likely to occur via complementary electrostatic surfaces. This high-resolution model of a eukaryotic Sco protein provides new insight into Sco copper binding and function.

The Bacillus subtilis YkuV Is a Thiol:Disulfide Oxidoreductase Revealed by Its Redox Structures and Activity

The Bacillus subtilis YkuV responds to environmental oxidative stress and plays an important role for the bacteria to adapt to the environment. Bioinformatic analysis suggests that YkuV is a homolog of membrane-anchored proteins and belongs to the thioredoxin-like protein superfamily containing the typical Cys-Xaa-Xaa-Cys active motif. However, the biological function of this protein remains unknown thus far. In order to elucidate the biological function, we have determined the solution structures of both the oxidized and reduced forms of B. subtilis YkuV by NMR spectroscopy and performed biochemical studies. Our results demonstrated that the reduced YkuV has a low midpoint redox potential, allowing it to reduce a variety of protein substrates. The overall structures of both oxidized and reduced forms are similar, with a typical thioredoxin-like fold. However, significant conformational changes in the Cys-Xaa-Xaa-Cys active motif of the tertiary structures are observed between the two forms. In addition, the backbone dynamics provide further insights in understanding the strong redox potential of the reduced YkuV. Furthermore, we demonstrated that YkuV is able to reduce different protein substrates in vitro. Together, our results clearly established that YkuV may function as a general thiol:disulfide oxidoreductase, which acts as an alternative for thioredoxin or thioredoxin reductase to maintain the reducing environment in the cell cytoplasm.

Mechanistic Implications of the Structure of the Mixed-Disulfide Intermediate of the Disulfide Oxidoreductase, 2-Ketopropyl-Coenzyme M Oxidoreductase/Carboxylase,

The structure of the mixed, enzyme-cofactor disulfide intermediate of ketopropyl-coenzyme M oxidoreductase/carboxylase has been determined by X-ray diffraction methods. Ketopropyl-coenzyme M oxidoreductase/carboxylase belongs to a family of pyridine nucleotide-containing flavin-dependent disulfide oxidoreductases, which couple the transfer of hydride derived from the NADPH to the reduction of protein cysteine disulfide. Ketopropyl-coenzyme M oxidoreductase/carboxylase, a unique member of this enzyme class, catalyzes thioether bond cleavage of the substrate, 2-ketopropyl-coenzyme M, and carboxylation of what is thought to be an enzyme-stabilized enolacetone intermediate. The mixed disulfide of 2-ketopropyl-coenzyme M oxidoreductase/carboxylase was captured through crystallization of the enzyme with the physiological products of the reaction, acetoacetate, coenzyme M, and NADP, and reduction of the crystals with dithiothreitol just prior to data collection. Density in the active-site environment consistent with acetone, the product of reductive decarboxylation of acetoacetate, was revealed in this structure in addition to a well-defined hydrophobic pocket or channel that could be involved in the access for carbon dioxide. The analysis of this structure and that of a coenzyme-M-bound form provides insights into the stabilization of intermediates, substrate carboxylation, and product release.

Insights on a New PDI-like Family: Structural and Functional Analysis of a Protein Disulfide Oxidoreductase from the Bacterium Aquifex aeolicus

A potential role in disulfide bond formation in the intracellular proteins of thermophilic organisms has recently been attributed to a new family of protein disulfide isomerase (PDI)-like proteins. Members of this family are characterized by a molecular mass of about 26kDa and by two Trx folds, each comprising a CXXC active site motif. We report on the functional and structural characterization of a new member of this family, which was isolated from the thermophilic bacterium Aquifex aeolicus (AaPDO). Functional studies have revealed the high catalytic efficiency of this enzyme in reducing, oxidizing and isomerizing disulfide bridges. Site-directed mutagenesis experiments have suggested that its two active sites have similar functional properties, i.e. that each of them imparts partial activity to the enzyme. This similarity was confirmed by the analysis of the enzyme crystal structure, which points to similar geometrical parameters and solvent accessibilities for the two active sites. The results demonstrated that AaPDO is the most PDI-like of all prokaryotic proteins so far known. Thus, further experimental studies on this enzyme are likely to provide important information on the eukaryotic homologue.

Temperature-, SDS-, and pH-Induced Conformational Changes in Protein Disulfide Oxidoreductase from the Archaeon Pyrococcus furiosus: A Dynamic Simulation and Fourier Transform Infrared Spectroscopic Study

The effect of SDS, pD, and temperature on the structure and stability of the protein disulfide oxidoreductase from Pyrococcus furiosus (PfPDO) was investigated by molecular dynamic (MD) simulations and FT-IR spectroscopy. pD affects the thermostability of alpha-helices and beta-sheets differently, and 0.5% or higher SDS concentration influences the structure significantly. The experiments allowed us to detect a secondary structural reorganization at a definite temperature and pD which may correlate with a high ATPase activity of the protein. The MD simulations supported the infrared data and revealed the different behavior of the N and C terminal segments, as well as of the two active sites.

Copper Stress Causes an in Vivo Requirement for the Escherichia coli Disulfide Isomerase DsbC

In Escherichia coli, the periplasmic disulfide oxidoreductase DsbA is thought to be a powerful but nonspecific oxidant, joining cysteines together the moment they enter the periplasm. DsbC, the primary disulfide isomerase, likely resolves incorrect disulfides. Given the reliance of protein function on correct disulfide bonds, it is surprising that no phenotype has been established for null mutations in dsbC. Here we demonstrate that mutations in the entire DsbC disulfide isomerization pathway cause an increased sensitivity to the redox-active metal copper. We find that copper catalyzes periplasmic disulfide bond formation under aerobic conditions and that copper catalyzes the formation of disulfide-bonded oligomers in vitro, which DsbC can resolve. Our data suggest that the copper sensitivity of dsbC- strains arises from the inability of the cell to rearrange copper-catalyzed non-native disulfides in the absence of functional DsbC. Absence of functional DsbA augments the deleterious effects of copper on a dsbC- strain, even though the dsbA- single mutant is unaffected by copper. This may indicate that DsbA successfully competes with copper and forms disulfide bonds more accurately than copper does. These findings lead us to a model in which DsbA may be significantly more accurate in disulfide oxidation than previously thought, and in which the primary role of DsbC may be to rearrange incorrect disulfide bonds that are formed during certain oxidative stresses.

The thiol-disulfide oxidoreductase system in the cold-adapted bacterium Pseudoalteromonas haloplanktis TAC 125: discovery of a novel disulfide oxidoreductase enzyme

In prokaryotes, protein disulfide bond oxidation, reduction and isomerization are catalyzed by members of the thioredoxin superfamily, characterized by the conserved C-X-X-C motif in their active site. Thioredoxins and glutaredoxins contribute to the reducing power in the cytoplasm, while the Dsb system catalyzes disulfide bonds formation in the periplasmic space. This paper addresses the question of disulfide bonds formation in a cold-adapted micro-organism, Pseudoalteromonas haloplanktis TAC 125 (PhTAC125) by characterizing the DsbA system. We found distinctive features respect mesophilic counterparts that highlighted for the first time the occurrence of two adjacent chromosomal DsbA genes organised in a functional operon. The sophisticated transcriptional regulation mechanism that controls the expression of these two genes was also defined. The two DsbA proteins, named PhDsbA and PhDsbA2, respectively, were expressed in Escherichia coli and characterized. Results reported in this paper provide some insights into disulfide bonds formation in a micro organism isolated in the Antarctic sea water.

Requirements for the Different Cysteines in the Chemotactic and Desensitizing Activity of Human Thioredoxin

Thioredoxin (Trx) is a protein disulfide oxidoreductase that can be secreted and act as a chemoattractant for leukocytes. Like chemokines, it causes desensitization of monocytes against its chemotactic activity and that of monocyte chemoattractant protein-1 (MCP-1). To investigate the role of the redox properties of Trx, and particularly of some of its five cysteines, in its chemotactic and desensitizing action, we tested different mutants, including Trx80, a truncated form, and various mutants lacking specific cysteines: Trx C62S/C73S and the redox-inactive mutant Trx C32S/C35S. Of the mutants, only Trx80 maintained the chemotactic activity of wild-type Trx toward both monocytes and polymorphonuclear neutrophils, all of them desensitized monocytes against wild-type Trx or MCP-1, but not chemotactic peptide formyl-methionyl-leucil peptide. These data indicate that different redox-active cysteines are important for Trx chemotactic action, whereas its desensitizing action does not have these requirements, suggesting a redox-independent mechanism.

Reactivities of Quinone-free DsbB from Escherichia coli

DsbB is a disulfide oxidoreductase present in the Escherichia coli plasma membrane. Its cysteine pairs, Cys41-Cys44 and Cys104-Cys130, facing the periplasm, as well as the bound quinone molecules play crucial roles in oxidizing DsbA, the protein dithiol oxidant in the periplasm. In this study, we characterized quinone-free forms of DsbB prepared from mutant cells unable to synthesize ubiquinone and menaquinone. While such preparations lacked detectable quinones, previously reported lauroylsarcosine treatment was ineffective in removing DsbB-associated quinones. Moreover, DsbB-bound quinone was shown to contribute to the redox-dependent fluorescence changes observed with DsbB. Now we reconfirmed that redox potentials of cysteine pairs of quinone-free DsbB are lower than that of DsbA, as far as determined in dithiothreitol redox buffer. Nevertheless, the quinone-free DsbB was able to oxidize approximately 40% of DsbA in a 1:1 stoichiometric reaction, in which hemi-oxidized forms of DsbB having either disulfide are generated. It was suggested that the DsbB-DsbA system is designed in such a way that specific interaction of the two components enables the thiol-disulfide exchanges in the "forward" direction. In addition, a minor fraction of quinone-free DsbB formed the DsbA-DsbB disulfide complex stably. Our results show that the rapid and the slow pathways of DsbA oxidation can proceed up to significant points, after which these reactions must be completed and recycled by quinones under physiological conditions. We discuss the significance of having such multiple reaction pathways for the DsbB-dependent DsbA oxidation.

The Genomics of Disulfide Bonding and Protein Stabilization in Thermophiles

Thermophilic organisms flourish in varied high-temperature environmental niches that are deadly to other organisms. Recently, genomic evidence has implicated a critical role for disulfide bonds in the structural stabilization of intracellular proteins from certain of these organisms, contrary to the conventional view that structural disulfide bonds are exclusively extracellular. Here both computational and structural data are presented to explore the occurrence of disulfide bonds as a protein-stabilization method across many thermophilic prokaryotes. Based on computational studies, disulfide-bond richness is found to be widespread, with thermophiles containing the highest levels. Interestingly, only a distinct subset of thermophiles exhibit this property. A computational search for proteins matching this target phylogenetic profile singles out a specific protein, known as protein disulfide oxidoreductase, as a potential key player in thermophilic intracellular disulfide-bond formation. Finally, biochemical support in the form of a new crystal structure of a thermophilic protein with three disulfide bonds is presented together with a survey of known structures from the literature. Together, the results provide insight into biochemical specialization and the diversity of methods employed by organisms to stabilize their proteins in exotic environments. The findings also motivate continued efforts to sequence genomes from divergent organisms.

Crystal structure of a protein disulfide oxidoreductase fromAquifex aeolicus

Crystal structure of a protein disulfide oxidoreductase from<i>Aquifex aeolicus</i>

Characteristics of Thiol:Protein Disulfide Oxidoreductase from Wheat (Triticum aestivum L.) Grain

Biochemical properties of a homogenous preparation of thiol:protein disulfide oxidoreductase (TPDO, EC 1.8.4.2) isolated for the first time from mature wheat (Triticum aestivum L.) grain were studied. According to polyacrylamide gel electrophoresis data, the molecular weight of TPDO is around 167 kD, the enzyme consisting of two subunits of 77 and 73 kD, which differentiates TPDO from known enzymes of SH/SS-metabolism of wheat caryopses. In substrate specificity and enzymatic characteristics (pH and temperature optima) TPDO is similar to analogous enzymes of animal tissues. Inhibition of disulfide reductase activity by alkylating agents and heavy metal ions suggests the participation of active center SH-groups in the catalytic act and classes the enzyme as a member of the thioredoxin superfamily. The SS-reductase reduces aggregating capacity of acetic acid-soluble fraction of wheat storage proteins. The proposed physiological role of TPDO is participation in creation and regulation of SH/SS-status of wheat endosperm proteins and formation of the rheological properties of gluten.

Stress-dependent regulation of a monothiol glutaredoxin gene fromSchizosaccharomyces pombe

Glutaredoxin (Grx) is a small, heat-stable protein acting as a multi-functional glutathione-dependent disulfide oxidoreductase. In this work, a gene encoding the monothiol glutaredoxin Grx4 was cloned from the genomic DNA of the fission yeast Schizosaccharomyces pombe. The determined DNA sequence carries 1706 bp, which is able to encode the putative 244 amino acid sequence of Grx with 27 099 Da. It does not contain an intron, and the sequence CGFS is found in the active site. Grx activity was increased 1.46-fold in S. pombe cells harboring the cloned Grx4 gene, indicating that the Grx4 gene is in vivo functioning. Although aluminum, cadmium, and hydrogen peroxide marginally enhanced the synthesis of beta-galactosidase from the Grx4-lacZ fusion gene, NO-generating sodium nitroprusside (0.5 mmol/L and 1.0 mmol/L) and potassium chloride (0.2 mol/L and 0.5 mol/L) significantly enhanced it. The Grx4 mRNA level was also enhanced after the treatment with sodium nitroprusside and potassium chloride. The synthesis of beta-galactosidase from the Grx4-lacZ gene was increased by fermentable carbon sources, such as glucose (lower than 2%) and sucrose, but not by nonfermentable carbon sources such as acetate and ethanol. The basal expression of the S. pombe Grx4 gene did not depend on the presence of Pap1. These results imply that the S. pombe monothiol Grx4 gene is genuinely functional and regulated by a variety of stresses.

Identification of an Entamoeba histolytica gene encoding a protein disulfide isomerase that functionally complements the dsbA mutation in Escherichia coli

0 d In vivo, as in vitro, the tertiary structure of a protein is etermined by its amino acid sequence. Despite the ability f some isolated polypeptide to be denatured and refolded n vitro in the absence of other proteins, correct folding and ssembly of polypeptides in vivo involves the assistance of ther proteins, collectively named “foldases” [1]. Protein isulfide isomerase activity (PDI, EC 5.3.4.1), encoded by n eukaryotic family of foldase genes, is a protein-thiol xidoreductase that catalyzes the oxidation, reduction, and somerization of disulfide bonds in nascent polypeptides [2]. n the endoplasmic reticulum compartment, PDI exhibits xidative and reductive activities, while in reducing envionments (such as the cytosol, endosomes or cytoplasmic embrane) behaves just as a reductase [3]. In yeast and ammalian cells, the PDI subcellular localization and funcion suggest that it plays a key roll in the secretory pathway 4]. Structurally, PDI proteins share a region, of about 00 amino acid residues, that is highly homologous to the rokaryotic protein thioredoxin, thus known as “thioredoxinr Tx-domain”. The active site of Tx-domains contains the otif WCGHCK, in which the two cysteine residues cycle Amebiasis is a major cause of death in developing countries. Worldwide, it has been estimated that at least 40,000 people die every year by invasive infection of the etiological agent, the protozoan parasite Entamoeba histolytica [5,6]. In this pathogen the formation of accurate intraor inter-molecular disulfide bonds is an important biochemical step in favor of the correct folding status of proteins, such as the virulence factors amoebapores and Gal/GalNAc-binding lectin [7,8]. We have investigated whether E. histolytica encodes proteins with disulfide oxidoreductase activity, like PDI enzymes, particularly with an active in vivo oxidase activity. Our approach was based on the molecular isolation of actively expressed genes, followed by a functional complementation test. In an initial report, we described the isolation of a cDNA fragment coding for the C-terminal region of a putative EhPDI protein [9]. Here we extend that observation and report the complete characterization of an E. histolytica cDNA sequence encoding a polypeptide with high similarity to the PDI protein family, hence named EhPDI, as well as a phylogenetic inference analysis, and the functional evaluation of its oxidase activity (using an etween the dithiol and disulfide oxidation states [2,4].