Disulfide Catalyst Research Articles

A Secreted Disulfide Catalyst Controls Extracellular Matrix Composition and Function

Disulfide bond formation in secretory proteins occurs primarily in the endoplasmic reticulum (ER), where multiple enzyme families catalyze cysteine cross-linking. Quiescin sulfhydryl oxidase 1 (QSOX1) is an atypical disulfide catalyst, localized to the Golgi apparatus or secreted from cells. We examined the physiological function for extracellular catalysis of de novo disulfide bond formation by QSOX1. QSOX1 activity was required for incorporation of laminin into the extracellular matrix (ECM) synthesized by fibroblasts, and ECM produced without QSOX1 was defective in supporting cell-matrix adhesion. We developed an inhibitory monoclonal antibody against QSOX1 that could modulate ECM properties and undermine cell migration.

Tungsten disulfide catalysts from tetraalkylammonium thiotungstates by ex situ activation, their properties and HDS activity

The role of carbon coming from tetraalkylammonium thiotungstate precursors during the ex situ activation of WS2 catalysts was herein studied through the comparison of two different thiosalts, ammonium tetrathiotungstate (ATT, without carbon) and cetyltrimethylammonium tetrathiotungstate (CTATT, with carbon). The influence on the resulting WS2 catalysts, of a N2 vs a H2S/H2 (20% H2S) atmosphere during ex situ activation was also evaluated. Freshly obtained catalysts were characterized by N2 adsorption–desorption isotherms, X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX), while their catalytic properties were evaluated in the hydrodesulfurization of dibenzothiophene at 3.1MPa and 623K. No significant difference was found in the textural and morphological properties of the final WS2 catalysts derived from thermal decomposition of ATT under N2 flow, compared to 20% H2S/H2 flow. In contrast, the textural, morphological and catalytic properties of WS2 catalysts derived from CTATT were strongly influenced by the nature of the atmosphere. Samples of WS2 derived from ATT showed an absence of porosity, while WS2 catalysts formed from CTATT presented a mesoporous organization characterized by type IV N2 isotherms. XRD and TEM showed that the use of CTATT induces a strong destacking of the WS2 particles and the excessive formation of amorphous carbon, thus yielding less active WS2 catalysts which confirm the negative role of carbon-containing tetraalkylammonium precursors in the activation of WS2 catalysts, as opposed to their positive influence in the activation of MoS2 catalysts. The very high activity of the WS2 catalyst obtained from ATT is attributed to an optimized incorporation of structural carbon inside the WS2 structure. Finally, selectivity results show the depleted hydrogenating character of the WS2 catalysts formed from CTATT.

Wet Chemical Synthesis of Nanostructured Molybdenum Disulfide Catalysts for Electrochemical Hydrogen Production

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Structure of a Baculovirus Sulfhydryl Oxidase, a Highly Divergent Member of the Erv Flavoenzyme Family

Genomes of nucleocytoplasmic large DNA viruses (NCLDVs) encode enzymes that catalyze the formation of disulfide bonds between cysteine amino acid residues in proteins, a function essential for the proper assembly and propagation of NCLDV virions. Recently, a catalyst of disulfide formation was identified in baculoviruses, a group of large double-stranded DNA viruses considered phylogenetically distinct from NCLDVs. The NCLDV and baculovirus disulfide catalysts are flavin adenine dinucleotide (FAD)-binding sulfhydryl oxidases related to the cellular Erv enzyme family, but the baculovirus enzyme, the product of the Ac92 gene in Autographa californica multiple nucleopolyhedrovirus (AcMNPV), is highly divergent at the amino acid sequence level. The crystal structure of the Ac92 protein presented here shows a configuration of the active-site cysteine residues and bound cofactor similar to that observed in other Erv sulfhydryl oxidases. However, Ac92 has a complex quaternary structural arrangement not previously seen in cellular or viral enzymes of this family. This novel assembly comprises a dimer of pseudodimers with a striking 40-degree kink in the interface helix between subunits. The diversification of the Erv sulfhydryl oxidase enzymes in large double-stranded DNA viruses exemplifies the extreme degree to which these viruses can push the boundaries of protein family folds.

HDS of DBT with Molybdenum Disulfide Catalysts Prepared by In Situ Decomposition of Alkyltrimethylammonium Thiomolybdates

Three alkyltrimethylammonium thiomolybdates, [R–N(CH3)3]2MoS4 (where R = lauryl, myristyl or cetyl) were synthesized in aqueous solution, and characterized by 1H-NMR spectroscopy. These alkyltrimethylammonium thiomolybdates were used (the lauryl and myristyl thiomolybdates for the first time) as precursors for in situ prepared MoS2 catalysts, activated during the hydrodesulfurization of dibenzothiophene. The catalysts were analyzed by EDX, showing large voids and a S/Mo ratio around 2. High surface areas up to 443 m2/g and type IV adsorption–desorption nitrogen isotherms were obtained. X-ray diffraction showed that the catalysts are poorly crystalline, with a very weak (002) peak intensity for all samples except the MoS2 catalyst prepared from pure ammonium tetrathiomolybdate precursor. A high dibenzothiophene conversion (74%) was observed with the catalyst obtained from the lauryltrimethylammonium thiomolybdate precursor, attributed mainly to its high specific surface area. Selectivity results showed that all the prepared catalysts strongly favored the hydrogenation pathway.

Dimer Interface Migration in a Viral Sulfhydryl Oxidase

Large double-stranded DNA viruses, including poxviruses and mimiviruses, encode enzymes to catalyze the formation of disulfide bonds in viral proteins produced in the cell cytosol, an atypical location for oxidative protein folding. These viral disulfide catalysts belong to a family of sulfhydryl oxidases that are dimers of a small five-helix fold containing a Cys-X-X-Cys motif juxtaposed to a flavin adenine dinucleotide cofactor. We report that the sulfhydryl oxidase pB119L from African swine fever virus (ASFV) uses for self-assembly surface different from that observed in homologs from mammals, plants, and fungi. Within a protein family, different packing interfaces for the same oligomerization state are extremely rare. We find that the alternate dimerization mode seen in ASFV pB119L is not characteristic of all viral sulfhydryl oxidases, as the flavin-binding domain from a mimivirus sulfhydryl oxidase assumes the same dimer structure as the known eukaryotic enzymes. ASFV pB119L demonstrates the potential of large double-stranded DNA viruses, which have faster mutation rates than their hosts and the tendency to incorporate host genes, to pioneer new protein folds and self-assembly modes.

Properties of the Thioredoxin Fold Superfamily Are Modulated by a Single Amino Acid Residue

The ubiquitous thioredoxin fold proteins catalyze oxidation, reduction, or disulfide exchange reactions depending on their redox properties. They also play vital roles in protein folding, redox control, and disease. Here, we have shown that a single residue strongly modifies both the redox properties of thioredoxin fold proteins and their ability to interact with substrates. This residue is adjacent in three-dimensional space to the characteristic CXXC active site motif of thioredoxin fold proteins but distant in sequence. This residue is just N-terminal to the conservative cis-proline. It is isoleucine 75 in the case of thioredoxin. Our findings support the conclusion that a very small percentage of the amino acid residues of thioredoxin-related proteins are capable of dictating the functions of these proteins.

Cyclohexene hydrogenation with molybdenum disulfide catalysts prepared by ex situ decomposition of ammonium thiomolybdate-cetyltrimethylammonium thiomolybdate mixtures

Ammonium tetrathiomolybdate (ATTM) is treated with cetyltrimethylammonium chloride (CTAC) using several ATTM/CTAC ratios. Reaction of ATTM with the limiting reagent CTAC gives the carbon-containing compound cetyltrimethylammonium tetrathio-molybdate (CTAT), resulting in different ATTM–CTAT mixtures or precursors which are then decomposed in N 2 at 723 K, yielding mesoporous samples with surface areas of over 260 m 2/g. Analysis by XRD and electron microscopy correspond to a well dispersed MoS 2–2H phase. The activity of the catalysts is tested in a batch reactor for cyclohexene hydrogenation, where those prepared from ATTM–CTAT precursors are up to seven times more active than the catalyst obtained by thermal decomposition of pure ATTM. The enhanced catalytic activity of these catalysts is attributed to a sulfide phase containing structural carbon.

Synthesis, characterization and cyclohexene hydrogenation activity of high surface area molybdenum disulfide catalysts

An ammonium tetrathiomolybdate (ATTM) catalyst precursor is synthesized and then thermally decomposed at different temperatures in N2 or H2 atmosphere. Characterization of the resulting compounds by powder X-ray diffraction (XRD) and surface area analysis indicates the formation of MoS2–2H with a surface area of 5–9 m2/g. When ATTM is treated with cetyltrimethylammonium chloride and then decomposed in N2 at 723 K, the resulting material has a surface area nearing 200 m2/g. If treatment also includes hydrazine, the surface area of the resulting MoS2–2H reaches 215 m2/g. Analysis by XRD and electron microscopy shows a noticeable dispersion in the layers of the resulting MoS2. The catalytic activity of the materials is tested in a batch reactor for cyclohexene hydrogenation, where the highest activity sulfides are those obtained by thermal decomposition of the chemically treated precursors in N2.

XPS study of molybdenum sulfide catalyst exposed to CO and H 2

Amorphous MoS 3 (air-dried precipitate), crystalline MoS 2 (made in the laboratory under nitrogenous atmosphere), and commercial molybdenum disulfide catalysts have been investigated by X-ray photoelectron spectroscopy (XPS). The chemical species present on the surface and the S/Mo atomic ratios of laboratory catalysts were compared to those present on a commercial molybdenum disulfide catalyst before and after treatment with CO and H 2. Pretreatment of MoS 2 with CO followed by H 2 showed that CO was adsorbed on the surface with no change in the chemical oxidation state of Mo and S. However, the results indicated that CO was not adsorbed when the sequence of gas exposures was reversed.

Study of γ-Alumina-Supported Hydrotreating Catalyst: I. Adsorption of Bare MoS2Sheets on γ-Alumina Surfaces

We herein report on the PW-DFT study of molybdenum disulfide catalyst supported on γ-alumina. An Mo4S8 sheet, in a complete periodical environment, was docked to three surfaces of alumina. We found that the alumina surface controlled the orientation and the morphology of MoS2 sheets. The results show that for all alumina surfaces the Mo-edge- and Mo−S-edge-adsorbed MoS2 sheets are the most stable configurations.

Characterization and HDS Activity of Mesoporous MoS2 Catalysts Prepared by in Situ Activation of Tetraalkylammonium Thiomolybdates

Unsupported molybdenum disulfide catalysts with unique morphological pore structure were synthesized from tetraalkylammonium thiometalates precursors by in situ activation during the hydrodesulfurization (HDS) of dibenzothiophene. The precursors used in this study are ammonium thiomolybdate (ATM), tetrapropylammonium thiomolybdate, tetrapentylammonium thiomolybdate, tetrahexylammonium thiomolybdate, tetraheptylammonium thiomolybdate (THepATM), and tetraoctylammonium thiomolybdate. The thermogravimetrical analysis carried out under nitrogen demonstrated that all precursors yield MoS2 bulk structure at 623 K, after one or two decomposition steps. The morphology of these catalysts observed by scanning electron microscopy presents large hemispherical or ovoid cavities with a cheese-like porous arrangement, high surface area (from 255 up to 329 m2/g), high content of carbon (C/Mo=2.7–4.0), and type IV adsorption–desorption isotherms of nitrogen. The nature of the alkyl group affects the surface area, the pore size distribution, and the HDS selectivity. The highest selectivity for direct C–S bond cleavage is observed for the molybdenum disulfide catalyst formed from THepATM. X-ray diffraction studies showed that the catalysts are poorly crystallized, with a very weak intensity of the (002) line of 2H-MoS2 characteristic of exfoliated samples.

Identification of the Ubiquinone-binding Domain in the Disulfide Catalyst Disulfide Bond Protein B

Disulfide bond (Dsb) formation is catalyzed in the periplasm of prokaryotes by the Dsb proteins. DsbB, a key enzyme in this process, generates disulfides de novo by using the oxidizing power of quinones. To explore the mechanism of this newly described enzymatic activity, we decided to study the ubiquinone-protein interaction and identify the ubiquinone-binding domain in DsbB by cross-linking to photoactivatable quinone analogues. When purified Escherichia coli DsbB was incubated with an azidoubiquinone derivative, 3-azido-2-methyl-5-[(3)H]methoxy-6-decyl-1,4-benzoquinone ([(3)H]azido-Q), and illuminated with long wavelength UV light, the decrease in enzymatic activity correlated with the amount of 3-azido-2-methyl-5-methoxy-6-decyl-1,4-benzoquinone (azido-Q) incorporated into the protein. One azido-Q-linked peptide with a retention time of 33.5 min was obtained by high performance liquid chromatography of the V8 digest of [(3)H]azido-Q-labeled DsbB. This peptide has a partial NH(2)-terminal amino acid sequence of NH(2)-HTMLQLY corresponding to residues 91-97. This sequence occurs in the second periplasmic domain of the inner membrane protein DsbB in a loop connecting transmembrane helices 3 and 4. We propose that the quinone-binding site is within or very near to this sequence.

Modelling hydrogen transport in molybdenum disulfide catalysts with muon spin relaxation spectroscopy

Muon spin relaxation (µSR) spectra of a molybdenum disulfide and cobalt-promoted molybdenum disulfide catalyst were measured. The aim was to use the positive muon (µ) to model the binding and transport of hydrogen-like species in the catalyst. Muon implantation bypasses the first function of the catalyst, to dissociate molecular hydrogen. We observed classical diffusion at temperatures above 150 K which is easily described by the Arrhenius law. At lower temperatures (T < 100 K) we observed multi-phonon assisted quantum diffusion. The addition of cobalt to molybdenum disulfide decreased the activation energy for the diffusion of hydrogen-like particles, an effect which may account, at least in part, for the promotional role of cobalt in MoS2-based hydrodesulfurization catalysts. Copyright © 2000 John Wiley & Sons, Ltd.

Interaction of thiophene with a molybdenum disulfide catalyst—an inelastic neutron scattering study

The inelastic neutron scattering (INS) spectra of thiophene adsorbed on alumina, MoS2/alumina and CoMoS2/alumina catalysts reduced in hydrogen were obtained for surface concentrations of one thiophene monolayer or less. A series of model complexes was also investigated: [Cr(CO)3(η5-thiophene)], [Mn(CO)3(η5-thiophene)][CF3SO3], [Fe(η5-C5H5)(CO)2(η1-S-thiophene)][BF4] and [Fe(η5-C5H5) (CO)2]2. The spectra of adsorbed thiophene were obtained by subtraction of the spectra of the bare catalysts. Adsorbed thiophene was identified on the alumina support. The mass of thiophene adsorbed on the catalysts increased with increasing molybdenum content in the catalyst and most significantly with cobalt. Adsorbed thiophene interacts weakly with the surface; it is more like pure thiophene than co-ordinated thiophene. It lies mostly with the molecule aligned parallel with the surface with possibly a small proportion (5–10%) upright (S-bound). We discuss how these results help us to understand the role of the catalyst in thiophene hydrodesulfurisation.

Preparation of MoS2 and WS2 catalysts by in situ decomposition of ammonium thiosalts

The in situ decomposition of ammonium thiometallates during the hydrodesulfurization (HDS) of dibenzothiophene (DBT), to obtain molybdenum disulfide and tungsten disulfide catalysts, was investigated. It was found that very efficient catalysts for the HDS of DBT were obtained by in situ decomposition. Mechanical uniaxial pressing of the precursors (ammonium thiometallates) affected both textural and catalytic properties of the catalysts. Surface areas of molybdenum and tungsten disulfides increased as a function of uniaxial pressing, while catalytic activities went through a maximum. For MoS2, the hydrogenation selectivity was much higher for in situ catalysts than for ex situ ones. For WS2 catalysts, the hydrogenation selectivity was less sensitive to the condition of decomposition (ex situ/in situ). The surface S/M (M = Mo, W) atomic ratio from the Auger signal decreased as a function of uniaxial pressing, while the C/M ratio remained almost constant at 1.6. The best catalyst showed an experimental S/Mo ratio that is slightly higher than the stoichiometric value. The effect of in situ decomposition and mechanical deformation of thiometallate precursors is discussed.

5] Disulfide bond catalysts in Escherichia coli

Publisher Summary The chapter describes general methods for rapidly blocking thiol-disulfide exchange and for analyzing cell extracts in ways allowing for the distinction among the oxidized and reduced forms of proteins. A sample labeling protocol specifically designed to detect defects in disulfide bond formation in Escherichia coli ( E. coli) is detailed as one specific example; however, modifications of this protocol should work with many species. In addition, the trapping and separation techniques described have many applications for the study of disulfide catalysis using purified proteins in vitro , and for the study of the folding process itself, in the absence of catalysts. These applications, additional methods, and the theory used to study disulfide exchange have been described in detail. The chapter also describes a generally applicable method to determine the equilibrium redox properties of disulfide catalysts. E. coli mutants that are deficient in thioredoxin reductase and in the disulfide bond catalysts DsbA, B, C, and D show altered abilities in disulfide bond formation in vivo , demonstrating the important role of these folding catalysts in the cell. One advantage of studying these catalysts is that disulfide exchange, both in vitro and in the cell, can be frozen at any instant in time using thiol-trapping agents and the reaction intermediates present within the substrate proteins and catalysts separated and quantified. This provides a unique opportunity to study the kinetics of folding catalysis in vitro and in vivo .

Kinetics of reverse water gas shift (RWGS) reaction on metal disulfide catalysts

The hydrogenation of CO 2 was studied on disulfides of molybdenum and tungsten by comparison with that on the group VIII metals of Fe, Co, and Ni supported on Al 2O 3. The hydrogenation activity was lower on the disulfides on a per active site of catalyst basis than on the transition metals, however, the selective reverse water gas shift (RWGS) reaction (CO 2 + H 2 → CO + H 2O) was observed on the disulfides. The selectivity was close to ca. 100% in the reaction conditions examined. The rate was expressed by the equation: r = kP 0.61–0.73 CO 2 P 0.36 H 2 on the disulfides, and the activation energy was ca. 18.0–19.1 kcal mol −1. The disulfides exhibited little activities for the hydrogenation of CO (viz. CO + 3H 2 → CH4 + H 2O) and also for the disproportionation of CO (viz. 2CO → C + CO 2). These results were in contrast to those for the transition metals where high activities were observed for both reactions, suggesting that the retardation of CO bond cleavage in the CO molecule produced by the CO 2 hydrogenation must be the cause for the selective hydrogenation of CO 2 to CO on the disulfides. The effect of supports on the hydrogenation of CO 2 was also investigated for MoS 2. The reaction rate on a per active site of catalyst basis was not influenced by the supports, suggesting that the CO 2H 2 reaction is insensitive to the morphology of MoS 2 supported on metal oxides.

Structural analysis of three His32 mutants of DsbA: support for an electrostatic role of His32 in DsbA stability.

DsbA, a 21-kDa protein from Escherichia coli, is a potent oxidizing disulfide catalyst required for disulfide bond formation in secreted proteins. The active site of DsbA is similar to that of mammalian protein disulfide isomerases, and includes a reversible disulfide bond formed from cysteines separated by two residues (Cys30-Pro31-His32-Cys33). Unlike most protein disulfides, the active-site disulfide of DsbA is highly reactive and the oxidized form of DsbA is much less stable than the reduced form at physiological pH. His32, one of the two residues between the active-site cysteines, is critical to the oxidizing power of DsbA and to the relative instability of the protein in the oxidized form. Mutation of this single residue to tyrosine, serine, or leucine results in a significant increase in stability (of approximately 5-7 kcal/mol) of the oxidized His32 variants relative to the oxidized wild-type protein. Despite the dramatic changes in stability, the structures of all three oxidized DsbA His32 variants are very similar to the wild-type oxidized structure, including conservation of solvent atoms near the active-site residue, Cys30. These results show that the His32 residue does not exert a conformational effect on the structure of DsbA. The destabilizing effect of His32 on oxidized DsbA is therefore most likely electrostatic in nature.

Catalyst performance of MoS 2 and WS 2 for the CO 2-reforming of CH 4 Suppression of carbon deposition

The catalyst performance of MoS 2 and WS 2 was verified for the CO 2-reforming of CH 4 through the comparison with that of Ni SiO 2 . No catalyst deactivation was observed on the disulfides, although the rate was much smaller than that on Ni. It was found that the disulfides exhibited a poor ability for the direct decomposition of CH 4. The poor ability did not lead to carbon deposition during reforming reaction, which assured a stable activity. It was also observed that the rate equation was completely different between disulfide catalysts and Ni catalyst. The reaction order was positive with respect to the CH 4 partial pressure and negative with respect to the CO 2 partial pressure on the former catalysts, while negative with respect to CH 4 partial pressure and positive with respect to the CO 2 partial pressure on the latter. The observed reaction kinetics suggested that the surface of the disulfide catalyst was abundant in adsorbed CO 2, while the surface of Ni catalyst was abundant in adsorbed CH 4. The abundance in adsorbed CO 2 was considered an unfavorable condition for the direct decomposition of CH 4 and as a result, carbon deposition was suppressed during CO 2-reforming on disulfide catalyst. Sulfur tolerance was found to be an additional performance of the disulfide catalyst.