Showing papers by "Isabel Moura published in 2014"
TL;DR: EPR, resonance Raman, and MCD spectroscopies have been used to determine the redox states of N2OR's tetranuclear copper active site, showing that only fully reduced Cu(Z)* is catalytically competent in rapid turnover with N2O.
Abstract: N2OR has been found to have two structural forms of its tetranuclear copper active site, the 4CuS CuZ* form and the 4Cu2S CuZ form EPR, resonance Raman, and MCD spectroscopies have been used to determine the redox states of these sites under different reductant conditions, showing that the CuZ* site accesses the 1-hole and fully reduced redox states, while the CuZ site accesses the 2-hole and 1-hole redox states Single-turnover reactions of N2OR for CuZ and CuZ* poised in these redox states and steady-state turnover assays with different proportions of CuZ and CuZ* show that only fully reduced CuZ* is catalytically competent in rapid turnover with N2O
43 citations
TL;DR: This work reports, for the first time, steady-state kinetics with the Pseudomonas nautica NOR, either in the presence of its physiological electron donor (cyt. c552) or immobilised on a graphite electrode surface, in the absence of its known substrates, namely NO or O2.
23 citations
TL;DR: The 1H–15N heteronuclear single quantum coherence spectra of the reconstituted ORP obtained by strategy 2, in contrast to strategy 1, exhibited large changes, which required sequential assignment in order to identify, by chemical shift differences, the residues affected by the incorporation of the cluster, which is stabilized inside the protein by both electrostatic and hydrophobic interactions.
Abstract: The orange protein (ORP) isolated from the sulfate-reducing bacterium Desulfovibrio gigas (11.8 kDa) contains a mixed-metal sulfide cluster of the type [S2MoS2CuS2MoS2]3- noncovalently bound to the polypeptide chain. The D. gigas ORP was heterologously produced in Escherichia coli in the apo form. Different strategies were used to reconstitute the metal cluster into apo-ORP and obtain insights into the metal cluster synthesis: (1) incorporation of a synthesized inorganic analogue of the native metal cluster and (2) the in situ synthesis of the metal cluster on the addition to apo-ORP of copper chloride and tetrathiomolybdate or tetrathiotungstate. This latter procedure was successful, and the visible spectrum of the Mo–Cu reconstituted ORP is identical to the one reported for the native protein with absorption maxima at 340 and 480 nm. The 1H–15N heteronuclear single quantum coherence spectra of the reconstituted ORP obtained by strategy 2, in contrast to strategy 1, exhibited large changes, which required sequential assignment in order to identify, by chemical shift differences, the residues affected by the incorporation of the cluster, which is stabilized inside the protein by both electrostatic and hydrophobic interactions.
22 citations
TL;DR: DFT calculations confirmed the spin density delocalization over the four sulfur atoms and copper atom, suggesting that 1(red) has a "thiyl radical character", and time dependent DFT calculations identified such ligand to ligand charge transfer transitions.
Abstract: The complex [Ph4P]2[Cu(bdt)2] (1red) was synthesized by the reaction of [Ph4P]2[S2MoS2CuCl] with H2bdt (bdt = benzene-1,2-dithiolate) in basic medium. 1red is highly susceptible toward dioxygen, affording the one electron oxidized diamagnetic compound [Ph4P][Cu(bdt)2] (1ox). The interconversion between these two oxidation states can be switched by addition of O2 or base (Et4NOH = tetraethylammonium hydroxide), as demonstrated by cyclic voltammetry and UV–visible and EPR spectroscopies. Thiomolybdates, in free or complex forms with copper ions, play an important role in the stability of 1red during its synthesis, since in its absence, 1ox is isolated. Both 1red and 1ox were structurally characterized by X-ray crystallography. EPR experiments showed that 1red is a Cu(II)–sulfur complex and revealed strong covalency on the copper–sulfur bonds. DFT calculations confirmed the spin density delocalization over the four sulfur atoms (76%) and copper (24%) atom, suggesting that 1red has a “thiyl radical character”...
18 citations
TL;DR: Resistance assays in E. coli transformed with plasmids containing either of the two recombinant arsenate reductases showed that only DaG20_ArsC3 is functional and able to confer arsenate resistance, and indicates that potassium binding is not essential to have low Km, for Trx-arsenate reduCTases.
Abstract: Desulfovibrio alaskensis G20, a sulfate-reducing bacterium, contains an arsRBC2C3 operon that encodes two putative arsenate reductases, DaG20_ArsC2 and DaG20_ArsC3. In this study, resistance assays in E. coli transformed with plasmids containing either of the two recombinant arsenate reductases, showed that only DaG20_ArsC3 is functional and able to confer arsenate resistance. Kinetic studies revealed that this enzyme uses thioredoxin as electron donor and therefore belongs to Staphylococcus aureus plasmid pI258 and Bacillus subtilis thioredoxin-coupled arsenate reductases family. Both enzymes from this family contain a potassium-binding site, but only in Sa_ArsC does potassium actually binds resulting in a lower K m. Important differences between the S. aureus and B. subtilis enzymes and DaG20_ArsC3 are observed. DaG20_ArsC3 contains only two (Asn10, Ser33) of the four (Asn10, Ser33, Thr63, Asp65) conserved amino acid residues that form the potassium-binding site and the kinetics is not significantly affected by the presence of either potassium or sulfate ions. Isothermal titration calorimetry measurements confirmed nonspecific binding of K(+) and Na(+), corroborating the non-relevance of these cations for catalysis. Furthermore, the low K m and high k cat values determined for DaG20_ArsC3 revealed that this enzyme is the most catalytically efficient potassium-independent arsenate reductase described so far and, for the first time indicates that potassium binding is not essential to have low K m, for Trx-arsenate reductases.
6 citations
TL;DR: The fluorine-19 chemical shift is an advantageous NMR structural probe in alternative to 1H-NMR [B.Maiti et al. as mentioned in this paper, 2012].
3 citations