RESUMO
The methyltransferase FliB posttranslationally modifies surface-exposed É-N-lysine residues of flagellin, the protomer of the flagellar filament in Salmonella enterica (S. enterica). Flagellin methylation, reported originally in 1959, was recently shown to enhance host cell adhesion and invasion by increasing the flagellar hydrophobicity. The role of FliB in this process, however, remained enigmatic. In this study, we investigated the properties and mechanisms of FliB from S. enterica in vivo and in vitro. We show that FliB is an S-adenosylmethionine (SAM) dependent methyltransferase, forming a membrane associated oligomer that modifies flagellin in the bacterial cytosol. Using X-band electron paramagnetic resonance (EPR) spectroscopy, zero-field 57Fe Mössbauer spectroscopy, methylation assays and chromatography coupled mass spectrometry (MS) analysis, we further found that FliB contains an oxygen sensitive [4Fe-4S] cluster that is essential for the methyl transfer reaction and might mediate a radical mechanism. Our data indicate that the [4Fe-4S] cluster is coordinated by a cysteine rich motif in FliB that is highly conserved among multiple genera of the Enterobacteriaceae family.
Assuntos
Proteínas de Bactérias/metabolismo , Flagelina/metabolismo , Proteínas Ferro-Enxofre/metabolismo , Lisina/metabolismo , Metiltransferases/metabolismo , S-Adenosilmetionina/metabolismo , Salmonella typhi/enzimologia , Proteínas de Bactérias/genética , Flagelina/química , Proteínas Ferro-Enxofre/genética , Lisina/química , Metilação , Metiltransferases/genéticaRESUMO
A redox-switchable self-assembled ZnII 4 L6 cage was synthesized that contains naphthalenediimide (NDI) motifs. Its reduction lent these NDI panels persistent radical anion character. The redox activity of this cage allows it to act as a catalyst for the oxidative coupling of different tetraaryl borates to give biaryls. The catalytic activity of the cage was enhanced following its binding of C60 , which implies a mechanism that does not involve encapsulation of the substrate.
RESUMO
The crystalline phase ß-[N(CH3 )4 ]2 HP3 O9 undergoes a reversible phase transition to γ-[N(CH3 )4 ]2 HP3 O9 , which was studied by dynamic scanning calorimetry and X-ray diffraction. The rotational dynamics of the anion [P3 O9 ]3- were evident from variable temperature 31 P magic angle spinning (MAS) NMR spectroscopy. The rotational dynamics could be simulated with a 3-site jump model, which yields spectra in good agreement with experiment. An activation energy of 0.6â eV could be estimated from line shape analysis. Impedance spectra reflect a bulk proton conductivity of γ-[N(CH3 )4 ]2 HP3 O9 of 6.9×10-5 â S cm-1 at 240 °C and an activation energy of approximately 1.0â eV. Thus this salt features bulk protonic motion, while local rotational anionic motion happens with activation energies of the same order, as suggested by the paddle-wheel mechanism.
RESUMO
We report the formation of a stable neutral diboron diradical simply by coordination of an aromatic dinitrogen compound to an ortho-phenyldiborane. This process is reversible upon addition of pyridine. The diradical species is stable above 200 °C. Computations are consistent with an open-shell triplet diradical with a very small open-shell singlet-triplet energy gap that is indicative of the electronic disjointness of the two radical sites. This opens a new way of generating stable radicals with fascinating electronic properties useful for a large variety of applications.
RESUMO
We have synthesized NOUF6 by direct reaction of NO with UF6 in anhydrous HF (aHF). Based on the unit cell volume and powder diffraction data, the compound was previously reported to be isotypic to O2 PtF6 , however, detailed structural data, such as the atom positions and all information that can be derived from those, were unavailable. We have therefore investigated the compound by using single-crystal and powder X-ray diffraction, IR, Raman, NMR, EPR, and photoluminescence spectroscopy, magnetic measurements, as well as chemical analysis, density determination, and quantum chemical calculations.
RESUMO
A first systematic study upon the preparation and exploration of a series of iron 10-thiacorroles with simple halogenido (F, Cl, Br, I), pseudo-halogenido (N3 , I3 ) and solvent-derived axial ligands (DMSO, pyridine) is reported. The compounds were prepared from the free-base octaethyl-10-thiacorrole by iron insertion and subsequent ligand-exchange reactions. The small N4 cavity of the ring-contracted porphyrinoid results in an intermediate spin (i.s., S=3/2) state as the ground state for the iron(III) ion. In most of the investigated cases, the i.s. state is found unperturbed and independent of temperature, as determined by a combination of X-ray crystallography and magnetometry with (1) Hâ NMR-, EPR-, and Mössbauer spectroscopy. Two exceptions were found. The fluorido iron(III) complex is inhomogenous in the solid and contains a thermal i.s. (S=3/2)âhigh spin (h.s., S=5/2) crossover fraction. On the other side, the cationic bis(pyridine) complex resides in the expected low spin (l.s., S=1/2) state. Chemically, the iron 10-thiacorroles differ from the iron porphyrins mainly by weaker axial ligand binding and by a cathodic shift of the redox potentials. These features make the 10-thiacorroles interesting ligands for future research on biomimetic catalysts and model systems for unusual heme protein active sites.
Assuntos
Compostos Férricos/química , Hemeproteínas/química , Ferro/química , Metaloporfirinas/química , Biomimética , Cristalografia por Raios X , Espectroscopia de Ressonância de Spin Eletrônica , Ligantes , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Estrutura Molecular , Porfirinas/químicaRESUMO
Subtilosin A is a 35-residue, ribosomally synthesized bacteriocin encoded by the sbo-alb operon of Bacillus subtilis. It is composed of a head-to-tail circular peptide backbone that is additionally restrained by three unusual thioether bonds between three cysteines and the α-carbon of one threonine and two phenylalanines, respectively. In this study, we demonstrate that these bonds are synthesized by the radical S-adenosylmethionine enzyme AlbA, which is encoded by the sbo-alb operon and comprises two [4Fe-4S] clusters. One [4Fe-4S] cluster is coordinated by the prototypical CXXXCXXC motif and is responsible for the observed S-adenosylmethionine cleavage reaction, whereas the second [4Fe-4S] cluster is required for the generation of all three thioether linkages. On the basis of the obtained results, we propose a new radical mechanism for thioether bond formation. In addition, we show that AlbA-directed substrate transformation is leader-peptide dependent, suggesting that thioether bond formation is the first step during subtilosin A maturation.
Assuntos
Bacillus subtilis/genética , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Bacteriocinas/metabolismo , Proteínas Ferro-Enxofre/química , Proteínas Ferro-Enxofre/metabolismo , Peptídeos Cíclicos/metabolismo , Sulfetos/química , Motivos de Aminoácidos , Sequência de Aminoácidos , Bacillus subtilis/metabolismo , Proteínas de Bactérias/genética , Bacteriocinas/química , Sequência de Bases , Sítios de Ligação , Cisteína/química , Espectroscopia de Ressonância de Spin Eletrônica , Proteínas Ferro-Enxofre/genética , Dados de Sequência Molecular , Mutagênese , Óperon , Peptídeos Cíclicos/química , Fenilalanina/química , S-Adenosilmetionina/metabolismo , Treonina/químicaRESUMO
The sporulation killing factor (SKF) is a 26-residue ribosomally assembled and posttranslationally modified sactipeptide. It is produced by Bacillus subtilis 168 and plays a key role in its sporulation. Like all sactipeptides, SKF contains a thioether bond, which links the cysteine residue Cys4 with the α-carbon of the methionine residue Met12. In this study we demonstrate that this bond is generated by the two [4Fe-4S] clusters containing radical SAM enzyme SkfB, which is encoded in the skf operon. By mutational analysis of both cluster-binding sites, we were able to postulate a mechanism for thioether generation which is in agreement with that of AlbA. Furthermore, we were able to show that thioether bond formation is specific toward hydrophobic amino acids at the acceptor site. Additionally we demonstrate that generation of the thioether linkage is leader-peptide-dependent, suggesting that this reaction is the first step in SKF maturation.
Assuntos
Proteínas de Bactérias/metabolismo , Proteínas Ferro-Enxofre/metabolismo , Sulfetos/metabolismo , Proteínas de Bactérias/química , Biocatálise , Proteínas Ferro-Enxofre/química , Conformação Molecular , Sulfetos/químicaRESUMO
Soluble alkyl and aryl imido phthalocyanines [Pc(#)Mo(NR)Cl] (R = tBu, Mes) with molybdenum(V) as central metal were prepared and studied by UV-vis and electron paramagnetic resonance (EPR) spectroscopy. As structural analogue to the weakly aggregating, soluble alkyl substituted Pc(#) ligand, a new, more electron deficient octaazaphthalocyanine, the pyrazinoporphyrazine ligand Ppz(#), was designed. The respective alkyl and aryl imido complexes [Ppz(#)Mo(NR)Cl] are the first examples of molybdenum pyrazinoporphyrazines. UV-vis and EPR spectra revealed unexpected differences between the alkyl and the aryl imido complexes, indicating different electronic structures depending on the nature of the axial ligand. The octahedral coordination of the molybdenum atoms by the axial NR and Cl ligands and the equatorial macrocycles could be verified by EPR spectroscopy. This result was also confirmed by the crystal structure of [Pc(#)Mo(NMes)Cl], which crystallizes from CH2Cl2 in the cubic space group Im3.
RESUMO
The synthesis of new tetradentate dianionic N2O2 ligand juglophen (H2jp, 1) and its nickel(II) complex [Ni(jp)] (2) is reported. The unprecedented ligand synthesis is accomplished via oxidative coupling of 1,5-dihydroxynapthalene and o-phenylenediamine by hypervalent phenyliodine(III)-diacetate. Ligand 1 and complex 2 were characterized via NMR, IR, UV-Vis spectroscopy, mass spectrometry, cyclic voltammetry and by XRD analysis. In order to investigate the non-innocent character of ligand 1, [Ni(jp)] (2) was oxidized using AgPF6 to form [Ni(jp)]+ [PF6]- (3) whereas one-electron reduction with [Cp2Co] generated [Cp2Co]+[Ni(jp)]- (4). The paramagnetic nature of the oxidized and reduced species 3 and 4 was validated via EPR spectroscopy and further investigated pursuing DFT calculations at the PBE-D3(BJ)/def2-TZVPP level of theory. Predominantly ligand-centered SOMOs of 3 and 4 are allowing insight towards a deeper understanding of the redox behavior of [Ni(jp)] (2).
RESUMO
Frataxin homologues are important iron chaperones in eukarya and prokarya. Using a native proteomics approach we were able to identify the structural frataxin homologue Fra (formerly YdhG) of Bacillus subtilis and to quantify its native iron-binding stoichiometry. Using recombinant proteins we could show in vitro that Fra is able to transfer iron onto the B. subtilis SUF system for iron-sulfur cluster biosynthesis. In a four-constituents reconstitution system (including SufU, SufS, Fra and CitB) we observed a Fra-dependent formation of a [4 Fe-4 S] cluster on SufU that could be efficiently transferred onto the target apo-aconitase (CitB). A Δfra deletion mutant showed a severe growth phenotype associated with a broadly disturbed iron homeostasis; this indicates that Fra is a central component of intracellular iron channeling in B. subtilis.
Assuntos
Bacillus subtilis/metabolismo , Proteínas de Ligação ao Ferro/metabolismo , Ferro/metabolismo , Bacillus subtilis/genética , Proteínas de Ligação ao Ferro/química , Proteínas de Ligação ao Ferro/genética , Espectrometria de Massas , Chaperonas Moleculares/metabolismo , Proteômica , FrataxinaRESUMO
Bacteria use three distinct systems for iron-sulfur (Fe/S) cluster biogenesis: the ISC, SUF, and NIF machineries. The ISC and SUF systems are widely distributed, and many bacteria possess both of them. In Escherichia coli, ISC is the major and constitutive system, whereas SUF is induced under iron starvation and/or oxidative stress. Genomic analysis of the Fe/S cluster biosynthesis genes in Bacillus subtilis suggests that this bacterium's genome encodes only a SUF system consisting of a sufCDSUB gene cluster and a distant sufA gene. Mutant analysis of the putative Fe/S scaffold genes sufU and sufA revealed that sufU is essential for growth under minimal standard conditions, but not sufA. The drastic growth retardation of a conditional mutant depleted of SufU was coupled with a severe reduction of aconitase and succinate dehydrogenase activities in total-cell lysates, suggesting a crucial function of SufU in Fe/S protein biogenesis. Recombinant SufU was devoid of Fe/S clusters after aerobic purification. Upon in vitro reconstitution, SufU bound an Fe/S cluster with up to approximately 1.5 Fe and S per monomer. The assembled Fe/S cluster could be transferred from SufU to the apo form of isopropylmalate isomerase Leu1, rapidly forming catalytically active [4Fe-4S]-containing holo-enzyme. In contrast to native SufU, its D43A variant carried a Fe/S cluster after aerobic purification, indicating that the cluster is stabilized by this mutation. Further, we show that apo-SufU is an activator of the cysteine desulfurase SufS by enhancing its activity about 40-fold in vitro. SufS-dependent formation of holo-SufU suggests that SufU functions as an Fe/S cluster scaffold protein tightly cooperating with the SufS cysteine desulfurase.
Assuntos
Bacillus subtilis/metabolismo , Regulação Bacteriana da Expressão Gênica/fisiologia , Proteínas Ferro-Enxofre/metabolismo , Bacillus subtilis/genética , Proteínas de Bactérias , Liases de Carbono-Enxofre/metabolismo , Clonagem Molecular , Ativação Enzimática , Ferro/metabolismo , Proteínas Ferro-Enxofre/genética , Isomerases/metabolismo , Enxofre/metabolismoRESUMO
We report an unusual reaction design in which a chiral bis-cyclometalated rhodium(iii) complex enables the stereocontrolled chemistry of photo-generated carbon-centered radicals and at the same time catalyzes an enantioselective sulfonyl radical addition to an alkene. Specifically, employing inexpensive and readily available Hantzsch esters as the photoredox mediator, Rh-coordinated prochiral radicals generated by a selective photoinduced single electron reduction are trapped by allyl sulfones in a highly stereocontrolled fashion, providing radical allylation products with up to 97% ee. The hereby formed fragmented sulfonyl radicals are utilized via an enantioselective radical addition to form chiral sulfones, which minimizes waste generation.
RESUMO
The organometallic tetraradical 1,2,4,5-[(eta)7-C7H7)V(all eta]5-C5H4)]4C6H2 has been prepared and structurally characterized. The isotropic EPR spectrum displays 29 a(51V) hyperfine lines, the intensity distribution slightly deviating from binomial. Exchange coupling therefore approaches the strong exchange limit, J(ortho) not equal to J(meta) not equal to J(para) greater or approximately 50 a(51V) with a(51V)= 0.0067 cm(-1). According to magnetic susceptometry, the interaction is antiferromagnetic. While redox splittings deltaE(1/2) are resolved for the four reduction steps this is not the case for oxidation.
Assuntos
Magnetismo , Compostos Organometálicos/química , Vanádio/química , Eletroquímica , Espectroscopia de Ressonância de Spin Eletrônica , Radicais Livres/química , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/síntese química , Oxirredução , Sensibilidade e EspecificidadeRESUMO
A highly reactive nickel catalyst comprising NiCl2(dppp) or NiCl2(dppe) with zinc powder, ZnI2 and Ph2PH, was applied in the isomerization of terminal alkenes to Z-2-alkenes. The double-bond geometry of the 2-alkene can be controlled via the reaction temperature to yield the 2-Z-alkenes in excellent yields and high Z-selectivities. The formation of other constitutional isomers, such as 3-alkenes, is suppressed on the basis of the proposed mechanism via a 1,2-hydride shift from the metal to the Ph2P ligand. The nickel-catalyzed isomerization reaction was then applied in the synthesis of (9Z,12Z)-tetradeca-9,12-dienyl acetate, a pheromone with a 2Z,5Z-diene subunit.
RESUMO
Thurincin H is a 31-residue, ribosomally synthesized bacteriocin originating from the thn operon of Bacillus thuringiensis SF361. It is the only known sactipeptide carrying four thioether bridges between four cysteines and the α-carbons of a serine, an asparagine and two threonine residues. By analysis of the thn operon and use of in vitro studies we now reveal that ThnB is a radical S-adenosylmethionine (SAM) enzyme containing two [4Fe-4S] clusters. Furthermore, we confirm the involvement of ThnB in the formation of the thioether bonds present within the structure of thurincin H. Finally, we show that the PqqD homologous N-terminal domain of ThnB is essential for maturation of the thurincin H precursor peptide, but not for the SAM cleavage activity of ThnB.
Assuntos
Bacteriocinas/metabolismo , Hidrolases/metabolismo , Sulfetos/metabolismo , Sequência de Aminoácidos , Bacillus thuringiensis/metabolismo , Bacteriocinas/química , Bacteriocinas/genética , Dados de Sequência Molecular , Óperon , Sulfetos/químicaRESUMO
Unprecedented imido phthalocyaninato complexes of pentavalent refractory metals [PcM(NR)Cl] (M = Mo, W, Re; R = tBu: 1, 3, 6, Mes: 2, 4, 7 or Ts: 5) have been synthesized by reductive cyclotetramerization of phthalonitrile in the presence of appropriate bis(imido) complexes of Mo, W and Re as templates. While d(1) Mo(V) and W(V) species 1-5 show distinctive EPR spectra corresponding to metal centered radicals with hyperfine coupling of two magnetically non-equivalent nitrogen atoms (4 equatorial and 1 axial N), corresponding d(2) Re(V) compounds 6 and 7 are diamagnetic. [PcMo(NtBu)Cl] 1 crystallizes from 1-chloronaphthalene in the tetragonal space group P4/n. The molecular structure reveals, that the metal center is located above the plane of the equatorial N4 and displaced towards the axial π-donor ligand. Due to the thermodynamic trans effect the Mo-Cl bond trans to the imido group is elongated to about 2.600(2) Å.
RESUMO
A unique series of halogenidoiron(III) complexes of the open-chain tetrapyrrolic ligand 2,2'-bidipyrrin (bpd) ([FeX(bdp)] X=F, Cl, Br, I) was prepared from simple pyrrolic and bipyrrolic precursors and iron chloride by a one-pot condensation/metalation strategy, followed by salt metathesis with CsF, LiBr, or NaI. Crystallographic analysis revealed that in all cases the 2,2'-bidipyrrin ligand is forced to reside in a helical conformation when bound to the iron atom. Whereas the extremely sensitive fluorido derivative was isolated as a CsF adduct and forms 1D polymeric chains in the solid state, the more stable chlorido, bromido, and iodido derivatives crystallize as discrete monomeric molecules with a distorted pentacoordinate iron(III) ion in an intermediate spin ground state. Magnetic susceptibility measurements and Mössbauer data of the compounds are in agreement with this interpretation. In solution, however, all the compounds are pentacoordinate with the iron atom in the high-spin (S=5/2) state and dynamic with respect to helix inversion. In the presence of air, the iron chelates react stepwise with the nucleophiles methanol and imidazolate at the tetrapyrrole terminal alpha,omega-positions, presumably through the hexacoordinate species [Fe(bdp)(MeOH)2]+ and [Fe(im)2-(bdp)](-), respectively. The successive increase of strain at these positions results in increasingly labile intermediates that spontaneously release the iron ion from the mono- or disubstituted tetrapyrrole ligands.
Assuntos
Pigmentos Biliares/química , Quelantes de Ferro/química , Pirróis/química , Cristalografia por Raios X , Espectroscopia de Ressonância Magnética , Magnetismo , Modelos Moleculares , Estrutura Molecular , SoluçõesRESUMO
A series of homoleptic complexes with non-innocent ligands derived from N,N'-bis(pentafluorophenyl)-o-phenylenediamine (H(2)(F)pda) are reported. [Ni(II)((F)sbqdi)(2)] (1), [Pd(II)((F)sbqdi)(2)] (2), [Co(II)((F)sbqdi)(2)] (3), and [Cu(II)((F)sbqdi)(2)] (4) were synthesized, where ((F)sbqdi)(1-) represents a radical anion formed by one-electron oxidation of the doubly deprotonated H2(F)pda. The oxidation states of ligands and metals in complexes 1-4 were assigned by single crystal X-ray crystallography performed at low temperatures. Complex 4 is the first Cu(II) complex where both o-phenylenediamine derived ligands are monoanionic radicals. The bulky N-C6F5 substituents force the complexes 1, 3, and 4 to adopt a twisted geometry (intermediate between square-planar and tetrahedral). The electronic structures of the neutral compounds 1-4 and of some of their cationic and/or anionic neighboring redox states were probed using EPR and UV-VIS-NIR spectroelectrochemistry. The twisted geometry of the complexes results in considerable changes in their electronic structures compared to the well known square-planar complexes while the strongly electron withdrawing N-C6F5 groups have a great influence on redox properties.