Genetic engineering in Streptomyces roseosporus to produce hybrid lipopeptide antibiotics

Daptomycin is a lipopeptide antibiotic produced by a nonribosomal peptide synthetase (NRPS) in Streptomyces roseosporus. The holoenzyme is composed of three subunits, encoded by the dptA, dptBC, and dptD genes, each responsible for incorporating particular amino acids into the peptide. We introduced expression plasmids carrying dptD or NRPS genes encoding subunits from two related lipopeptide biosynthetic pathways into a daptomycin nonproducing strain of S. roseosporus harboring a deletion of dptD. All constructs successfully complemented the deletion in trans, generating three peptide cores related to daptomycin. When these were coupled with incomplete methylation of 1 amino acid and natural variation in the lipid side chain, 18 lipopeptides were generated. Substantial amounts of nine of these compounds were readily obtained by fermentation, and all displayed antibacterial activity against gram-positive pathogens.     

Suppression of nitric oxide production in mouse macrophages by soybean flavonoids accumulated in response to nitroprusside and fungal elicitation

Background

The anti-inflammatory properties of some flavonoids have been attributed to their ability to inhibit the production of NO by activated macrophages. Soybean cotyledons accumulate certain flavonoids following elicitation with an extract of the fungal pathogen Diaporthe phaseolorum f. sp. meridionalis (Dpm). Sodium nitroprusside (SNP), a nitric oxide donor, can substitute for Dpm in inducing flavonoid production. In this study, we investigated the effect of flavonoid-containing diffusates obtained from Dpm- and SNP-elicited soybean cotyledons on NO production by lipopolysaccharide (LPS)- and LPS plus interferon-γ (IFNγ)-activated murine macrophages.

Results

Significant inhibition of NO production, measured as nitrite formation, was observed when macrophages were activated in the presence of soybean diffusates from Dpm- or SNP-elicited cotyledons. This inhibition was dependent on the duration of exposure to the elicitor. Daidzein, genistein, luteolin and apigenin, the main flavonoids present in diffusates of elicited cotyledons, suppressed the NO production by LPS + IFNγ activated macrophages in a concentration-dependent manner, with IC₅₀ values of 81.4 μM, 34.5 μM, 38.6 μM and 10.4 μM respectively. For macrophages activated with LPS alone, the IC₅₀ values were 40.0 μM, 16.6 μM, 10.4 μM and 2.8 μM, respectively. Western blot analysis showed that iNOS expression was not affected by daidzein, was reduced by genistein, and was abolished by apigenin, luteolin and Dpm- and SNP-soybean diffusates at concentrations that significantly inhibited NO production by activated macrophages.

Conclusions

These results suggest that the suppressive effect of flavonoids on iNOS expression could account for the potent inhibitory effect of Dpm- and SNP-diffusates on NO production by activated macrophages. Since the physiological concentration of flavonoids in plants is normally low, the treatment of soybean tissues with SNP may provide a simple method for substantially increasing the concentration of metabolites that are beneficial for the treatment of chronic inflammatory diseases associated with NO production.

     

Cyclohexadienone diazeniumdiolates from nitric oxide addition to phenolates

Sterically hindered phenols react with nitric oxide under basic condititons to give either cyclohexadienone diazeniumdiolates or oximates. Phenols with 2,6-di-tert-butyl and 4-methyl (butylated hydroxy toluene, BHT), 4-ethyl, or 4-methoxy methylene substituents yield the corresponding 2,6-di-tert-butyl-2, 5-cyclohexadienone-4-alkyl-4-diazeniumdiolate salts (4-methyl 1a, 4-ethyl 3a, 4-methoxymethylene 5a). Phenols with 2,6-di-tert-butyl and 4-methylene (2,6-di-tert-butylphenol) substituents yield 4-methoxymethylenediazeniumdiolate (5a) together with 2, 6-di-tert-butyl benzoquinone oximate (6a), while phenols with 2, 6-di-tert-butyl and 4-methylenedimethylamino or hydrogen substituents yield exclusively 2,6-di-tert-butyl benzoquinone oximate (6a). Alkylation of the silver salts of 1a, or treating the O(2)-protonated diazeniumdiolate with diazomethane, both yield mixtures of O(1)- and O(2)-methylated isomers. All the compounds exhibit exothermic thermal decomposition except the quinuclidinium (1e, 3e, 5e) and triethylenediammonium (1f) salts which decompose endothermically. Three of the compounds namely "O(2)-protonated" (Z)-1-[4-(2, 6-di-tert-butyl-4-methyl-cyclohexadienonyl)]diazen-1-ium+ ++-1, 2-diolinic acid (1b), O(2)-methyl (Z)-1-[4-(2, 6-di-tert-butyl-4-methyl-cyclohexadienonyl)]diazen-1-ium+ ++-1,2-diolate (1c), and "O(2)-protonated" (Z)-1-[4-(2, 6-di-tert-butyl-4-methoxymethylenecyclohexadienonyl)]diazen- 1-ium-1, 2-diolinic acid (5b) were characterized by single-crystal X-ray diffraction studies. The diazeniumdiolate framework in all the structures is coplanar with considerable pi-bonding delocalized over the O-N-N-O framework.     

Motexafin gadolinium reacts with ascorbate to produce reactive oxygen species

Motexafin gadolinium (MGd) oxidizes ascorbate, in neutral buffer and in cell culture, forming reactive oxygen species and a coordination polymer with oxalate.     

Discovery of nitric oxide in marine ecological system and the chemical characteristics of nitric oxide

Nitric oxide was discovered in both the lab and the alga culture pond of Daya Bay (1―300 m3) before the growth of alga reached the maximum. The results included: (1) NO was detected before the growth of alga reached the maximum in the case of red tide alga and food alga, and the concentration of NO decreased rapidly after the growth maximum; (2) the curve between NO con-centration and time indicated that the concentration of NO in the daytime was more than that at night, and the maximal concentration of NO appeared in the midday (1―3 pm); (3) the growth of alga reached the maximum in the alga culture pond of Daya Bay in about 8―10 d, and NO was discovered in 5―7 d; (4) the measured NO concentration was 10-9 mol/L, 10-9―10-8 mol/L, and 10-8 mol/L for Haeterosigma akashiwo, mixed alga in Daya Bay and Chaetoceros Curvisetus individually; (5) the relation of illumination with NO production was discussed.     

Reduction of nitric oxide to elemental nitrogen byThiobacillus Denitrificans

A need exists for new technology for the disposal of concentrated NO_x streams obtained from certain regenerable, dry scrubbing processes, such as the NOXSO process, and the removal and disposal of NO_x from more dilute gas streams produced by nitric acid plants. It has been demonstrated that the facultative anaerobe and autotroph, Thiobacillus denitrificans, may be cultured anaerobically in batch reactors using NO (g) as a terminal electron acceptor. Thiosulfate served as an energy source, CO₂ (g) as a carbon source, and ammonium ion as a source of reduced nitrogen. The growth of T.denitrificans was indicated by depletion of thiosulfate and ammonium ion and the accumulation of biomass. The feed gas consisted of 5000 ppmv NO, 5%, CO₂, and balance nitrogen. The NO concentration in the outlet gas was typically 200 ppmv.     

Generic nitric oxide (NO) generating surface by immobilizing organoselenium species via layer-by-layer assembly

A universal nitric oxide (NO) generating surface is assembled via Layer-by-Layer (LbL) deposition of sodium alginate (Alg) and organoselenium modified polyethyleneimine (SePEI) on quartz and polymeric substrates. The immobilized SePEI species is capable of catalytically decomposing S-nitrosothiol species (RSNO) to NO in the presence of thiol reducing agents (e.g., glutathione, cysteine, etc.). The stepwise buildup of the multilayer films is monitored by UV-vis spectroscopy, SEM and surface contact angle measurements. X-ray photoelectron spectroscopy is used to study the stoichiometry between the polyanion and polycation, and also the presence of Se in the catalytic LbL film. A reductive annealing process is necessary to improve the stability of freshly coated multilayer films via chain rearrangement. Chemiluminescence measurements illustrate the ability of the LbL films to generate NO from S-nitrosoglutathione (GSNO) in the presence of glutathione (GSH). Enhanced NO fluxes can be achieved by increasing the number of catalytic (SePEI/Alg) bilayers coated on the substrates. Nitric oxide generation is observed even after prolonged contact with sheep whole blood. Preliminary applications of this LbL on silicone rubber tubings and polyurethane catheters reveal similar NO generation behavior from these biomedical grade polymeric substrates.     

Characterization of iron dinitrosyl species formed in the reaction of nitric oxide with a biological Rieske center

Reactions of nitric oxide with cysteine-ligated iron-sulfur cluster proteins typically result in disassembly of the iron-sulfur core and formation of dinitrosyl iron complexes (DNICs). Here we report the first evidence that DNICs also form in the reaction of NO with Rieske-type [2Fe-2S] clusters. Upon treatment of a Rieske protein, component C of toluene/o-xylene monooxygenase from Pseudomonas sp. OX1, with an excess of NO(g) or NO-generators S-nitroso-N-acetyl-D,L-pencillamine and diethylamine NONOate, the absorbance bands of the [2Fe-2S] cluster are extinguished and replaced by a new feature that slowly grows in at 367 nm. Analysis of the reaction products by electron paramagnetic resonance, M?ssbauer, and nuclear resonance vibrational spectroscopy reveals that the primary product of the reaction is a thiolate-bridged diiron tetranitrosyl species, [Fe(2)(μ-SCys)(2)(NO)(4)], having a Roussin's red ester (RRE) formula, and that mononuclear DNICs account for only a minor fraction of nitrosylated iron. Reduction of this RRE reaction product with sodium dithionite produces the one-electron-reduced RRE, having absorptions at 640 and 960 nm. These results demonstrate that NO reacts readily with a Rieske center in a protein and suggest that dinuclear RRE species, not mononuclear DNICs, may be the primary iron dinitrosyl species responsible for the pathological and physiological effects of nitric oxide in such systems in biology.     

Amplified nitric oxide photorelease in DNA proximity

A novel bichromophoric conjugate integrating a NO photodonor and a DNA intercalator in its molecular skeleton, allows the light-controlled NO delivery nearby DNA and amplifies NO release via effective photoinduced energy transfer mechanism.     

Detection of nitric oxide in single cells

Nitric oxide (NO) is endogenously generated by nitric oxide synthase (NOS) enzymes and is involved in a surprisingly wide range of biological functions. As efforts are made to elucidate the regulatory mechanisms of NOS expression and function, there is increasing interest in following NOS activity directly by monitoring NO production. Additionally, spatial and temporal measurements of NO are important for understanding its function and metabolism. In this work, developments in technology enabling NO detection in biological systems are reviewed. Measuring NO at single cell levels is important as NOS is heterogeneously distributed; however, such measurements are difficult as physiological NO levels are in the low nanomolar to low micromolar range. Here, three categories of analytical techniques enabling NO detection at single cell levels are highlighted: fluorescence microscopy, capillary electrophoresis with laser induced fluorescence detection, and electrochemistry. For each, the basic principles, performance, applications, figures of merits and limitations are presented in terms of single cell NO detection.     

Identification of nitrogen-containing species obtained by nitric oxide adsorption on the surface of model gold catalysts

Nitric oxide adsorption at 300–500 K on gold particles supported on an alumina film has been investigated for the first time by in situ X-ray photoelectron spectroscopy. Two nitrogen-containing adsorption species can form on the surface of gold particles. By test experiments on NO adsorption on the stepped face (533) of a gold single crystal, these species have been identified as adsorbed nitrogen atoms (which are detected throughout the temperature range examined) and a surface complex with N₂O stoichiometry (which is stable in a narrow temperature range of 325–425 K).     

A novel precursor system and its application to produce tin doped indium oxide

A new type of precursor has been developed by molecular design and synthesised to produce tin doped indium oxide (ITO). The precursor consists of a newly developed bimetallic indium tin alkoxide, Me(2)In(O(t)Bu)(3)Sn (Me = CH(3), O(t)Bu = OC(CH(3))(3)), which is in equilibrium with an excess of Me(2)In(O(t)Bu). This quasi single-source precursor is applied in a sol-gel process to produce powders and coatings of ITO using a one-step heat treatment process under an inert atmosphere. The main advantage of this system is the simple heat treatment that leads to the disproportionation of the bivalent Sn(II) precursor into Sn(IV) and metallic tin, resulting in an overall reduced state of the metal in the final tin doped indium oxide (ITO) material, hence avoiding the usually necessary reduction step. Solid state (119)Sn-NMR measurements of powder samples confirm the appearance of Sn(II) in an amorphous gel state and of metallic tin after annealing under nitrogen. The corresponding preparation of ITO coatings by spin coating on glass leads to transparent conductive layers with a high transmittance of visible light and a low electrical resistivity without the necessity of a reduction step.     

Hydrogenation of styrene oxide in the presence of supported platinum catalysts to produce 2-phenylethanol

Gas-phase hydrogenation of styrene oxide was investigated using platinum catalysts deposited on magnesia, γ-alumina and activated carbon (AC), at atmospheric pressure and within a wide range of temperature (348–398 K). In order to correlate the chemical and textural properties with the catalytic activity, all catalysts were characterized by several techniques such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), H₂-temperature-programmed desorption (TPD) N₂ physisorption and H₂ chemisorption. Obtained results indicate that the catalytic activity and the selectivity were affected by the nature of the support. In the presence of MgO or activated carbon, as supports, the main product was 2-phenylethanol (2-PEA). However, when the support was γ-alumina, the main product was phenylacetaldehyde (PAD). The basic character of the support led to the formation of the less substituted alcohol (2-PEA). This was obtained at high conversion (85%) with practically total selectivity (around 99%). However, more acid support such as γ-alumina led to the formation of the more substituted alcohol 1-phenylethanol (1-PEA) and phenylacetaldehyde, mainly due to the isomerisation of the epoxide. Consequently, the acid–base character of the support plays an important role in the selectivity of this reaction.     

IR laser induced UV fluorescence in nitric oxide

We observe UV fluorescence from a gas cell containing NO and Ar, when irradiated by a CO laser line, coincident with an NO fundamental. The power density generated cw by the CO laser does not exceed 1 $\text{kW}\text{cm}{}^2$ in the focal area. It is suggested that V-V pumping is responsible for exciting the NO X ²Π up to υ ≈ 30 from where collisional transfer into A ²Σ and B ²Π is possible.     

Reaction kinetics of the addition of atomic sulfur to nitric oxide

The reaction of S((3)P(J)) with NO ((2)Pi) in an Ar bath gas has been studied by the laser photolysis-resonance fluorescence technique over 300-810 K at pressures from 60 to 800 mbar. The observed second-order rate constants are close to the low-pressure limit. Fitting of Troe's formalism to experiment, with an estimated F(cent) = 0.78 exp(-T/7445) and k(infinity) given subsequently, yields k(0) = (6.2+/-0.6) x 10(-33) exp(+ (940+/-40)/T) cm(6) molecule(-2) s(-1). Error limits are +/-25%. A theoretical analysis of this value suggests that the average energy transferred during collisions between Ar and the excited intermediate is DeltaE = -360(-160) (+90) cm(-1). Over 300-800 K, the high-pressure limit is predicted to be k(infinity) = 2.2 x 10(-10) (T/300)(0.24) cm(3) molecule(-1) s(-1). Doublet and quartet adducts between S and NO were characterized via CBS-QB3 theory. The kinetic data can be rationalized with SNO ((2)A(')) as the major product, and an ab initio estimate of Delta(f)H(298) for SNO is 176+/-8 kJ mol(-1).     

Enhanced flow injection analysis for measurements of S-nitrosothiols species in biological samples using highly selective amperometric nitric oxide sensor

A highly selective nitric oxide(NO) sensor is fabricated and applied to devise an enhanced flow injection analysis(FIA) system for S-nitrosothiols(RSNOs) measurement in biological samples.The NO sensor is prepared using a polytetrafluoroethylene(PTFE) gas-permeable membrane loaded with Teflon AF? solution,a copolymer of tetrafluoroethylene and 2,2-bis(trifluoroethylene)-4,5-difluoro -l,3-dioxole,to improve selectivity.This method is much simpler and possesses good performance over a wide range of RSNOs concentrations.Standard deviation for three parallel measurements of blood plasma is 4.0%.The use of the gas sensing configuration as the detector enhances selectivity of the FIA measurement vs.using less selective electrochemical detectors that do not use PTFE/Teflon type outer membranes.     

Oxygen atom transfer promoted nitrate to nitric oxide transformation: a step-wise reduction of nitrate → nitrite → nitric oxide

Nitrate reductases (NRs) are molybdoenzymes that reduce nitrate (NO₃⁻) to nitrite (NO₂⁻) in both mammals and plants. In mammals, the salival microbes take part in the generation of the NO₂⁻ from NO₃⁻, which further produces nitric oxide (NO) either in acid-induced NO₂⁻ reduction or in the presence of nitrite reductases (NiRs). Here, we report a new approach of VCl₃ (V³⁺ ion source) induced step-wise reduction of NO₃⁻ in a Co^II-nitrato complex, [(12-TMC)Co^II(NO₃⁻)]⁺ (2,{Co^II–NO₃⁻}), to a Co^III–nitrosyl complex, [(12-TMC)Co^III(NO)]²⁺ (4,{CoNO}⁸), bearing an N-tetramethylated cyclam (TMC) ligand. The VCl₃ inspired reduction of NO₃⁻ to NO is believed to occur in two consecutive oxygen atom transfer (OAT) reactions, i.e., OAT-1 = NO₃⁻ → NO₂⁻ (r₁) and OAT-2 = NO₂⁻ → NO (r₂). In these OAT reactions, VCl₃ functions as an O-atom abstracting species, and the reaction of 2 with VCl₃ produces a Co^III-nitrosyl ({CoNO}⁸) with V^V-Oxo ({V^V O}³⁺) species, via a proposed Co^II-nitrito (3, {Co^II–NO₂⁻}) intermediate species. Further, in a separate experiment, we explored the reaction of isolated complex 3 with VCl₃, which showed the generation of 4 with V^V-Oxo, validating our proposed reaction sequences of OAT reactions. We ensured and characterized 3 using VCl₃ as a limiting reagent, as the second-order rate constant of OAT-2 (k₂^/) is found to be ∼1420 times faster than that of the OAT-1 (k₂) reaction. Binding constant (K_b) calculations also support our proposition of NO₃⁻ to NO transformation in two successive OAT reactions, as K_{b(Co^II–NO2⁻)} is higher than K_{b(Co^II–NO3⁻)}, hence the reaction moves in the forward direction (OAT-1). However, K_{b(Co^II–NO2⁻)} is comparable to K_b{CoNO}⁸, and therefore sequenced the second OAT reaction (OAT-2). Mechanistic investigations of these reactions using ¹⁵N-labeled-¹⁵NO₃⁻ and ¹⁵NO₂⁻ revealed that the N-atom in the {CoNO}⁸ is derived from NO₃⁻ ligand. This work highlights the first-ever report of VCl₃ induced step-wise NO₃⁻ reduction (NRs activity) followed by the OAT induced NO₂⁻ reduction and then the generation of Co-nitrosyl species {CoNO}⁸.

Single metal-induced reduction of NO₃⁻ → {NO₂⁻} → NO via oxygen atom transfer reaction.     

Investigation on binding of nitric oxide to horseradish peroxidase by absorption spectrometry

Binding of nitric oxide to horseradish peroxidase (HRP) has been investigated by absorption spectrometry in 0.2 M anaerobic phosphate buffer solution (pH 7.4). Based on this binding equilibrium, a model equation for evaluating the binding constant of nitric oxide to HRP is developed and the binding constant is calculated to be (1.55 ± 0.06) × 10⁴ M^?1, indicating that HRP can form a stable complex with nitric oxide. The type of inhibition by nitric oxide is validated on the basis of studying initial reaction rates of HRP-catalyzed oxidation of guaiacol in the presence of hydrogen peroxide and nitric oxide. The inhibition mechanism is found to follow an apparent non-competitive inhibition by Lineweaver–Burk method. Based on this kinetic mechanism, the binding constant is also calculated to be (5.22 ± 0.06) × 10⁴ M^?1. The values of the binding constant determined by the two methods are almost identical. The non-competitive inhibition model is also applicable to studying the effect of nitric oxide on other metalloenzymes, which catalyze the two-substrate reaction with the “ping-pong” mechanism.