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1.
Nbp35 and Cfd1 are prototypical members of the MRP/Nbp35 class of iron-sulfur (FeS) cluster scaffolds that function to assemble nascent FeS clusters for transfer to FeS-requiring enzymes. Both proteins contain a conserved NTPase domain that genetic studies have demonstrated is essential for their cluster assembly activity inside the cell. It was recently reported that these proteins possess no or very low nucleotide hydrolysis activity in vitro, and thus the role of the NTPase domain in cluster biogenesis has remained uncertain. We have reexamined the NTPase activity of Nbp35, Cfd1, and their complex. Using in vitro assays and site-directed mutagenesis, we demonstrate that the Nbp35 homodimer and the Nbp35-Cfd1 heterodimer are ATPases, whereas the Cfd1 homodimer exhibited no or very low ATPase activity. We ruled out the possibility that the observed ATP hydrolysis activity might result from a contaminating ATPase by showing that mutation of key active site residues reduced activity to background levels. Finally, we demonstrate that the fluorescent ATP analog 2′/3′-O-(N′-methylanthraniloyl)-ATP (mantATP) binds stoichiometrically to Nbp35 with a KD = 15.6 μm and that an Nbp35 mutant deficient in ATP hydrolysis activity also displays an increased KD for mantATP. Together, our results demonstrate that the cytosolic iron-sulfur cluster assembly scaffold is an ATPase and pave the way for interrogating the role of nucleotide hydrolysis in cluster biogenesis by this large family of cluster scaffolding proteins found across all domains of life.  相似文献   
2.
In this research, kinetics of Cr(VI) reduction by iron filings was investigated through a batch study in seven different soils. Chromate reduction experiments were carried out for initial Cr(VI) concentrations ranging from 20 to 100 mgkg?1 and iron filings dosage of 0 to 5% w/w. The experimental data were analyzed using various kinetic models including zero-order, pseudo first-order, power function, Elovich, and diffusion parabolic. Results showed that the Cr(VI) reduction efficiency in the presence of all studied soils increased with increasing iron filings dosage and decreased with increasing the initial Cr(VI) concentration. The reaction rates considerably depended on pH and were higher in acidic soils. The diffusion parabolic model was the best kinetic model as evidenced by the highest determination coefficient (r2) and the lowest standard error of the estimate (SE). The rate-limiting step(s) may be transport of chromate anions across a liquid film at the interface of soil-liquid, transport in liquid-filled macropores of iron filings aggregates, or diffusion in micropores and along the particle's surface.  相似文献   
3.
In this study, we cultivated from subsurface sediments an anaerobic clostridial consortium that was composed of a fermentative Fe-reducer Clostridium species (designated as strain FGH) and a novel sulfate-reducing bacterium belonging to the clostridia family Vellionellaceae (designated as strain RU4). In pure culture, Clostridium sp. strain FGH mediated the reductive dissolution/transformation of iron oxides during growth on peptone. When Clostridium sp. FGH was grown with strain RU4 on peptone, the rates of iron oxide reduction were significantly higher. Iron reduction by the consortium was mediated by multiple mechanisms, including biotic reduction by Clostridium sp. FGH and biotic/abiotic reactions involving biogenic sulfide formed by strain RU4. The Clostridium sp. FGH produced hydrogen during fermentation, and the presence of hydrogen inhibited growth and iron reduction activity. The sulfate-reducing partner strain RU4 was stimulated by the presence of H2and generated reactive sulfide which promoted the chemical reduction of the iron oxides. Characterization of Fe(II) mineral products showed the formation of nanoparticulate magnetite during ferrihydrite reduction, and the precipitation of iron sulfides during goethite and hematite reduction. The results suggest an important pathway for iron reduction and secondary mineralization by fermentative sulfate-reducing microbial consortia through syntrophy-driven biotic/abiotic reactions with biogenic sulfide.

Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.  相似文献   

4.
The dissociation constants for the binding of ferric enterobactin with FepA and FecA are quantitated with displacement experiments. It is found that K d for FepA is 12 times lower than the one for FecA. This indicates that FepA is an high-affinity receptor while FecA binds ferric enterobactin with a lower affinity. Monoclonal antibodies specific for binding epitopes of FepA inhibit the binding of ferric enterobactin with purified FepA. These same antibodies do not inhibit the binding of ferric enterobactin with purified FecA. This indicates that the binding epitopes in FecA and FepA are different.  相似文献   
5.
Sphaerotilus natans is a neutrophilic sheath-forming microorganism from the Sphaerotilus-Leptothrix group of iron-related bacteria, known to form bacteriogenic iron oxides (BIOS) frequently deposited on cell surfaces as well as on sheaths and extracellular polymeric substances. S. natans has been reported to be an excellent sorbent for inorganic pollutants, either due to direct sorption onto biological surfaces or due to sorption onto BIOS. However, its filaments can cause bulking problems in wastewater treatment plants. This article promotes the potential applications of Sphaerotilus natans in bioremediation by reviewing its physiology and the fundamental understanding of sheath-forming mechanisms as well as iron biomineralization processes.  相似文献   
6.
Spin-trapping techniques combined with electron paramagnetic resonance (EPR) spectroscopy to measure nitric oxide (·NO) production were compared in the ischemic-reperfused myocardium for the first time, using both aqueous-soluble and lipophilic complexes of reduced iron (Fe) with dithiocarbamate derivatives. The aqueous-soluble complex of Fe and N-methyl-D-glucamine dithiocarbamate (MGD) formed MGD2-Fe-NO complex with a characteristic triplet EPR signal (aN12.5 G and giso = 2.04) at room temperature, in native isolated rat hearts following 40 min global ischemia and 15 min reperfusion. Diethyldithiocarbamate (DETC) and Fe formed in ischemic-reperfused myocardium the lipophilic DETC2-Fe-NO complex exhibiting an EPR signal (g = 2.04 and g = 2.02 at 77K) with a triplet hyperfine structure at g. Dithiocarbamate-Fe-NO complexes detected by both trapping agents were abolished by the ·NO synthase inhibitor, NG-nitro-L-arginine methyl ester. Quantitatively, both trapping procedures provi ded similar values for tissue ·NO production, which were observed primarily during ischemia. Postischemic hemodynamic recovery of the heart was not affected by the trapping procedure. (Mol Cell Biochem 175: 91–97, 1997)  相似文献   
7.
A hybrid approach combining life cycle assessment and input‐output analysis was used to demonstrate the economic and environmental benefits of current and future improvements in agricultural and industrial technologies for ethanol production in Brazilian biorefineries. In this article, three main scenarios were evaluated: first‐generation ethanol production with the average current technology; the improved current technology; and the integration of improved first‐ and second‐generation ethanol production. For the improved first‐generation scenario, a US$1 million increase in ethanol demand can give rise to US$2.5 million of total economic activity in the Brazilian economy when direct and indirect purchases of inputs are considered. This value is slightly higher than the economic activity (US$1.8 million) for an energy equivalent amount of gasoline. The integration of first‐ and second‐generation technologies significantly reduces the total greenhouse gas emissions of ethanol production: 14.6 versus 86.4 grams of carbon dioxide equivalent per megajoule (g CO2‐eq/MJ) for gasoline. Moreover, emissions of ethanol can be negative (–10.5 g CO2‐eq/MJ) when the system boundary is expanded to account for surplus bioelectricity by displacement of natural gas thermal electricity generation considering electricity produced in first‐generation optimized biorefineries.  相似文献   
8.
This study aims to explore the ability of magnetic resonance imaging (MRI) in mucin 1 (MUC1) modified superparamagnetic iron oxide nanoparticle (SPION) targeting human pancreatic cancer (PC). The MUC1 target-directed probe was prepared through MUC1 conjugated to SPION using the chemical method to assess its physiochemical characteristics, including hydration diameter, surface charge, and magnetic resonance signal. The cytotoxicity of MUC1-USPION was verified by MTS assay. BxPC-3 was cultured with MUC1-USPION and SPION in different concentrations. The combined condition of the targeted probes and cells were observed through Prussian blue staining. The nude mice model of pancreatic cancer was established to investigate the application of the probe. MRI was performed to determine the intensity of the signal of the transplanted tumor, while immunohistochemistry and Western blot analysis were performed to detect the expression of MUC1 after taking the transplanted tumor specimen. The particle size of the prepared molecular probe was 63.5 ± 3.2 nm, and the surface charge was 10.2 mV. Furthermore, the probe solution could significantly reduce the MRI at T2, and the magnetic resonance transverse relaxation rate (ΔR2) has a linear relationship with the concentration of iron in the solution. The cell viability of MUC1-USPION in different concentrations revealed no statistical difference, according to the MTS assay. In vitro, the MRI demonstrated decreased T2WI signal intensity in both groups, especially the targeting group. In vivo, MUC1 could selectively accumulate in the nude mice model, and significantly reduce the T2 signal strength. In subsequent experiments, the expression of MUC1 was high in pancreatic cancer tissues, but low in normal pancreatic tissues, as determined by immunohistochemistry and Western blot analysis. The prepared samples can be combined with pancreatic cancer tissue specificity by in vivo imaging, providing reliable early in vivo imaging data for disease diagnosis.  相似文献   
9.
In order to establish infection, pathogenic bacteria must obtain essential nutrients such as iron. Under acidic and/or anaerobic conditions, most bacteria utilize the Feo system in order to acquire ferrous iron (Fe2+) from their host environment. The mechanism of this process, including its regulation, remains poorly understood. In this work, we have determined the crystal structure of FeoA from the nosocomial agent Klebsiella pneumoniae (KpFeoA). Our structure reveals an SH3-like domain that mediates interactions between neighboring polypeptides via hydrophobic intercalations into a Leu-rich surface ridge. Using docking of a small peptide corresponding to a postulated FeoB partner binding site, we demonstrate that KpFeoA can assume both “open” and “closed” conformations, controlled by binding at this Leu-rich ridge. We propose a model in which a “C-shaped” clamp along the FeoA surface mediates interactions with its partner protein, FeoB. These findings are the first to demonstrate atomic-level details of FeoA-based protein-protein interactions and provide a framework for testing FeoA-FeoB interactions, which could be exploited for future antibiotic developments.  相似文献   
10.
TonB protein couples cytoplasmic membrane electrochemical potential to active transport of iron-siderophore complexes and vitamin B12 through high-affinity outer membrane receptors of Gram-negative bacteria. The mechanism of energy transduction remains to be determined, but important concepts have already begun to emerge. Consistent with its function, TonB is anchored in the cytoplasmic membrane by its uncleaved amino terminus while largely occupying the periplasm. Both the connection to the cytoplasmic membrane and the amino acid sequences of the anchor are essential for activity. TonB directly associates with a number of envelope proteins, among them the outer membrane receptors and cytoplasmic membrane protein ExbB. ExbB and TonB interact through their respective transmembrane domains. ExbB is proposed to recycle TonB to an active conformation following energy transduction to the outer membrane. TonB most likely associates with the outer membrane receptors through its carboxy terminus, which is required for function. In contrast, the novel prolinerich region of TonB can be deleted without affecting function. A model that incorporates this information, as well as tempered speculation, is presented.  相似文献   
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