Isoprenoid biosynthesis via the methylerythritol phosphate pathway: the (E)-4-hydroxy-3-methylbut-2-enyl diphosphate reductase (LytB/IspH) from Escherichia coli is a [4Fe–4S] protein

AbstractThe last enzyme (LytB) of the methylerythritol phosphate pathway for isoprenoid biosynthesis catalyzes the reduction of (E)-4-hydroxy-3-methylbut-2-enyl diphosphate into isopentenyl diphosphate and dimethylallyl diphosphate. This enzyme possesses a dioxygen-sensitive [4Fe–4S] cluster. This prosthetic group was characterized in the Escherichia coli enzyme by UV/visible and electron paramagnetic resonance spectroscopy after reconstitution of the purified protein. Enzymatic activity required the presence of a reducing system such as flavodoxin/flavodoxin reductase/reduced nicotinamide adenine dinucleotide phosphate or the photoreduced deazaflavin radical

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS).

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.The EU-ROS consortium (COST Action BM1203) was supported by the European Cooperation in Science and Technology (COST). The present overview represents the final Action dissemination summarizing the major achievements of COST Action BM1203 (EU-ROS) as well as research news and personal views of its members. Some authors were also supported by COST Actions BM1005 (ENOG) and BM1307 (PROTEOSTASIS), as well as funding from the European Commission FP7 and H2020 programmes, and several national funding agencies

Electron paramagnetic resonance image reconstruction with total variation and curvelets regularization

Spatial electron paramagnetic resonance imaging (EPRI) is a recent method to localize and characterize free radicals in vivo or in vitro, leading to applications in material and biomedical sciences. To improve the quality of the reconstruction obtained by EPRI, a variational method is proposed to inverse the image formation model. It is based on a least-square data-fidelity term and the total variation and Besov seminorm for the regularization term. To fully comprehend the Besov seminorm, an implementation using the curvelet transform and the L1 norm enforcing the sparsity is proposed. It allows our model to reconstruct both image where acquisition information are missing and image with details in textured areas, thus opening possibilities to reduce acquisition times. To implement the minimization problem using the algorithm developed by Chambolle and Pock, a thorough analysis of the direct model is undertaken and the latter is inverted while avoiding the use of filtered backprojection (FBP) and of non-uniform Fourier transform. Numerical experiments are carried out on simulated data, where the proposed model outperforms both visually and quantitatively the classical model using deconvolution and FBP. Improved reconstructions on real data, acquired on an irradiated distal phalanx, were successfully obtained

Electron paramagnetic resonance image reconstruction with total variation and curvelets regularization

Spatial electron paramagnetic resonance imaging (EPRI) is a recent method to localize and characterize free radicals in vivo or in vitro, leading to applications in material and biomedical sciences. To improve the quality of the reconstruction obtained by EPRI, a variational method is proposed to inverse the image formation model. It is based on a least-square data-fidelity term and the total variation and Besov seminorm for the regularization term. To fully comprehend the Besov seminorm, an implementation using the curvelet transform and the L1 norm enforcing the sparsity is proposed. It allows our model to reconstruct both image where acquisition information are missing and image with details in textured areas, thus opening possibilities to reduce acquisition times. To implement the minimization problem using the algorithm developed by Chambolle and Pock, a thorough analysis of the direct model is undertaken and the latter is inverted while avoiding the use of filtered backprojection (FBP) and of non-uniform Fourier transform. Numerical experiments are carried out on simulated data, where the proposed model outperforms both visually and quantitatively the classical model using deconvolution and FBP. Improved reconstructions on real data, acquired on an irradiated distal phalanx, were successfully obtained

Iron and manganese surface complex formation with extracted lignin. Part 2: characterisation of magnetic interaction between transition metal and quinonic radical by EPR microwave power saturation experiments

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Estimation of spectrum parameters for Quantitative EPR in the derivative limit

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Iron and manganese surface complex formation with extracted lignin. Part 2: characterisation of magnetic interaction between transition metal and quinonic radical by EPR microwave power saturation experiments

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Multifrequency High-Field EPR Study of Binuclear Mn(III)Mn(IV) Complexes

International audienceThe results from a multifrequency high-field EPR study of five di-μ-oxo bridged mixed-valence binuclear Mn(III)Mn(IV) complexes are reported. Spectra were obtained at 9, 95, and 285 GHz. The g anisotropy was unambiguously observable at 285 GHz. Hyperfine and g tensor values were estimated using spectral simulation procedures that cyclically and simultaneously fit the multifrequency data. In all five cases, the g tensors of the mixed-valence complexes were found to be rhombic. The g tensors were analyzed using the vector projection model. Most, but not all, of the g anisotropy originates from the Mn(III) center. The rhombic g tensors result from the low symmetry of the manganese centers. The size of the effective g anisotropy for a given complex was found to be a linear function of the average bond distance between the manganese and axial nitrogens. This relationship can be understood in terms of the influence of tetragonal distortion on the electronic levels of the Mn(III) center. The frequency-dependent line broadening observed in these mixed-valence complexes is explained in terms of the relationship between g anisotropy and structure

Parameter Estimation for Quantitative EPR Spectroscopy

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