ORCID Profile
0000-0003-1828-7700
Current Organisation
University of Oxford
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Publisher: Informa UK Limited
Date: 19-08-2018
Publisher: American Chemical Society (ACS)
Date: 24-07-2017
DOI: 10.1021/JACS.7B05386
Publisher: American Chemical Society (ACS)
Date: 06-02-2018
DOI: 10.1021/JACS.7B11056
Abstract: Cytochrome P450 (CYP) monooxygenases catalyze the oxidation of chemically inert carbon-hydrogen bonds in erse endogenous and exogenous organic compounds by atmospheric oxygen. This C-H bond oxy-functionalization activity has huge potential in biotechnological applications. Class I CYPs receive the two electrons required for oxygen activation from NAD(P)H via a ferredoxin reductase and ferredoxin. The interaction of Class I CYPs with their cognate ferredoxin is specific. In order to reconstitute the activity of erse CYPs, structural characterization of CYP-ferredoxin complexes is necessary, but little structural information is available. Here we report a structural model of such a complex (CYP199A2-HaPux) in frozen solution derived from distance and orientation restraints gathered by the EPR technique of orientation-selective double electron-electron resonance (os-DEER). The long-lived oscillations in the os-DEER spectra were well modeled by a single orientation of the CYP199A2-HaPux complex. The structure is different from the two known Class I CYP-Fdx structures: CYP11A1-Adx and CYP101A1-Pdx. At the protein interface, HaPux residues in the [Fe
Publisher: Wiley
Date: 27-07-2015
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP06096F
Abstract: Analysis of orientation-selective DEER measurements using Cu( ii ) centres in a series of molecules demonstrates its limits and capabilities in structure elucidation.
Publisher: American Chemical Society (ACS)
Date: 15-10-2023
DOI: 10.1021/JACS.3C04685
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP01787A
Abstract: The unique combination of EPR, DFT and novel large-scale simulation methods provides information on exchange coupling between metal centers in molecular wires.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CP04444A
Abstract: Ladder formation and planarisation do not enhance delocalisation in the triplet excited states of linear porphyrin oligomers.
Publisher: Springer Science and Business Media LLC
Date: 22-03-2017
DOI: 10.1038/NCOMMS14842
Abstract: The exchange interaction, J , between two spin centres is a convenient measure of through bond electronic communication. Here, we investigate quantum interference phenomena in a bis-copper six-porphyrin nanoring by electron paramagnetic resonance spectroscopy via measurement of the exchange coupling between the copper centres. Using an analytical expression accounting for both dipolar and exchange coupling to simulate the time traces obtained in a double electron electron resonance experiment, we demonstrate that J can be quantified to high precision even in the presence of significant through-space coupling. We show that the exchange coupling between two spin centres is increased by a factor of 4.5 in the ring structure with two parallel coupling paths as compared to an otherwise identical system with just one coupling path, which is a clear signature of constructive quantum interference.
Publisher: American Chemical Society (ACS)
Date: 19-06-2015
DOI: 10.1021/JACS.5B04511
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B907010A
Abstract: Double electron-electron resonance (DEER) spectroscopy can determine, from measurement of the dipolar interaction, the distance and orientation between two paramagnetic centres in systems lacking long-range order such as powders or frozen solution s les. In spin systems with considerable anisotropy, the microwave pulses excite only a fraction of the electron paramagnetic resonance (EPR) spectrum and the resulting orientation selection needs to be explicitly taken into account if a meaningful distance and orientation is to be determined. Here, a general method is presented to analyze the dipolar interaction between two paramagnetic spin centres from a series of DEER traces recorded so that different orientations of the spin-spin vector are s led. Delocalised spin density distributions and spin projection factors (as for ex le in iron-sulfur clusters), are explicitly included. Application of the analysis to a spin-labelled flavoprotein reductase/reduced iron-sulfur ferredoxin protein complex and a bi-radical with two Cu(ii) ions provides distance and orientation information between the radical centres. In the protein complex this enables the protein-protein binding geometry to be defined. Experimentally, orientationally selective DEER measurements are possible on paramagnetic systems where the resonator bandwidth allows the frequencies of pump and detection pulses to be separated sufficiently to excite enough orientations to define adequately the spin-spin vector.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP07424J
Abstract: Excitation wavelength-dependent EPR and ENDOR reveal localization of the triplet state in twisted conformations of porphyrin oligomers.
Publisher: Springer Berlin Heidelberg
Date: 2013
DOI: 10.1007/430_2013_115
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CP24112A
Abstract: Palustrisredoxin-B (PuxB) from Rhodopseudomonas palustris (CGA009) is a [2Fe-2S] ferredoxin which is able to accept electrons from NADH via the flavin-dependent palustrisredoxin reductase (PuR) these electrons can then be transferred to the P450 enzyme (CYP199A2). This work reports on the paramagnetic state of the [2Fe-2S](+) cluster in PuxB, both alone and in the PuR-PuxB complex. Aided by the X-ray crystal structure of PuxB, the protons nearest to the reduced [2Fe-2S](+) cluster were used as magnetic probes to quantify the g-matrix orientation and anisotropic magnetic moment of the paramagnetic centre. (1)H hyperfine couplings were measured with W-band Davies ENDOR and X-band HYSCORE spectroscopy and fitted to a model in which (1)H dipolar couplings were calculated assuming point magnetic moments located at the Fe ions, and bridging and coordinating cysteine sulfur atoms. The absolute sign of a (1)H hyperfine coupling was measured using a variable mixing time ENDOR experiment to confirm the assignment of the Fe(3+) and Fe(2+) ions. For the anti-ferromagnetically coupled cluster the magnetic moment is described in terms of spin projection factors, and our analysis yields values of K(exp)(A) = +2.33 to +1.85 (ferric site), and K(exp)(B) = -1.33 to -0.85 (ferrous site). These values are discussed in terms of the delocalisation of the spin density and hence the limitations of applying a local site spin coupling model to calculate the spin projection factors in a complex with considerable overlap of the α- and β-spin magnetic oribitals. The accurate description of the g-matrix orientation and magnetic moment of this [2Fe-2S](+) cluster enable it to be utilised as a paramagnetic spin probe, for ex le, to measure electron-electron distances. In the pdb reference frame of PuxB (code ) the g(∥) axis vector is g(∥) = [-0.6524 ± 0.0248, -0.6269 ± 0.0115, 0.4259 ± 0.0405], with the principal g-values of g(⊥) = 1.9328 ± 0.0003, g(∥) = 2.0233 ± 0.0003.
Publisher: Proceedings of the National Academy of Sciences
Date: 07-03-2013
Abstract: The twin-arginine transport system (Tat) has the remarkable ability of transporting folded proteins across membranes while avoiding uncontrolled ion leakage. Tat is essential for plant photosynthesis and is required for bacterial pathogenesis. The mechanism by which folded proteins are translocated is poorly understood. We have determined the structure of the TatA oligomer, which is responsible for the translocation step, and evaluated its impact on lipid bilayers. The results suggest a mechanism of protein translocation involving thinning and perturbing the membrane bilayer. The approach used here will be useful for structural analysis of other oligomeric proteins that weakly assemble in the membrane.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Christiane Timmel.