MoK- andL-edge X-ray absorption spectroscopic study of the ADP·AlF4−-stabilized nitrogenase complex: comparison with MoFe protein in solution and single crystal

Corbett, Mary C.; Tezcan, F.A.; Einsle, Oliver; Walton, Mika Y.; Rees, Douglas C.; Latimer, Matthew J.; Hedman, Britt

doi:10.1107/s0909049504027827

Cited by 16 publications

(15 citation statements)

References 33 publications

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“…In addition, the L 2,3 -edge spectra contain d -splitting information that can be rationalized theoretically, using, for example TT-multiplet calculations, to yield chemically useful information such as ligand field, site symmetry, spin-state and covalency. Hence, it is not surprising that several Mo L-edge studies are present in the literature (for example: [10-12, 27]). Finally, for paramagnetic compounds, L 2,3 -edges in general are known to exhibit a large x-ray magnetic circular dichroism which can probe magnetic properties of the Mo center [9].…”

Section: Discussionmentioning

confidence: 99%

“…By contrast, the Mo L 2 and L 3 -edges, which occur around 2626.0 eV and 2523.2 respectively, comprise dipole allowed 2p → 4d transitions. These have been measured for a number of systems including selected Mo enzyme systems [10, 11] and related model compounds (for example, [12]) and they have been shown to be sensitive to the ligand field about the Mo as well as the Mo oxidation state.…”

Section: Introductionmentioning

confidence: 99%

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Molybdenum X-ray absorption edges from 200 to 20,000eV: The benefits of soft X-ray spectroscopy for chemical speciation

George

Drury

et al. 2009

Journal of Inorganic Biochemistry

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We have surveyed the chemical utility of the near-edge structure of molybdenum x-ray absorption edges from the hard x-ray K-edge at 20,000 eV down to the soft x-ray M 4,5 -edges at ~230 eV. We compared, for each edge, the spectra of two tetrahedral anions, MoO 4 and MoS 4 2-. We used three criteria for assessing near-edge structure of each edge: (i) the ratio of the observed chemical shift between MoO 4 2-and MoS 4 2-and the linewidth, (ii) the chemical information from analysis of the near-edge structure and (iii) the ease of measurement using fluorescence detection. Not surprisingly, the K-edge was by far the easiest to measure, but it contained the least information. The L 2,3 -edges, although harder to measure, had benefits with regard to selection rules and chemical speciation in that they had both a greater chemical shift as well as detailed lineshapes which could be theoretically analyzed in terms of Mo ligand field, symmetry, and covalency. The soft x-ray M 2,3 -edges were perhaps the least useful, in that they were difficult to measure using fluorescence detection and had very similar information content to the corresponding L 2,3 -edges.Interestingly, the soft x-ray, low energy (~230 eV) M 4,5 -edges had greatest potential chemical sensitivity and using our high resolution superconducting tunnel junction (STJ) fluorescence detector they appear to be straightforward to measure. The spectra were amenable to analysis using both the TT-multiplet approach and FEFF. The results using FEFF indicate that the sharp near-edge peaks arise from 3d → 5p transitions, while the broad edge structure has predominately 3d → 4f character. A proper understanding of the dependence of these soft x-ray spectra on ligand field and site geometry is necessary before a complete assessment of the utility of the Mo M 4,5 -* Corresponding author: sjgeorge@lbl.gov, +1 510 486 6094, FAX +1 510 486 5664. Supporting Information(1) Crystallographic data of Na 2 MoS 4 in CIF format.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Molybdenum X-ray absorption edges from 200 to 20,000eV: The benefits of soft X-ray spectroscopy for chemical speciation

George

Drury

et al. 2009

Journal of Inorganic Biochemistry

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“…Unfortunately, it is not always straightforward to correlate structural results from EXAFS with those from crystallography because the resolutions of crystallographic experiments are usually lower than that of the EXAFS experiment and because there may be differences between the two structures analyzed, in addition to damage or reduction effects, that are a consequence of differences between the protein in solution and in a crystal (Dodd et al, 2000). The recently developed instrumentation for single-crystal XAS at SSRL (Latimer et al, 2005), which enables the XAS measurement of protein crystals under conditions similar to those of a typical crystallography experiment (Yano et al, 2005;Corbett et al, 2005), provides the perfect path for assessing the factors that influence X-ray damage of metalloproteins. Described herein is the use of the single-crystal instrumentation for the study of the impact of temperature on the dose-dependent photoreduction of the metalloprotein putidaredoxin (Pdx), a $12 kDa [Fe 2 S 2 ]-cluster-containing protein that is the specific reductant and effector of cytochrome P450 during camphor hydroxylation.…”

Section: Introductionmentioning

confidence: 99%

Photoreduction of the active site of the metalloprotein putidaredoxin by synchrotron radiation

Corbett¹,

Latimer²,

Poulos³

et al. 2007

Acta Crystallogr D Biol Cryst

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103

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X-ray damage to protein crystals is often assessed on the basis of the degradation of diffraction intensity, yet this measure is not sensitive to the rapid changes that occur at photosensitive groups such as the active sites of metalloproteins. Here, X-ray absorption spectroscopy is used to study the X-ray dose-dependent photoreduction of crystals of the [Fe(2)S(2)]-containing metalloprotein putidaredoxin. A dramatic decrease in the rate of photoreduction is observed in crystals cryocooled with liquid helium at 40 K compared with those cooled with liquid nitrogen at 110 K. Whereas structural changes consistent with cluster reduction occur in the active site of the crystal measured at 110 K, no such changes occur in the crystal measured at 40 K, even after an eightfold increase in dose. When the structural results from extended X-ray absorption fine-structure measurements are compared with those obtained by crystallography on this and similar proteins, it is apparent that X-ray-induced photoreduction has had an impact on the crystallographic data and subsequent structure solutions. These results strongly indicate the importance of using liquid-helium-based cooling for metalloprotein crystallography in order to avoid the subtle yet important changes that can take place at the metalloprotein active sites when liquid-nitrogen-based cooling is used. The study also illustrates the need for direct measurement of the redox states of the metals, through X-ray absorption spectroscopy, simultaneously with the crystallographic measurements.

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“…In the past decade, typical values of k max for metalloproteins studies were research papers between 11 and 14 Å À1 . Recent experiments (Rich et al, 1998;Corbett et al, 2005Corbett et al, , 2006 on appropriate samples push this limit up to 16-18 Å À1 . With the optimization of experimental set-ups (sensitive detectors and more stable sources and optics) allowing lower noise in the data, the k max value may be increased up to 25 Å À1 as for human sulfite oxidase .…”

Section: Data Collection: Advances In Beamlines For Bioxasmentioning

confidence: 94%

Biological X-ray absorption spectroscopy and metalloproteomics

Ascone

Strange

2009

J Synchrotron Rad

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In the past seven years the size of the known protein sequence universe has been rapidly expanding. At present, more then five million entries are included in the UniProtKB/TrEMBL protein database. In this context, a retrospective evaluation of recent X-ray absorption studies is undertaken to assess its potential role in metalloproteomics. Metalloproteomics is the structural and functional characterization of metal-binding proteins. This is a new area of active research which has particular relevance to biology and for which X-ray absorption spectroscopy is ideally suited. In the last three years, biological X-ray absorption spectroscopy (BioXAS) has been included among the techniques used in post-genomics initiatives for metalloprotein characterization. The emphasis of this review is on the progress in BioXAS that has emerged from recent meetings in 2007-2008. Developments required to enable BioXAS studies to better contribute to metalloproteomics throughput are also discussed. Overall, this paper suggests that X-ray absorption spectroscopy could have a higher impact on metalloproteomics, contributing significantly to the understanding of metal site structures and of reaction mechanisms for metalloproteins.

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MoK- andL-edge X-ray absorption spectroscopic study of the ADP·AlF₄⁻-stabilized nitrogenase complex: comparison with MoFe protein in solution and single crystal

Cited by 16 publications

References 33 publications

Molybdenum X-ray absorption edges from 200 to 20,000eV: The benefits of soft X-ray spectroscopy for chemical speciation

Molybdenum X-ray absorption edges from 200 to 20,000eV: The benefits of soft X-ray spectroscopy for chemical speciation

Photoreduction of the active site of the metalloprotein putidaredoxin by synchrotron radiation

Biological X-ray absorption spectroscopy and metalloproteomics

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