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Title: Determination of the Complete Spin Density Distribution in 13 C-Labeled Protein-Bound Radical Intermediates Using Advanced 2D Electron Paramagnetic Resonance Spectroscopy and Density Functional Theory

Abstract

Determining the complete electron spin density distribution for protein-bound radicals, even with advanced pulsed electron paramagnetic resonance (EPR) methods, is a formidable task. Here we present a strategy to overcome this problem combining multifrequency HYSCORE and ENDOR measurements on site-specifically 13C-labeled samples with DFT calculations on model systems. As a demonstration of this approach, pulsed EPR experiments are performed on the primary Q A and secondary Q B ubisemiquinones of the photosynthetic reaction center from Rhodobacter sphaeroides 13C-labeled at the ring and tail positions. Despite the large number of nuclei interacting with the unpaired electron in these samples, two-dimensional X- and Q-band HYSCORE and orientation selective Q-band ENDOR resolve and allow for a characterization of the eight expected 13C resonances from significantly different hyperfine tensors for both semiquinones. From these results we construct, for the first time, the most complete experimentally determined maps of the s- and p π-orbital spin density distributions for any protein organic cofactor radical to date. This work lays a foundation for understanding the relationship between the electronic structure of semiquinones and their functional properties, and introduces new techniques for mapping out the spin density distribution that are readily applicable to other systems.

Authors:
ORCiD logo [1];  [2];  [3];  [4]
  1. Center for Biophysics and Computational Biology, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States, Department of Veterinary Clinical Medicine, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
  2. School of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.
  3. Center for Biophysics and Computational Biology, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States, Department of Biochemistry, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
  4. Department of Veterinary Clinical Medicine, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
Publication Date:
Research Org.:
Univ. of Illinois at Urbana−Champaign, Urbana, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1406160
Alternate Identifier(s):
OSTI ID: 1508078
Grant/Contract Number:  
[FG02-08ER15960]
Resource Type:
Published Article
Journal Name:
Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry
Additional Journal Information:
[Journal Name: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry Journal Volume: 121 Journal Issue: 44]; Journal ID: ISSN 1520-6106
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Taguchi, Alexander T., O’Malley, Patrick J., Wraight, Colin A., and Dikanov, Sergei A. Determination of the Complete Spin Density Distribution in 13 C-Labeled Protein-Bound Radical Intermediates Using Advanced 2D Electron Paramagnetic Resonance Spectroscopy and Density Functional Theory. United States: N. p., 2017. Web. doi:10.1021/acs.jpcb.7b10036.
Taguchi, Alexander T., O’Malley, Patrick J., Wraight, Colin A., & Dikanov, Sergei A. Determination of the Complete Spin Density Distribution in 13 C-Labeled Protein-Bound Radical Intermediates Using Advanced 2D Electron Paramagnetic Resonance Spectroscopy and Density Functional Theory. United States. doi:10.1021/acs.jpcb.7b10036.
Taguchi, Alexander T., O’Malley, Patrick J., Wraight, Colin A., and Dikanov, Sergei A. Wed . "Determination of the Complete Spin Density Distribution in 13 C-Labeled Protein-Bound Radical Intermediates Using Advanced 2D Electron Paramagnetic Resonance Spectroscopy and Density Functional Theory". United States. doi:10.1021/acs.jpcb.7b10036.
@article{osti_1406160,
title = {Determination of the Complete Spin Density Distribution in 13 C-Labeled Protein-Bound Radical Intermediates Using Advanced 2D Electron Paramagnetic Resonance Spectroscopy and Density Functional Theory},
author = {Taguchi, Alexander T. and O’Malley, Patrick J. and Wraight, Colin A. and Dikanov, Sergei A.},
abstractNote = {Determining the complete electron spin density distribution for protein-bound radicals, even with advanced pulsed electron paramagnetic resonance (EPR) methods, is a formidable task. Here we present a strategy to overcome this problem combining multifrequency HYSCORE and ENDOR measurements on site-specifically 13C-labeled samples with DFT calculations on model systems. As a demonstration of this approach, pulsed EPR experiments are performed on the primary QA and secondary QB ubisemiquinones of the photosynthetic reaction center from Rhodobacter sphaeroides 13C-labeled at the ring and tail positions. Despite the large number of nuclei interacting with the unpaired electron in these samples, two-dimensional X- and Q-band HYSCORE and orientation selective Q-band ENDOR resolve and allow for a characterization of the eight expected 13C resonances from significantly different hyperfine tensors for both semiquinones. From these results we construct, for the first time, the most complete experimentally determined maps of the s- and pπ-orbital spin density distributions for any protein organic cofactor radical to date. This work lays a foundation for understanding the relationship between the electronic structure of semiquinones and their functional properties, and introduces new techniques for mapping out the spin density distribution that are readily applicable to other systems.},
doi = {10.1021/acs.jpcb.7b10036},
journal = {Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry},
number = [44],
volume = [121],
place = {United States},
year = {2017},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1021/acs.jpcb.7b10036

Citation Metrics:
Cited by: 2 works
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Figures / Tables:

Figure 1 Figure 1: Symmetric locations of the QA and QB sites about the nonheme iron (green) in pdb entry 1DV3. The quinone ring carbons are numbered as referenced in the text, and only the first (CH2) and second (CH) carbons of the isoprenoid tails are shown extending from the C6 position.more » Differences in the number and strengths of the hydrogen bonds between the semiquinones and their surrounding residues give rise to unique spin density distributions for SQA and SQB.« less

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.