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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">The Semiquinone-Iron Complex of Photosystem II: Structural Insights from ESR and Theoretical Simulation; Evidence that the Native Ligand to the Non-Heme Iron Is Carbonate</title><author><name sortKey="Cox, Nicholas" sort="Cox, Nicholas" uniqKey="Cox N" first="Nicholas" last="Cox">Nicholas Cox</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Jin, Lu" sort="Jin, Lu" uniqKey="Jin L" first="Lu" last="Jin">Lu Jin</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Jaszewski, Adrian" sort="Jaszewski, Adrian" uniqKey="Jaszewski A" first="Adrian" last="Jaszewski">Adrian Jaszewski</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Smith, Paul J" sort="Smith, Paul J" uniqKey="Smith P" first="Paul J." last="Smith">Paul J. Smith</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Krausz, Elmars" sort="Krausz, Elmars" uniqKey="Krausz E" first="Elmars" last="Krausz">Elmars Krausz</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Rutherford, A William" sort="Rutherford, A William" uniqKey="Rutherford A" first="A. William" last="Rutherford">A. William Rutherford</name><affiliation><nlm:aff id="aff2"></nlm:aff></affiliation></author><author><name sortKey="Pace, Ron" sort="Pace, Ron" uniqKey="Pace R" first="Ron" last="Pace">Ron Pace</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">19804734</idno><idno type="pmc">2756360</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2756360</idno><idno type="RBID">PMC:2756360</idno><idno type="doi">10.1016/j.bpj.2009.06.033</idno><date when="2009">2009</date><idno type="wicri:Area/Pmc/Corpus">001787</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">001787</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">The Semiquinone-Iron Complex of Photosystem II: Structural Insights from ESR and Theoretical Simulation; Evidence that the Native Ligand to the Non-Heme Iron Is Carbonate</title><author><name sortKey="Cox, Nicholas" sort="Cox, Nicholas" uniqKey="Cox N" first="Nicholas" last="Cox">Nicholas Cox</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Jin, Lu" sort="Jin, Lu" uniqKey="Jin L" first="Lu" last="Jin">Lu Jin</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Jaszewski, Adrian" sort="Jaszewski, Adrian" uniqKey="Jaszewski A" first="Adrian" last="Jaszewski">Adrian Jaszewski</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Smith, Paul J" sort="Smith, Paul J" uniqKey="Smith P" first="Paul J." last="Smith">Paul J. Smith</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Krausz, Elmars" sort="Krausz, Elmars" uniqKey="Krausz E" first="Elmars" last="Krausz">Elmars Krausz</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author><author><name sortKey="Rutherford, A William" sort="Rutherford, A William" uniqKey="Rutherford A" first="A. William" last="Rutherford">A. William Rutherford</name><affiliation><nlm:aff id="aff2"></nlm:aff></affiliation></author><author><name sortKey="Pace, Ron" sort="Pace, Ron" uniqKey="Pace R" first="Ron" last="Pace">Ron Pace</name><affiliation><nlm:aff id="aff1"></nlm:aff></affiliation></author></analytic><series><title level="j">Biophysical Journal</title><idno type="ISSN">0006-3495</idno><idno type="eISSN">1542-0086</idno><imprint><date when="2009">2009</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><title>Abstract</title><p>The semiquinone-iron complex of photosystem II was studied using electron spin resonance (ESR) spectroscopy and density functional theory calculations. Two forms of the signal were investigated: 1), the native <italic>g</italic> ∼ 1.9 form; and 2), the <italic>g</italic> ∼ 1.84 form, which is well known in purple bacterial reaction centers and occurs in photosystem II when treated with formate. The <italic>g</italic> ∼ 1.9 form shows low- and high-field edges at <italic>g</italic> ∼ 3.5 and <italic>g</italic> < 0.8, respectively, and resembles the <italic>g</italic> ∼ 1.84 form in terms of shape and width. Both types of ESR signal were simulated using the theoretical approach used previously for the BRC complex, a spin Hamiltonian formalism in which the semiquinone radical magnetically interacts (<italic>J</italic> ∼ 1 cm<sup>−1</sup>) with the nearby high-spin Fe<sup>2+</sup>. The two forms of ESR signal differ mainly by an axis rotation of the exchange coupling tensor (<italic>J</italic>) relative to the zero-field tensor (<italic>D</italic>) and a small increase in the zero-field parameter <italic>D</italic> (∼6 cm<sup>−1</sup>). Density functional theory calculations were conducted on model semiquinone-iron systems to identify the physical nature of these changes. The replacement of formate (or glutamate in the bacterial reaction centers) by bicarbonate did not result in changes in the coupling environment. However, when carbonate (CO<sub>3</sub><sup>2−</sup>) was used instead of bicarbonate, the exchange and zero-field tensors did show changes that matched those obtained from the spectral simulations. This indicates that 1), the doubly charged carbonate ion is responsible for the <italic>g</italic> ∼ 1.9 form of the semiquinone-iron signal; and 2), carbonate, rather than bicarbonate, is the ligand to the iron.</p></div></front></TEI><pmc article-type="research-article"><pmc-comment>The publisher of this article does not allow downloading of the full text in XML form.</pmc-comment>
<front><journal-meta><journal-id journal-id-type="nlm-ta">Biophys J</journal-id><journal-title>Biophysical Journal</journal-title><issn pub-type="ppub">0006-3495</issn><issn pub-type="epub">1542-0086</issn><publisher><publisher-name>The Biophysical Society</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="pmid">19804734</article-id><article-id pub-id-type="pmc">2756360</article-id><article-id pub-id-type="publisher-id">BPJ914</article-id><article-id pub-id-type="doi">10.1016/j.bpj.2009.06.033</article-id><article-categories><subj-group subj-group-type="heading"><subject>Protein</subject></subj-group></article-categories><title-group><article-title>The Semiquinone-Iron Complex of Photosystem II: Structural Insights from ESR and Theoretical Simulation; Evidence that the Native Ligand to the Non-Heme Iron Is Carbonate</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Cox</surname><given-names>Nicholas</given-names></name><email>cox@mpi-muelheim.mpg.de</email><xref rid="aff1" ref-type="aff">†</xref><xref rid="cor1" ref-type="corresp">∗</xref></contrib><contrib contrib-type="author"><name><surname>Jin</surname><given-names>Lu</given-names></name><xref rid="aff1" ref-type="aff">†</xref></contrib><contrib contrib-type="author"><name><surname>Jaszewski</surname><given-names>Adrian</given-names></name><xref rid="aff1" ref-type="aff">†</xref></contrib><contrib contrib-type="author"><name><surname>Smith</surname><given-names>Paul J.</given-names></name><xref rid="aff1" ref-type="aff">†</xref></contrib><contrib contrib-type="author"><name><surname>Krausz</surname><given-names>Elmars</given-names></name><xref rid="aff1" ref-type="aff">†</xref></contrib><contrib contrib-type="author"><name><surname>Rutherford</surname><given-names>A. William</given-names></name><xref rid="aff2" ref-type="aff">‡</xref></contrib><contrib contrib-type="author"><name><surname>Pace</surname><given-names>Ron</given-names></name><xref rid="aff1" ref-type="aff">†</xref></contrib></contrib-group><aff id="aff1"><addr-line><sup>†</sup>Research School of Chemistry, Australian National University, Canberra, Australia</addr-line></aff><aff id="aff2"><addr-line><sup>‡</sup>iBiTec-S, Centre National de la Recherche Scientifiques, Centre d'Études Atomiques Saclay, Gif-sur-Yvette, France</addr-line></aff><author-notes><corresp id="cor1"><label>∗</label>Corresponding author <email>cox@mpi-muelheim.mpg.de</email></corresp></author-notes><pub-date pub-type="ppub"><day>07</day><month>10</month><year>2009</year></pub-date><volume>97</volume><issue>7</issue><fpage>2024</fpage><lpage>2033</lpage><history><date date-type="received"><day>6</day><month>2</month><year>2009</year></date><date date-type="accepted"><day>24</day><month>6</month><year>2009</year></date></history><permissions><copyright-statement>© 2009 by the Biophysical Society..</copyright-statement><copyright-year>2009</copyright-year><copyright-holder>Biophysical Society</copyright-holder><license><p>This document may be redistributed and reused, subject to <ext-link ext-link-type="uri" xlink:href="http://www.elsevier.com/wps/find/authorsview.authors/supplementalterms1.0">certain conditions</ext-link>.</p></license></permissions><abstract><title>Abstract</title><p>The semiquinone-iron complex of photosystem II was studied using electron spin resonance (ESR) spectroscopy and density functional theory calculations. Two forms of the signal were investigated: 1), the native <italic>g</italic> ∼ 1.9 form; and 2), the <italic>g</italic> ∼ 1.84 form, which is well known in purple bacterial reaction centers and occurs in photosystem II when treated with formate. The <italic>g</italic> ∼ 1.9 form shows low- and high-field edges at <italic>g</italic> ∼ 3.5 and <italic>g</italic> < 0.8, respectively, and resembles the <italic>g</italic> ∼ 1.84 form in terms of shape and width. Both types of ESR signal were simulated using the theoretical approach used previously for the BRC complex, a spin Hamiltonian formalism in which the semiquinone radical magnetically interacts (<italic>J</italic> ∼ 1 cm<sup>−1</sup>) with the nearby high-spin Fe<sup>2+</sup>. The two forms of ESR signal differ mainly by an axis rotation of the exchange coupling tensor (<italic>J</italic>) relative to the zero-field tensor (<italic>D</italic>) and a small increase in the zero-field parameter <italic>D</italic> (∼6 cm<sup>−1</sup>). Density functional theory calculations were conducted on model semiquinone-iron systems to identify the physical nature of these changes. The replacement of formate (or glutamate in the bacterial reaction centers) by bicarbonate did not result in changes in the coupling environment. However, when carbonate (CO<sub>3</sub><sup>2−</sup>) was used instead of bicarbonate, the exchange and zero-field tensors did show changes that matched those obtained from the spectral simulations. This indicates that 1), the doubly charged carbonate ion is responsible for the <italic>g</italic> ∼ 1.9 form of the semiquinone-iron signal; and 2), carbonate, rather than bicarbonate, is the ligand to the iron.</p></abstract></article-meta></front><floats-wrap><fig id="fig1"><label>Figure 1</label><caption><p>Derivative ESR spectra of the semiquinone-iron observed in PS II. (<italic>A</italic>) <italic>g</italic> ∼ 1.84 Q<sub>A</sub><sup>−</sup>-Fe<sup>2+</sup> signal (5 K) seen in formate-treated PS II (similar to BRC (<xref rid="bib28" ref-type="bibr">28</xref>)). (<italic>B</italic>) <italic>g</italic> ∼ 1.9 Q<sub>A</sub><sup>−</sup>-Fe<sup>2+</sup> signal (5 K) seen in bicarbonate-treated PS II. (<italic>C</italic>) <italic>g</italic> ∼ 1.9 Q<sub>A</sub><sup>−</sup>-Fe<sup>2+</sup> signal (15 K) seen in bicarbonate-treated PS II.</p></caption><graphic xlink:href="gr1"></graphic></fig><fig id="fig2"><label>Figure 2</label><caption><p>Absorption ESR spectra of the <italic>g</italic> ∼ 1.9 semiquinone-iron signal observed in PS II at 5 K (<italic>black trace</italic>) and 15 K (<italic>gray trace</italic>). Spectra scaled to account for Curie temperature dependence (i.e., 15 K spectrum × 3). The radical region around <italic>g</italic> = 2 (<italic>gray column</italic>) is dominated by light-induced radicals (D<sup>+</sup>) and has been omitted for clarity.</p></caption><graphic xlink:href="gr2"></graphic></fig><fig id="fig3"><label>Figure 3</label><caption><p>Simulation of the semiquinone-iron using the spin Hamiltonian formalism: comparison of experimental and theoretical results. Parameter values are as in <xref rid="tbl1" ref-type="table">Table 1</xref>. (<italic>A</italic>) <italic>g</italic> ∼ 1.84 (BRC + o-phenanthroline, taken from Butler et al. (<xref rid="bib28" ref-type="bibr">28</xref>)). (<italic>B</italic>) <italic>g</italic> ∼ 1.9 (PS II) at 5 K. (<italic>C</italic>) <italic>g</italic> ∼ 1.9 (PS II) at 15 K. Free radical region omitted in <italic>B</italic> and <italic>C</italic>. <italic>Black lines</italic>, total simulation; <italic>gray lines</italic>, doublet transitions.</p></caption><graphic xlink:href="gr3"></graphic></fig><fig id="fig4"><label>Figure 4</label><caption><p>Orientation of the Fe<sup>2+</sup> hyperfine tensor for the semiquinone-iron geometry seen in BRC/ PS II. (<italic>A</italic>) Hyperfine tensors are color-coded green for BRC + glutamate; blue for BRC + formate; orange for PS II + formate; red for PS II + bicarbonate; and pink for PS II + carbonate. (<italic>B</italic>) A simple representation of the rotation of the hyperfine tensor in the various ligand systems.</p></caption><graphic xlink:href="gr4"></graphic></fig><fig id="fig5"><label>Figure 5</label><caption><p>The quinone-iron complex of PS II. Residues in the immediate vicinity of the carbonate ligand to the non-heme iron (Loll et al. (<xref rid="bib14" ref-type="bibr">14</xref>)).</p></caption><graphic xlink:href="gr5"></graphic></fig><fig id="sc1"><label>Scheme 1</label><caption><p>Acceptor-side electron transfer pathways in PS II and BRC: the two-electron gate (<xref rid="bib2" ref-type="bibr">2</xref>).</p></caption><graphic xlink:href="sc1"></graphic></fig><table-wrap position="float" id="tbl1"><label>Table 1</label><caption><p>Optimized parameter set for simulation of semiquinone-iron signals</p></caption><table frame="hsides" rules="groups"><thead><tr><th></th><th><italic>g</italic> ∼ 1.84 (K, BRC) (<xref rid="bib28" ref-type="bibr">28</xref>)</th><th><italic>g</italic> ∼ 1.9 (K, PS II)<xref rid="tblfn1" ref-type="table-fn">∗</xref></th></tr></thead><tbody><tr><td><italic>J<sub>x</sub></italic></td><td align="char">−0.13</td><td align="char">−0.90</td></tr><tr><td><italic>J<sub>y</sub></italic></td><td align="char">−0.58</td><td align="char">−0.50</td></tr><tr><td><italic>J<sub>z</sub></italic></td><td align="char">−0.58</td><td align="char">−0.10</td></tr><tr><td><italic>J</italic><sub>ISO</sub><xref rid="tblfn1" ref-type="table-fn">∗</xref></td><td align="char">−0.43</td><td align="char">−0.52</td></tr><tr><td>D</td><td align="char">7.6</td><td align="char">15.0</td></tr><tr><td>E/D</td><td align="char">0.25</td><td align="char">0.27</td></tr><tr><td>Width (FWHM)</td><td>160 (G)</td><td>600 (G)</td></tr></tbody></table><table-wrap-foot><fn><p>Semiquinone-iron signals used are those shown in <xref rid="fig3" ref-type="fig">Fig. 3</xref>.</p></fn></table-wrap-foot><table-wrap-foot><fn id="tblfn1"><label>∗</label><p><italic>g</italic><sub>Fe</sub> tensor values are as in Butler et al. (<xref rid="bib28" ref-type="bibr">28</xref>).</p></fn></table-wrap-foot></table-wrap><table-wrap position="float" id="tbl2"><label>Table 2</label><caption><p>DFT estimates of the exchange coupling, hyperfine, and zero-field tensors of the semiquinone and the Fe<sup>2+</sup> center</p></caption><table frame="hsides" rules="groups"><thead><tr><th rowspan="2"></th><th rowspan="2">S<sup>2</sup><sub>HS</sub></th><th rowspan="2">S<sup>2</sup><sub>LS</sub></th><th rowspan="2">E<sub>HS</sub> (cm<sup>−1</sup>)</th><th rowspan="2">E<sub>LS</sub> (cm<sup>−1</sup>)</th><th rowspan="2">J<sub>ISO</sub> (cm<sup>−1</sup>)</th><th colspan="3">Fe<sup>2+</sup> hyperfine (10<sup>−4</sup> cm<sup>−1</sup>)<hr></hr></th><th colspan="2">Zero-field parameters<hr></hr></th></tr><tr><th><italic>x</italic></th><th><italic>y</italic></th><th><italic>z</italic></th><th><italic>D</italic> (cm<sup>−1</sup>)</th><th><italic>E</italic>/<italic>D</italic></th></tr></thead><tbody><tr><td>BRC + glutamate<xref rid="tblfn2" ref-type="table-fn">∗</xref></td><td align="char">8.75</td><td align="char">3.78</td><td align="char">−806599620</td><td align="char">−806599622</td><td align="char">−0.34</td><td align="char">−9.1</td><td align="char">14.4</td><td align="char">−5.3</td><td align="char">−3.0 (5.3)</td><td align="char">0.22</td></tr><tr><td>BRC + formate<xref rid="tblfn2" ref-type="table-fn">∗</xref></td><td align="char">8.75</td><td align="char">3.78</td><td align="char">−780708648</td><td align="char">−780708650</td><td align="char">−0.37</td><td align="char">−9.2</td><td align="char">14.4</td><td align="char">−5.2</td><td align="char">−3.2 (5.5)</td><td align="char">0.20</td></tr><tr><td>PS II + formate<xref rid="tblfn2" ref-type="table-fn">∗</xref></td><td align="char">8.75</td><td align="char">3.78</td><td align="char">−755589365</td><td align="char">−755589369</td><td align="char">−0.70</td><td align="char">−9.5</td><td align="char">14.1</td><td align="char">−4.5</td><td align="char">−3.1 (5.4)</td><td align="char">0.24</td></tr><tr><td>PS II + bicarbonate<xref rid="tblfn2" ref-type="table-fn">∗</xref></td><td align="char">8.75</td><td align="char">3.80</td><td align="char">−755465371</td><td align="char">−755465374</td><td align="char">−0.70</td><td align="char">−8.9</td><td align="char">14.2</td><td align="char">−5.3</td><td align="char">−2.9 (5.2)</td><td align="char">0.21</td></tr><tr><td>PS II + carbonate<xref rid="tblfn2" ref-type="table-fn">∗</xref></td><td align="char">8.75</td><td align="char">3.78</td><td align="char">−739070237</td><td align="char">−739070240</td><td align="char">−0.43</td><td align="char">−5.1</td><td align="char">13.0</td><td align="char">−8.0</td><td align="char">3.0 (11.3)</td><td align="char">0.28</td></tr><tr><td>PS II + carbonate<xref rid="tblfn3" ref-type="table-fn">†</xref></td><td align="char">8.75</td><td align="char">3.78</td><td align="char">−739070237</td><td align="char">−739070240</td><td align="char">−0.43</td><td align="char">−5.1</td><td align="char">13.0</td><td align="char">−8.0</td><td>10.5</td><td align="char">0.28</td></tr></tbody></table><table-wrap-foot><fn><p>Numbers in parentheses (<italic>D</italic> values) are corrected assuming an offset of 8.3 cm<sup>−1</sup>.</p></fn></table-wrap-foot><table-wrap-foot><fn id="tblfn2"><label>∗</label><p>High spin (ferromagnetic coupling) (HS).</p></fn></table-wrap-foot><table-wrap-foot><fn id="tblfn3"><label>†</label><p>Low spin (antiferromagnetic coupling) (LS).</p></fn></table-wrap-foot></table-wrap></floats-wrap></pmc></record>Pour manipuler ce document sous Unix (Dilib)
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