Incorporation of 2,3-disubstituted-1,4-naphthoquinones into the A1 binding site of photosystem I studied by EPR and ENDOR spectroscopy

Art van der Est, Yulia Pushkar, Irina Karyagina, Branden Fonovic, Travis Dudding, Jens Niklas, Wolfgang Lubitz, John H. Golbeck

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Abstract

Transient electron paramagnetic resonance and pulsed electron-nuclear double resonance (ENDOR) spectra of the state P.+700A.-1 in photosystem I containing a series of non-native naphthoquinones (NQs) are presented. Previous studies have shown that quinones bind to the A1 site with only one of their carbonyl groups H-bonded to the protein and that the asymmetric H-bond produces an odd alternant distribution of the spin density within the quinone. It is known that the native phylloquinone binds with its methyl group meta and its phytyl tail ortho to the H-bonded carbonyl. Monosubstituted NQs with short alkyl chains have been found to bind preferentially with their alkyl side groups meta to the H-bonded carbonyl. The selectivity of the binding site toward methyl and short chain substituents is studied by incorporating disubstituted NQs that have a methyl group at the 2-position and a short chain at the 3-position of the quinone ring. The hyperfine couplings (hfcs) of the methyl group protons are sensitive to the spin density distribution on the quinone and are used to deduce the position of the methyl group relative to the H-bonded carbonyl. The measured methyl proton hfcs indicate that the disubstituted quinones bind exclusively with their methyl group in the meta position relative to the H-bonded carbonyl and no evidence for binding with the methyl group in the ortho position is found. The disubstituted quinones have also been chosen to study the effect of electron withdrawing substituents on the spin density distribution. When the short chain contains electronegative atoms such as sulfur or chlorine, the methyl proton hfcs of the quinone in the A1 binding site are found to be significantly larger than those of 2-methyl-1,4-naphthoquinone and phylloquinone in the same environment. Solution ENDOR measurements of the quinone radical anions in isopropanol and density functional theory (DFT) calculations in vacuo show that this increase in the hfcs is mostly intrinsic to the quinones due to the electron-withdrawing ability of the short chain and is not a result of differences in the binding to the protein. The DFT calculations suggest that the main reason for the increased methyl proton hfcs is delocalization of the singly occupied molecular orbital onto the side chain, which leads to an increase of the spin density on the neighboring carbon, which carries methyl group.

Original languageEnglish (US)
Pages (from-to)65-83
Number of pages19
JournalApplied Magnetic Resonance
Volume37
Issue number1
DOIs
StatePublished - Jan 1 2010

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quinones
spectroscopy
electrons
phylloquinone
protons
density distribution
density functional theory
proteins
chlorine
molecular orbitals
electron paramagnetic resonance
sulfur
selectivity
anions
carbon
rings

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics

Cite this

van der Est, Art ; Pushkar, Yulia ; Karyagina, Irina ; Fonovic, Branden ; Dudding, Travis ; Niklas, Jens ; Lubitz, Wolfgang ; Golbeck, John H. / Incorporation of 2,3-disubstituted-1,4-naphthoquinones into the A1 binding site of photosystem I studied by EPR and ENDOR spectroscopy. In: Applied Magnetic Resonance. 2010 ; Vol. 37, No. 1. pp. 65-83.
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title = "Incorporation of 2,3-disubstituted-1,4-naphthoquinones into the A1 binding site of photosystem I studied by EPR and ENDOR spectroscopy",
abstract = "Transient electron paramagnetic resonance and pulsed electron-nuclear double resonance (ENDOR) spectra of the state P.+700A.-1 in photosystem I containing a series of non-native naphthoquinones (NQs) are presented. Previous studies have shown that quinones bind to the A1 site with only one of their carbonyl groups H-bonded to the protein and that the asymmetric H-bond produces an odd alternant distribution of the spin density within the quinone. It is known that the native phylloquinone binds with its methyl group meta and its phytyl tail ortho to the H-bonded carbonyl. Monosubstituted NQs with short alkyl chains have been found to bind preferentially with their alkyl side groups meta to the H-bonded carbonyl. The selectivity of the binding site toward methyl and short chain substituents is studied by incorporating disubstituted NQs that have a methyl group at the 2-position and a short chain at the 3-position of the quinone ring. The hyperfine couplings (hfcs) of the methyl group protons are sensitive to the spin density distribution on the quinone and are used to deduce the position of the methyl group relative to the H-bonded carbonyl. The measured methyl proton hfcs indicate that the disubstituted quinones bind exclusively with their methyl group in the meta position relative to the H-bonded carbonyl and no evidence for binding with the methyl group in the ortho position is found. The disubstituted quinones have also been chosen to study the effect of electron withdrawing substituents on the spin density distribution. When the short chain contains electronegative atoms such as sulfur or chlorine, the methyl proton hfcs of the quinone in the A1 binding site are found to be significantly larger than those of 2-methyl-1,4-naphthoquinone and phylloquinone in the same environment. Solution ENDOR measurements of the quinone radical anions in isopropanol and density functional theory (DFT) calculations in vacuo show that this increase in the hfcs is mostly intrinsic to the quinones due to the electron-withdrawing ability of the short chain and is not a result of differences in the binding to the protein. The DFT calculations suggest that the main reason for the increased methyl proton hfcs is delocalization of the singly occupied molecular orbital onto the side chain, which leads to an increase of the spin density on the neighboring carbon, which carries methyl group.",
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Incorporation of 2,3-disubstituted-1,4-naphthoquinones into the A1 binding site of photosystem I studied by EPR and ENDOR spectroscopy. / van der Est, Art; Pushkar, Yulia; Karyagina, Irina; Fonovic, Branden; Dudding, Travis; Niklas, Jens; Lubitz, Wolfgang; Golbeck, John H.

In: Applied Magnetic Resonance, Vol. 37, No. 1, 01.01.2010, p. 65-83.

Research output: Contribution to journalArticle

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T1 - Incorporation of 2,3-disubstituted-1,4-naphthoquinones into the A1 binding site of photosystem I studied by EPR and ENDOR spectroscopy

AU - van der Est, Art

AU - Pushkar, Yulia

AU - Karyagina, Irina

AU - Fonovic, Branden

AU - Dudding, Travis

AU - Niklas, Jens

AU - Lubitz, Wolfgang

AU - Golbeck, John H.

PY - 2010/1/1

Y1 - 2010/1/1

N2 - Transient electron paramagnetic resonance and pulsed electron-nuclear double resonance (ENDOR) spectra of the state P.+700A.-1 in photosystem I containing a series of non-native naphthoquinones (NQs) are presented. Previous studies have shown that quinones bind to the A1 site with only one of their carbonyl groups H-bonded to the protein and that the asymmetric H-bond produces an odd alternant distribution of the spin density within the quinone. It is known that the native phylloquinone binds with its methyl group meta and its phytyl tail ortho to the H-bonded carbonyl. Monosubstituted NQs with short alkyl chains have been found to bind preferentially with their alkyl side groups meta to the H-bonded carbonyl. The selectivity of the binding site toward methyl and short chain substituents is studied by incorporating disubstituted NQs that have a methyl group at the 2-position and a short chain at the 3-position of the quinone ring. The hyperfine couplings (hfcs) of the methyl group protons are sensitive to the spin density distribution on the quinone and are used to deduce the position of the methyl group relative to the H-bonded carbonyl. The measured methyl proton hfcs indicate that the disubstituted quinones bind exclusively with their methyl group in the meta position relative to the H-bonded carbonyl and no evidence for binding with the methyl group in the ortho position is found. The disubstituted quinones have also been chosen to study the effect of electron withdrawing substituents on the spin density distribution. When the short chain contains electronegative atoms such as sulfur or chlorine, the methyl proton hfcs of the quinone in the A1 binding site are found to be significantly larger than those of 2-methyl-1,4-naphthoquinone and phylloquinone in the same environment. Solution ENDOR measurements of the quinone radical anions in isopropanol and density functional theory (DFT) calculations in vacuo show that this increase in the hfcs is mostly intrinsic to the quinones due to the electron-withdrawing ability of the short chain and is not a result of differences in the binding to the protein. The DFT calculations suggest that the main reason for the increased methyl proton hfcs is delocalization of the singly occupied molecular orbital onto the side chain, which leads to an increase of the spin density on the neighboring carbon, which carries methyl group.

AB - Transient electron paramagnetic resonance and pulsed electron-nuclear double resonance (ENDOR) spectra of the state P.+700A.-1 in photosystem I containing a series of non-native naphthoquinones (NQs) are presented. Previous studies have shown that quinones bind to the A1 site with only one of their carbonyl groups H-bonded to the protein and that the asymmetric H-bond produces an odd alternant distribution of the spin density within the quinone. It is known that the native phylloquinone binds with its methyl group meta and its phytyl tail ortho to the H-bonded carbonyl. Monosubstituted NQs with short alkyl chains have been found to bind preferentially with their alkyl side groups meta to the H-bonded carbonyl. The selectivity of the binding site toward methyl and short chain substituents is studied by incorporating disubstituted NQs that have a methyl group at the 2-position and a short chain at the 3-position of the quinone ring. The hyperfine couplings (hfcs) of the methyl group protons are sensitive to the spin density distribution on the quinone and are used to deduce the position of the methyl group relative to the H-bonded carbonyl. The measured methyl proton hfcs indicate that the disubstituted quinones bind exclusively with their methyl group in the meta position relative to the H-bonded carbonyl and no evidence for binding with the methyl group in the ortho position is found. The disubstituted quinones have also been chosen to study the effect of electron withdrawing substituents on the spin density distribution. When the short chain contains electronegative atoms such as sulfur or chlorine, the methyl proton hfcs of the quinone in the A1 binding site are found to be significantly larger than those of 2-methyl-1,4-naphthoquinone and phylloquinone in the same environment. Solution ENDOR measurements of the quinone radical anions in isopropanol and density functional theory (DFT) calculations in vacuo show that this increase in the hfcs is mostly intrinsic to the quinones due to the electron-withdrawing ability of the short chain and is not a result of differences in the binding to the protein. The DFT calculations suggest that the main reason for the increased methyl proton hfcs is delocalization of the singly occupied molecular orbital onto the side chain, which leads to an increase of the spin density on the neighboring carbon, which carries methyl group.

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