Electron transfer in cyanobacterial photosystem I. I. Physiological and spectroscopic characterization of site-directed mutants in a putative electron transfer pathway from A0 through A1 to Fx

Wu Xu, Parag Chitnis, Alfia Valieva, Art Van der Est, Yulia N. Pushkar, Maciej Krzystyniak, Christian Teutloff, Stephan G. Zech, Robert Bittl, Dietmar Stehlik, Boris Zybailov, Gaozhong Shen, John H. Golbeck

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Abstract

The Photosystem I (PSI) reaction center contains two branches of nearly symmetric cofactors bound to the PsaA and PsaB heterodimer. From the x-ray crystal structure it is known that Trp697PsaA and Trp677PsaB are π-stacked with the head group of the phylloquinones and are H-bonded to Ser692PsaA and Ser672PsaB, whereas Arg694PsaA and Arg674PsaB are involved in a H-bonded network of side groups that connects the binding environments of the phylloquinones and Fx. The mutants W697FPsaA, W677FPsaB, S692CPsaA, S672CPsaB, R694APsaA, and R674APsaB were constructed and characterized. All mutants grew photoautotrophically, yet all showed diminished growth rates compared with the wild-type, especially at higher light intensities. EPR and electron nuclear double resonance (ENDOR) studies at both room temperature and in frozen solution showed that the PsaB mutants were virtually identical to the wild-type, whereas significant effects were observed in the PsaA mutants. Spin polarized transient EPR spectra of the P700+A1- radical pair show that none of the mutations causes a significant change in the orientation of the measured phylloquinone. Pulsed ENDOR spectra reveal that the W697FPsaA mutation leads to about a 5% increase in the hyperfine coupling of the methyl group on the phylloquinone ring, whereas the S692CPsaA mutation causes a similar decrease in this coupling. The changes in the methyl hyperfine coupling are also reflected in the transient EPR spectra of P700+A1- and the CW EPR spectra of photoaccumulated A1-. We conclude that: (i) the transient EPR spectra at room temperature are predominantly from radical pairs in the PsaA branch of cofactors; (ii) at low temperature the electron cycle involving P700 and A1 similarly occurs along the PsaA branch of cofactors; and (iii) mutation of amino acids in close contact with the PsaA side quinone leads to changes in the spin density distribution of the reduced quinone observed by EPR.

Original languageEnglish (US)
Pages (from-to)27864-27875
Number of pages12
JournalJournal of Biological Chemistry
Volume278
Issue number30
DOIs
StatePublished - Jul 25 2003

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Vitamin K 1
Photosystem I Protein Complex
Paramagnetic resonance
Electrons
Mutation
Electron Spin Resonance Spectroscopy
Temperature
High intensity light
X-Rays
Light
Amino Acids
Growth
Crystal structure
X rays
benzoquinone

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this

Xu, Wu ; Chitnis, Parag ; Valieva, Alfia ; Van der Est, Art ; Pushkar, Yulia N. ; Krzystyniak, Maciej ; Teutloff, Christian ; Zech, Stephan G. ; Bittl, Robert ; Stehlik, Dietmar ; Zybailov, Boris ; Shen, Gaozhong ; Golbeck, John H. / Electron transfer in cyanobacterial photosystem I. I. Physiological and spectroscopic characterization of site-directed mutants in a putative electron transfer pathway from A0 through A1 to Fx. In: Journal of Biological Chemistry. 2003 ; Vol. 278, No. 30. pp. 27864-27875.
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title = "Electron transfer in cyanobacterial photosystem I. I. Physiological and spectroscopic characterization of site-directed mutants in a putative electron transfer pathway from A0 through A1 to Fx",
abstract = "The Photosystem I (PSI) reaction center contains two branches of nearly symmetric cofactors bound to the PsaA and PsaB heterodimer. From the x-ray crystal structure it is known that Trp697PsaA and Trp677PsaB are π-stacked with the head group of the phylloquinones and are H-bonded to Ser692PsaA and Ser672PsaB, whereas Arg694PsaA and Arg674PsaB are involved in a H-bonded network of side groups that connects the binding environments of the phylloquinones and Fx. The mutants W697FPsaA, W677FPsaB, S692CPsaA, S672CPsaB, R694APsaA, and R674APsaB were constructed and characterized. All mutants grew photoautotrophically, yet all showed diminished growth rates compared with the wild-type, especially at higher light intensities. EPR and electron nuclear double resonance (ENDOR) studies at both room temperature and in frozen solution showed that the PsaB mutants were virtually identical to the wild-type, whereas significant effects were observed in the PsaA mutants. Spin polarized transient EPR spectra of the P700+A1- radical pair show that none of the mutations causes a significant change in the orientation of the measured phylloquinone. Pulsed ENDOR spectra reveal that the W697FPsaA mutation leads to about a 5{\%} increase in the hyperfine coupling of the methyl group on the phylloquinone ring, whereas the S692CPsaA mutation causes a similar decrease in this coupling. The changes in the methyl hyperfine coupling are also reflected in the transient EPR spectra of P700+A1- and the CW EPR spectra of photoaccumulated A1-. We conclude that: (i) the transient EPR spectra at room temperature are predominantly from radical pairs in the PsaA branch of cofactors; (ii) at low temperature the electron cycle involving P700 and A1 similarly occurs along the PsaA branch of cofactors; and (iii) mutation of amino acids in close contact with the PsaA side quinone leads to changes in the spin density distribution of the reduced quinone observed by EPR.",
author = "Wu Xu and Parag Chitnis and Alfia Valieva and {Van der Est}, Art and Pushkar, {Yulia N.} and Maciej Krzystyniak and Christian Teutloff and Zech, {Stephan G.} and Robert Bittl and Dietmar Stehlik and Boris Zybailov and Gaozhong Shen and Golbeck, {John H.}",
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Electron transfer in cyanobacterial photosystem I. I. Physiological and spectroscopic characterization of site-directed mutants in a putative electron transfer pathway from A0 through A1 to Fx. / Xu, Wu; Chitnis, Parag; Valieva, Alfia; Van der Est, Art; Pushkar, Yulia N.; Krzystyniak, Maciej; Teutloff, Christian; Zech, Stephan G.; Bittl, Robert; Stehlik, Dietmar; Zybailov, Boris; Shen, Gaozhong; Golbeck, John H.

In: Journal of Biological Chemistry, Vol. 278, No. 30, 25.07.2003, p. 27864-27875.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Electron transfer in cyanobacterial photosystem I. I. Physiological and spectroscopic characterization of site-directed mutants in a putative electron transfer pathway from A0 through A1 to Fx

AU - Xu, Wu

AU - Chitnis, Parag

AU - Valieva, Alfia

AU - Van der Est, Art

AU - Pushkar, Yulia N.

AU - Krzystyniak, Maciej

AU - Teutloff, Christian

AU - Zech, Stephan G.

AU - Bittl, Robert

AU - Stehlik, Dietmar

AU - Zybailov, Boris

AU - Shen, Gaozhong

AU - Golbeck, John H.

PY - 2003/7/25

Y1 - 2003/7/25

N2 - The Photosystem I (PSI) reaction center contains two branches of nearly symmetric cofactors bound to the PsaA and PsaB heterodimer. From the x-ray crystal structure it is known that Trp697PsaA and Trp677PsaB are π-stacked with the head group of the phylloquinones and are H-bonded to Ser692PsaA and Ser672PsaB, whereas Arg694PsaA and Arg674PsaB are involved in a H-bonded network of side groups that connects the binding environments of the phylloquinones and Fx. The mutants W697FPsaA, W677FPsaB, S692CPsaA, S672CPsaB, R694APsaA, and R674APsaB were constructed and characterized. All mutants grew photoautotrophically, yet all showed diminished growth rates compared with the wild-type, especially at higher light intensities. EPR and electron nuclear double resonance (ENDOR) studies at both room temperature and in frozen solution showed that the PsaB mutants were virtually identical to the wild-type, whereas significant effects were observed in the PsaA mutants. Spin polarized transient EPR spectra of the P700+A1- radical pair show that none of the mutations causes a significant change in the orientation of the measured phylloquinone. Pulsed ENDOR spectra reveal that the W697FPsaA mutation leads to about a 5% increase in the hyperfine coupling of the methyl group on the phylloquinone ring, whereas the S692CPsaA mutation causes a similar decrease in this coupling. The changes in the methyl hyperfine coupling are also reflected in the transient EPR spectra of P700+A1- and the CW EPR spectra of photoaccumulated A1-. We conclude that: (i) the transient EPR spectra at room temperature are predominantly from radical pairs in the PsaA branch of cofactors; (ii) at low temperature the electron cycle involving P700 and A1 similarly occurs along the PsaA branch of cofactors; and (iii) mutation of amino acids in close contact with the PsaA side quinone leads to changes in the spin density distribution of the reduced quinone observed by EPR.

AB - The Photosystem I (PSI) reaction center contains two branches of nearly symmetric cofactors bound to the PsaA and PsaB heterodimer. From the x-ray crystal structure it is known that Trp697PsaA and Trp677PsaB are π-stacked with the head group of the phylloquinones and are H-bonded to Ser692PsaA and Ser672PsaB, whereas Arg694PsaA and Arg674PsaB are involved in a H-bonded network of side groups that connects the binding environments of the phylloquinones and Fx. The mutants W697FPsaA, W677FPsaB, S692CPsaA, S672CPsaB, R694APsaA, and R674APsaB were constructed and characterized. All mutants grew photoautotrophically, yet all showed diminished growth rates compared with the wild-type, especially at higher light intensities. EPR and electron nuclear double resonance (ENDOR) studies at both room temperature and in frozen solution showed that the PsaB mutants were virtually identical to the wild-type, whereas significant effects were observed in the PsaA mutants. Spin polarized transient EPR spectra of the P700+A1- radical pair show that none of the mutations causes a significant change in the orientation of the measured phylloquinone. Pulsed ENDOR spectra reveal that the W697FPsaA mutation leads to about a 5% increase in the hyperfine coupling of the methyl group on the phylloquinone ring, whereas the S692CPsaA mutation causes a similar decrease in this coupling. The changes in the methyl hyperfine coupling are also reflected in the transient EPR spectra of P700+A1- and the CW EPR spectra of photoaccumulated A1-. We conclude that: (i) the transient EPR spectra at room temperature are predominantly from radical pairs in the PsaA branch of cofactors; (ii) at low temperature the electron cycle involving P700 and A1 similarly occurs along the PsaA branch of cofactors; and (iii) mutation of amino acids in close contact with the PsaA side quinone leads to changes in the spin density distribution of the reduced quinone observed by EPR.

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