The protonation state around TyrD/TyrD in photosystem II is reflected in its biphasic oxidation kinetics

Johannes Sjöholm, Felix Ho, Nigar Ahmadova, Katharina Brinkert, Leif Hammarström, Fikret Mamedov, Stenbjörn Styring

Research output: Contribution to journalArticle

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Abstract

The tyrosine residue D2-Tyr160 (TyrD) in photosystem II (PSII) can be oxidized through charge equilibrium with the oxygen evolving complex in PSII. The kinetics of the electron transfer from TyrD has been followed using time-resolved EPR spectroscopy after triggering the oxidation of pre-reduced TyrD by a short laser flash. After its oxidation TyrD is observed as a neutral radical (TyrD ) indicating that the oxidation is coupled to a deprotonation event. The redox state of TyrD was reported to be determined by the two water positions identified in the crystal structure of PSII [Saito et al. (2013) Proc. Natl. Acad. Sci. USA 110, 7690]. To assess the mechanism of the proton coupled electron transfer of TyrD the oxidation kinetics has been followed in the presence of deuterated buffers, thereby resolving the kinetic isotope effect (KIE) of TyrD oxidation at different H/D concentrations. Two kinetic phases of TyrD oxidation – the fast phase (msec-sec time range) and the slow phase (tens of seconds time range) were resolved as was previously reported [Vass and Styring (1991) Biochemistry 30, 830]. In the presence of deuterated buffers the kinetics was significantly slower compared to normal buffers. Furthermore, although the kinetics were faster at both high pH and pD values the observed KIE was found to be similar (~ 2.4) over the whole pL range investigated. We assign the fast and slow oxidation phases to two populations of PSII centers with different water positions, proximal and distal respectively, and discuss possible deprotonation events in the vicinity of TyrD.

Original languageEnglish
Pages (from-to)147-155
Number of pages9
JournalBiochimica et Biophysica Acta - Bioenergetics
Volume1858
Issue number2
DOIs
Publication statusPublished - Feb 1 2017

Fingerprint

Photosystem II Protein Complex
Protonation
Tyrosine
Oxidation
Kinetics
Buffers
Deprotonation
Isotopes
Electrons
Biochemistry
Water
Oxidation-Reduction
Paramagnetic resonance
Protons
Spectrum Analysis
Lasers
Crystal structure
Spectroscopy
Oxygen

Keywords

  • Deuterium isotope effect
  • Electron transfer
  • Photosystem II
  • Proton transfer
  • Tyrosine D

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

Cite this

The protonation state around TyrD/TyrD in photosystem II is reflected in its biphasic oxidation kinetics. / Sjöholm, Johannes; Ho, Felix; Ahmadova, Nigar; Brinkert, Katharina; Hammarström, Leif; Mamedov, Fikret; Styring, Stenbjörn.

In: Biochimica et Biophysica Acta - Bioenergetics, Vol. 1858, No. 2, 01.02.2017, p. 147-155.

Research output: Contribution to journalArticle

Sjöholm, Johannes ; Ho, Felix ; Ahmadova, Nigar ; Brinkert, Katharina ; Hammarström, Leif ; Mamedov, Fikret ; Styring, Stenbjörn. / The protonation state around TyrD/TyrD in photosystem II is reflected in its biphasic oxidation kinetics. In: Biochimica et Biophysica Acta - Bioenergetics. 2017 ; Vol. 1858, No. 2. pp. 147-155.
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AU - Sjöholm, Johannes

AU - Ho, Felix

AU - Ahmadova, Nigar

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AU - Mamedov, Fikret

AU - Styring, Stenbjörn

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N2 - The tyrosine residue D2-Tyr160 (TyrD) in photosystem II (PSII) can be oxidized through charge equilibrium with the oxygen evolving complex in PSII. The kinetics of the electron transfer from TyrD has been followed using time-resolved EPR spectroscopy after triggering the oxidation of pre-reduced TyrD by a short laser flash. After its oxidation TyrD is observed as a neutral radical (TyrD •) indicating that the oxidation is coupled to a deprotonation event. The redox state of TyrD was reported to be determined by the two water positions identified in the crystal structure of PSII [Saito et al. (2013) Proc. Natl. Acad. Sci. USA 110, 7690]. To assess the mechanism of the proton coupled electron transfer of TyrD the oxidation kinetics has been followed in the presence of deuterated buffers, thereby resolving the kinetic isotope effect (KIE) of TyrD oxidation at different H/D concentrations. Two kinetic phases of TyrD oxidation – the fast phase (msec-sec time range) and the slow phase (tens of seconds time range) were resolved as was previously reported [Vass and Styring (1991) Biochemistry 30, 830]. In the presence of deuterated buffers the kinetics was significantly slower compared to normal buffers. Furthermore, although the kinetics were faster at both high pH and pD values the observed KIE was found to be similar (~ 2.4) over the whole pL range investigated. We assign the fast and slow oxidation phases to two populations of PSII centers with different water positions, proximal and distal respectively, and discuss possible deprotonation events in the vicinity of TyrD.

AB - The tyrosine residue D2-Tyr160 (TyrD) in photosystem II (PSII) can be oxidized through charge equilibrium with the oxygen evolving complex in PSII. The kinetics of the electron transfer from TyrD has been followed using time-resolved EPR spectroscopy after triggering the oxidation of pre-reduced TyrD by a short laser flash. After its oxidation TyrD is observed as a neutral radical (TyrD •) indicating that the oxidation is coupled to a deprotonation event. The redox state of TyrD was reported to be determined by the two water positions identified in the crystal structure of PSII [Saito et al. (2013) Proc. Natl. Acad. Sci. USA 110, 7690]. To assess the mechanism of the proton coupled electron transfer of TyrD the oxidation kinetics has been followed in the presence of deuterated buffers, thereby resolving the kinetic isotope effect (KIE) of TyrD oxidation at different H/D concentrations. Two kinetic phases of TyrD oxidation – the fast phase (msec-sec time range) and the slow phase (tens of seconds time range) were resolved as was previously reported [Vass and Styring (1991) Biochemistry 30, 830]. In the presence of deuterated buffers the kinetics was significantly slower compared to normal buffers. Furthermore, although the kinetics were faster at both high pH and pD values the observed KIE was found to be similar (~ 2.4) over the whole pL range investigated. We assign the fast and slow oxidation phases to two populations of PSII centers with different water positions, proximal and distal respectively, and discuss possible deprotonation events in the vicinity of TyrD.

KW - Deuterium isotope effect

KW - Electron transfer

KW - Photosystem II

KW - Proton transfer

KW - Tyrosine D

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