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The protonation state around Tyr(D)/Tyr((D)) over dot in photosystem II is reflected in its biphasic oxidation kinetics
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Stockholm Univ, Dept Biochem & Biophys, Arrhenius Labs Nat Sci, SE-10691 Stockholm, Sweden..
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics. Imperial Coll London, Dept Life Sci, Sir Ernst Chain Bldg, London SW7 2AZ, England..
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2017 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1858, no 2, 147-155 p.Article in journal (Refereed) Published
Abstract [en]

The tyrosine residue D2-Tyr160 (Tyr(D)) in photosystem II (PSII) can be oxidized through charge equilibrium with the oxygen evolving complex in PSII. The kinetics of the electron transfer from Tyr(D) has been followed using time resolved EPR spectroscopy after triggering the oxidation of pre-reduced Tyr(D) by a short laser flash. After its oxidation Tyro is observed as a neutral radical (Tyr((D)) over dot) indicating that the oxidation is coupled to a deprotonation event. The redox state of Tyro 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 Tyr(D) the oxidation kinetics has been followed in the presence of deuterated buffers, thereby resolving the kinetic isotope effect (KIE) of Tyro oxidation at different H/D concentrations. Two kinetic phases of Tyro 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 (similar to 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 Tyro.

Place, publisher, year, edition, pages
2017. Vol. 1858, no 2, 147-155 p.
Keyword [en]
Photosystem II, Tyrosine D, Electron transfer, Proton transfer, Deuterium isotope effect
National Category
Biochemistry and Molecular Biology Biophysics
Identifiers
URN: urn:nbn:se:uu:diva-316938DOI: 10.1016/j.bbabio.2016.11.002ISI: 000392776400007PubMedID: 27823941OAI: oai:DiVA.org:uu-316938DiVA: diva2:1079647
Funder
Swedish Research Council, 621-2013-5937Swedish Energy Agency, 11674-5Knut and Alice Wallenberg Foundation, KAW 2011.0067
Available from: 2017-03-09 Created: 2017-03-09 Last updated: 2017-04-30
In thesis
1. Studies of the two redox active tyrosines in Photosystem II
Open this publication in new window or tab >>Studies of the two redox active tyrosines in Photosystem II
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Photosystem II is a unique enzyme which catalyzes light induced water oxidation. This process is driven by highly oxidizing ensemble of four Chl molecules, PD1, PD2, ChlD1 and ChlD2 called, P680. Excitation of one of the Chls in P680 leads to the primary charge separation, P680+Pheo-. Pheo- transfers electrons sequentially to the primary quinone acceptor QA and the secondary quinone acceptor QB. P680+ in turn extracts electrons from Mn4CaO5 cluster, a site for the water oxidation. There are two redox active tyrosines, TyrZ and TyrD, found in PSII. They are symmetrically located on the D1 and D2 central proteins. Only TyrZ acts as intermediate electron carrier between P680 and Mn4CaO5 cluster, while TyrD does not participate in the linear electron flow and stays oxidized under light conditions. Both tyrosines are involved in PCET.

The reduced TyrD undergoes biphasic oxidation with the fast (msec-sec time range) and the slow (tens of seconds time range) kinetic phases. We assign these phases to two populations of PSII centers with proximal or distal water positions. We also suggest that the TyrD oxidation and stability is regulated by the new small lumenal protein subunit, PsbTn. The possible involvement of PsbTn protein in the proton translocation mechanism from TyrD is suggested.

To assess the possible localization of primary cation in P680 the formation of the triplet state of P680 and the oxidation of TyrZ and TyrD were followed under visible and far-red light. We proposed that far-red light induces the cation formation on ChlD1.

Transmembrane interaction between QB and TyrZ has been studied. The different oxidation yield of TyrZ, measured as a S1 split EPR signal was correlated to the conformational change of protein induced by the QB presence at the QB-site. The change is transferred via H-bonds to the corresponding His-residues via helix D of the D1 protein.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 72 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1527
Keyword
Photosystem II, Tyrosine Z and D, proton-coupled electron transfer
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-320916 (URN)978-91-554-9933-4 (ISBN)
Public defence
2017-06-14, Room 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
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Available from: 2017-06-01 Created: 2017-04-27 Last updated: 2017-06-08

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