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Formation of tyrosine radicals in photosystem II under far-red illumination
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.ORCID iD: 0000-0002-6218-3039
2018 (English)In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 136, no 1, p. 93-106Article in journal (Refereed) Published
Abstract [en]

Photosystem II (PS II) contains two redox-active tyrosine residues on the donor side at symmetrical positions to the primary donor, P680. TyrZ, part of the water-oxidizing complex, is a preferential fast electron donor while TyrD is a slow auxiliary donor to P680 +. We used PS II membranes from spinach which were depleted of the water oxidation complex (Mn-depleted PS II) to study electron donation from both tyrosines by time-resolved EPR spectroscopy under visible and far-red continuous light and laser flash illumination. Our results show that under both illumination regimes, oxidation of TyrD occurs via equilibrium with TyrZ at pH 4.7 and 6.3. At pH 8.5 direct TyrD oxidation by P680 + occurs in the majority of the PS II centers. Under continuous far-red light illumination these reactions were less effective but still possible. Different photochemical steps were considered to explain the far-red light-induced electron donation from tyrosines and localization of the primary electron hole (P680 +) on the ChlD1 in Mn-depleted PS II after the far-red light-induced charge separation at room temperature is suggested.

Place, publisher, year, edition, pages
2018. Vol. 136, no 1, p. 93-106
Keywords [en]
Photosystem II, Tyrosine Z and D, electron transfer
National Category
Biochemistry and Molecular Biology
Research subject
Chemistry with specialization in Biophysics
Identifiers
URN: urn:nbn:se:uu:diva-320914DOI: 10.1007/s11120-017-0442-3ISI: 000427394300007PubMedID: 28924898OAI: oai:DiVA.org:uu-320914DiVA, id: diva2:1091552
Funder
Swedish Research CouncilAvailable from: 2017-04-27 Created: 2017-04-27 Last updated: 2018-05-16Bibliographically approved
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. p. 72
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1527
Keywords
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)
Opponent
Supervisors
Available from: 2017-06-01 Created: 2017-04-27 Last updated: 2017-06-08

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