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Visible light induction of an EPR split signal in photosystem II in the S2 state reveals the importance of charges in the oxygen evolving center during catalysis: a unifying model
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.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
2012 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 51, no 10, 2054-2064 p.Article in journal (Refereed) Published
Abstract [en]

Cryogenic illumination of Photosystem II (PSII) can lead to the trapping of the metastable radical Y-z(center dot), the radical form of the redox-active tyrosine residue D1-Tyr161 (known as Y-z). Magnetic interaction between this radical and the CaMn4 cluster of PSII gives rise to so-called split electron paramagnetic resonance (EPR) signals with characteristics that are dependent on the S state. We report here the observation and characterization of a split EPR signal that can be directly induced from PSII centers in the S-2 state through visible light illumination at 10 K. We further show that the induction of this split signal takes place via a Mn-centered mechanism, in the same way as when using near-infrared light illumination [Koulougliotis, D., et al. (2003) Biochemistry 42, 3045-3053]. On the basis of interpretations of these results, and in combination with literature data for other split signals induced under a variety of conditions (temperature and light quality), we propose a unified model for the mechanisms of split signal induction across the four S states (S-0, S-1, S-2, and S-3). At the heart of this model is the stability or instability of the Y-z(center dot)(D1-His190)(+) pair that would be formed during cryogenic oxidation of Y-Z. Furthermore, the model is closely related to the sequence of transfers of protons and electrons from the CaMn4, cluster during the S cycle and further demonstrates the utility of the split signals in probing the immediate environment of the oxygen-evolving center in PSII.

Place, publisher, year, edition, pages
2012. Vol. 51, no 10, 2054-2064 p.
National Category
Biophysics Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:uu:diva-173573DOI: 10.1021/bi2015794ISI: 000301398000004PubMedID: 22352968OAI: oai:DiVA.org:uu-173573DiVA: diva2:524084
Available from: 2012-04-27 Created: 2012-04-27 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Trapping Tyrosine Z: Exploring the Relay between Photochemistry and Water Oxidation in Photosystem II
Open this publication in new window or tab >>Trapping Tyrosine Z: Exploring the Relay between Photochemistry and Water Oxidation in Photosystem II
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Photosystem II is unique! It remains the only enzyme that can oxidize water using light as energy input. Water oxidation in photosystem II is catalyzed by the CaMn4 cluster. The electrons extracted from the CaMn4 cluster are transferred to P680+ via the tyrosine residue D1-Tyr161 (YZ). Favorable oxidation of YZ is coupled to a proton transfer along a hydrogen bond to the nearby D1-His190 residue, resulting in the neutral radical YZ. By illuminating photosystem II at cryogenic temperatures, YZ can be trapped in a stable state. Magnetic interaction between this radical and the CaMn4 cluster gives rise to a split electron paramagnetic resonance (EPR) signal with characteristics that depend on the oxidation state (S state) of the cluster.

The mechanism by which the split EPR signals are formed is different depending on the S state. In the S0 and S1 states, split signal induction proceeds via a P680+-centered mechanism, whereas in the S2 and S3 states, our results show that split induction stems from a Mn-centered mechanism. This S state-dependent pattern of split EPR signal induction can be correlated to the charge of the CaMn4 cluster in the S state in question and has prompted us to propose a general model for the induction mechanism across the different S states. At the heart of this model is the stability or otherwise of the YZ–(D1-His190)+ pair during cryogenic illumination. The model is closely related to the sequence of electron and proton transfers from the cluster during the S cycle.

Furthermore, the important hydrogen bond between YZ and D1-His190 has been investigated by following the split EPR signal formation in the different S states as a function of pH. All split EPR signals investigated decrease in intensity with a pKa of ~4-5. This pKa can be correlated to a titration event that disrupts the essential hydrogen bond, possibly by a direct protonation of D1-His190.  This has important consequences for the function of the CaMn4 cluster as this critical YZ–D1-His190 hydrogen bond steers a multitude of reactions at the cluster.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 943
Keyword
Photosystem II, Tyrosine Z, EPR, proton-coupled electron transfer, hydrogen bond, pH
National Category
Biochemistry and Molecular Biology Biophysics
Identifiers
urn:nbn:se:uu:diva-173575 (URN)978-91-554-8390-6 (ISBN)
Public defence
2012-06-15, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2012-05-25 Created: 2012-04-27 Last updated: 2012-08-01Bibliographically approved

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Styring, StenbjörnHo, Felix M.

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