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Photosynthetic water oxidation: the function of two extrinsic proteins
Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The solar energy accumulated by photosynthesis over billions of years is the sole source of energy available on Earth. Photosystem II (PSII) uses the sunlight to split water, an energetically unfavorable reaction where electrons and protons are extracted from water and oxygen is released as a by-product. Understanding this process is crucial for the future development of clean, renewable and unlimited energy sources, which can use sunlight to split water and produce hydrogen and electricity. In order to do so we need to understand how this is solved in plants.

I have been focusing on the role of two lumenal proteins associated with the thylakoid membrane PsbO and Cah3, in the water oxidation process. Convincing evidences have been presented supporting the hypothesis that bicarbonate acts as a proton acceptor in the water splitting process in PSII and the lumenal carbonic anhydrase, Cah3, supplies bicarbonate required for this function. The PsbO protein, an important constituent of the water-oxidizing complex, however, its function is still unknown. The PsbO protein undergoes a pH dependent conformational change that in turn influences its capacity to bind calcium and manganese, forming a catalytic Mn4Ca cluster in PSII. We propose that light-induced structural dynamics of the PsbO is of functional relevance for the regulation of proton release and for forming a proton sensing - proton transporting pathway. The cluster of conserved glutamic and aspartic acid residues in the PsbO protein acts as buffering antennae providing efficient acceptors of protons derived from substrate water molecules. Both proteins, Cah3 and PsbO have a conserved S-S bridge, required for proper folding and activity; therefore they are potential targets for red-ox regulation in lumen.

Abstract [sv]

Solenergi som omvandlats av fotosyntesen under miljarder av år är basen för nästan all energi på jorden. Fotosystem 2 använder solljuset till att oxidera vatten, ur energisynpunkt en ofördelaktig process, där elektroner och protoner extraheras från vattenmolekyler vilket ger upphov till syrgas som biprodukt. Förståelsen av denna process är viktig för att vi i framtiden skall kunna utveckla rena och förnyelsebara energislag i obegrensad mängd. Genom att efterlikna fotosyntesprocessen skulle vi i framtiden kunna utvecka artificiella system som använder solljuset till att sönderdela vatten för att producera vätgas eller elektrisitet. För att kunna göra det så måste vi kunna förstå hur dessa processer fungerar i växterna.

Min forskning har fokuserat på att förstå funktionen hos två av de proteiner, PsbO och Cah3, som deltar i sönderdelningen av vatten. Jag har visat, för första gången, att ett lumen karboanhydras, Cah3, deltar i regleringen av den process där vatten spjälkas. Jag postulerar att Cah3 underlättar bort transporten av protoner från det vattenoxiderande komplexet genom att generera bikarbonat lokalt, som kan fungera som proton transportör. PsbO proteinet genomgår en pH beroende konformationsförändring vilket påverkar dess kapacitet and binda calcium och mangan som i sin tur formar ett katalytiskt Mn4Ca center i fotosystem 2. Jag föreslår att en ljusberoende strukturförändring av Psbo är av funktionell betydelse för regleringen av protonfrigörandet och formar ett proton-avkännande och proton-transporterande system. Ett kluster av konserverande glutamat- och aspartat-aminosyror i PsbO proteinet fungerar som ett buffrande nätverk för protoner som frigörs vid oxidering av vatten. Båda dessa proteiner innerhåller S-S bryggor ock kan därför vara red-ox reglerade i lumen.

Place, publisher, year, edition, pages
Umeå: Fysiologisk botanik , 2007. , 50 p.
Keyword [en]
photosystem II, Psb0, Cah3, water oxidation
National Category
Botany
Identifiers
URN: urn:nbn:se:umu:diva-1476ISBN: 978-91-7264-481-6 (print)OAI: oai:DiVA.org:umu-1476DiVA: diva2:141185
Public defence
2008-01-18, KB3A9, KBC, Umeå University, Umeå, 10:00
Opponent
Supervisors
Available from: 2008-01-07 Created: 2008-01-07 Last updated: 2011-04-01Bibliographically approved
List of papers
1. A photosystem II-associated carbonic anhydrase regulates the efficiency of photosynthetic oxygen evolution
Open this publication in new window or tab >>A photosystem II-associated carbonic anhydrase regulates the efficiency of photosynthetic oxygen evolution
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2002 (English)In: The EMBO Journal, ISSN 0261-4189, Vol. 21, no 8, 1930–1938- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2865 (URN)
Available from: 2008-01-07 Created: 2008-01-07 Last updated: 2015-04-29Bibliographically approved
2. The PSII-associated Cah3 in Chlamydomonas enhances the O2 evolution rate by proton removal
Open this publication in new window or tab >>The PSII-associated Cah3 in Chlamydomonas enhances the O2 evolution rate by proton removal
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In: The EMBO journal, ISSN 0261-4189Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:umu:diva-2866 (URN)
Available from: 2008-01-07 Created: 2008-01-07Bibliographically approved
3. cluster of carboxylic groups in PsbO protein is involved in proton transfer from the water oxidizing complex of Photosystem II
Open this publication in new window or tab >>cluster of carboxylic groups in PsbO protein is involved in proton transfer from the water oxidizing complex of Photosystem II
2007 In: Biochimica et biophysica acta. Bioenergetics, ISSN 0005-2728, Vol. 1767, no 6, 434-440 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2867 (URN)
Available from: 2008-01-07 Created: 2008-01-07Bibliographically approved
4. PsbO protein of photosystem II: overexpression in Escherichia coli and the importance of a single disulfide bond for the protein structure stability
Open this publication in new window or tab >>PsbO protein of photosystem II: overexpression in Escherichia coli and the importance of a single disulfide bond for the protein structure stability
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Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-2868 (URN)
Available from: 2008-01-07 Created: 2008-01-07 Last updated: 2010-01-13Bibliographically approved
5. Structural dynamics of the manganese-stabilizing protein-effect of pH, calcium, and manganese
Open this publication in new window or tab >>Structural dynamics of the manganese-stabilizing protein-effect of pH, calcium, and manganese
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2005 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 44, no 46, 15182-15192 p.Article in journal (Refereed) Published
Abstract [en]

The photosystem-II-associated 33-kDa extrinsic manganese-stabilizing protein is found in all oxygen-evolving organisms. In this paper, we show that this protein undergoes pH-induced conformational changes in the physiological pH range. At a neutral pH of 7.2, the hydrophobic amino acid residues that are most likely located inside the barrel are "closed" and the protein binds neither Mn2+ nor Ca2+ ions. When the protein is transferred to a solution with a slightly acidic pH of 5.7, hydrophobic amino acid residues become exposed to the surrounding medium, enabling them to bind the fluorescent probe 8,1-ANS. At this pH-induced open state, Mn2+ and Ca2+ bind to the manganese-stabilizing protein. The pH values used in this study, 7.2 and 5.7, are typical of the pH found in the thylakoid lumen in the dark and light, respectively. A model is presented in which the manganese-stabilizing protein undergoes a pH-dependent conformational change that in turn influences its capacity to bind calcium and manganese. In this model, the proton-dependent conformational changes of the tertiary structure of the manganese-stabilizing protein are of functional relevance for the regulation of substrate (water) delivery to and product (proton) release from the water-oxidizing complex by forming a proton-sensing proton-transport pathway.

Place, publisher, year, edition, pages
Easton: American Chemical Society, 2005
Keyword
Anilino Naphthalenesulfonates/chemistry, Calcium/*pharmacology, DNA; Circular, Darkness, Hydrogen-Ion Concentration, Light, Manganese/*pharmacology, Models; Chemical, Photosystem II Protein Complex/*chemistry/drug effects/radiation effects, Protein Conformation/*drug effects, Protein Folding, Spectrometry; Fluorescence
Identifiers
urn:nbn:se:umu:diva-12831 (URN)doi:10.1021/bi0512750 (DOI)16285721 (PubMedID)
Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2015-04-29Bibliographically approved
6. Subsequent events to GTP binding by the plant PsbO protein: Structural changes, GTP hydrolysis and dissociation from the photosystem II complex
Open this publication in new window or tab >>Subsequent events to GTP binding by the plant PsbO protein: Structural changes, GTP hydrolysis and dissociation from the photosystem II complex
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2007 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1767, no 6, 500-508 p.Article in journal (Refereed) Published
Abstract [en]

Besides an essential role in optimizing water oxidation in photosystem II (PSII), it has been reported that the spinach PsbO protein binds GTP [C. Spetea, T. Hundal, B. Lundin, M. Heddad, I. Adamska, B. Andersson, Proc. Natl. Acad. Sci. U.S.A. 101 (2004) 1409–1414]. Here we predict four GTP-binding domains in the structure of spinach PsbO, all localized in the β-barrel domain of the protein, as judged from comparison with the 3D-structure of the cyanobacterial counterpart. These domains are not conserved in the sequences of the cyanobacterial or green algae PsbO proteins.MgGTP induces specific changes in the structure of the PsbO protein in solution, as detected by circular dichroism and intrinsic fluorescence spectroscopy. Spinach PsbO has a low intrinsic GTPase activity, which is enhanced fifteen-fold when the protein is associated with the PSII complex in its dimeric form. GTP stimulates the dissociation of PsbO from PSII under light conditions known to also release Mn2+ and Ca2+ ions from the oxygen-evolving complex and to induce degradation of the PSII reaction centre D1 protein. We propose the occurrence in higher plants of a PsbO-mediated GTPase activity associated with PSII, which has consequences for the function of the oxygen-evolving complex and D1 protein turnover.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2007
Keyword
Photosystem II, PsbO protein, GTPase, Oxygen-evolving complex, D1 protein
Identifiers
urn:nbn:se:umu:diva-2870 (URN)10.1016/j.bbabio.2006.10.009 (DOI)17223069 (PubMedID)
Available from: 2008-01-07 Created: 2008-01-07 Last updated: 2015-04-29Bibliographically approved
7. Comparative studies on the properties of the extrinsic manganese-stabilizing protein from higher plants and of a synthetic peptide of its C-terminus
Open this publication in new window or tab >>Comparative studies on the properties of the extrinsic manganese-stabilizing protein from higher plants and of a synthetic peptide of its C-terminus
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2003 (English)In: Biochimica et biophysica acta. Bioenergetics, ISSN 0005-2728, Vol. 1604, no 2, 95-104 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2871 (URN)
Available from: 2008-01-07 Created: 2008-01-07 Last updated: 2015-04-29Bibliographically approved

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