Structural response of Photosystem 2 to iron deficiency: Characterization of a new Photosystem 2-IdiA complex from the cyanobacterium Thermosynechococcus elongatus BP-1 |
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Authors: | Julia E.-M. Lax Egbert J. Boekema Klaus-Peter Michel |
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Affiliation: | a Plant Biochemistry, Faculty of Biology, Ruhr-University Bochum, 44780 Bochum, Germany b Department of Biophysical Chemistry, GBB, University of Groningen, 9747 AG Groningen, The Netherlands c Molecular Cell Physiology, Faculty of Biology, Bielefeld University, 33501 Bielefeld, Germany |
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Abstract: | Iron deficiency triggers various processes in cyanobacterial cells of which the synthesis of an additional antenna system (IsiA) around photosystem (PS) 1 is well documented [T.S. Bibby, J. Nield, J. Barber, Iron deficiency induces the formation of an antenna ring around trimeric photosystem I in cyanobacteria, Nature 412 (2001) 743-745, E.J. Boekema, A. Hifney, A.E. Yakushevska, M. Piotrowski, W. Keegstra, S. Berry, K.P. Michel, E.K. Pistorius, J. Kruip, A giant chlorophyll-protein complex induced by iron deficiency in cyanobacteria, Nature 412 (2001) 745-748]. Here we show that PS2 also undergoes prominent structural changes upon iron deficiency: Prerequisite is the isolation and purification of a PS2-IdiA complex which is exclusively synthesized under these conditions. Immunoblotting in combination with size exclusion chromatography shows that IdiA is only bound to dimeric PS2. Using single particle analysis of negatively stained specimens, IdiA can be localized in averaged electron micrographs on top of the CP43 subunit facing the cytoplasmic side in a model derived from the known 3D structure of PS2 [B. Loll, J. Kern, W. Saenger, A. Zouni, J. Biesiadka, Towards complete cofactor arrangement in the 3.0 Å resolution structure of photosystem II, Nature 438 (2005) 1040-4]. The presence of IdiA as integral part of PS2 is the first example of a new PS2 protein being expressed under stress conditions, which is missing in highly purified PS2 complexes isolated from iron-sufficient cells. |
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Keywords: | β-DM, dodecyl-β- smallcaps" >d-maltoside EM, Electron microscopy IEC, ion exchange chromatography HIC, hydrophobic interaction chromatography MALDI-ToF, Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry PAGE, Polyacrylamide gel electrophoresis PS, Photosystem SEC, size exclusion chromatography |
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