Differences in the Interactions between the Subunits of Photosystem II Dependent on D1 Protein Variants in the Thermophilic Cyanobacterium Thermosynechococcus elongatus |
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Authors: | Miwa Sugiura Eri Iwai Hidenori Hayashi Alain Boussac |
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Institution: | From the ‡Cell-Free Science and Technology Research Center and Venture Business Laboratory and ;the §Department of Chemistry, Ehime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan and ;¶iBiTec-S, CNRS URA 2096, CEA Saclay, 91191 Gif sur Yvette, France |
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Abstract: | The main cofactors involved in the oxygen evolution activity of Photosystem II (PSII) are located in two proteins, D1 (PsbA) and D2 (PsbD). In Thermosynechococcus elongatus, a thermophilic cyanobacterium, the D1 protein is encoded by either the psbA1 or the psbA3 gene, the expression of which is dependent on environmental conditions. It has been shown that the energetic properties of the PsbA1-PSII and those of the PsbA3-PSII differ significantly (Sugiura, M., Kato, Y., Takahashi, R., Suzuki, H., Watanabe, T., Noguchi, T., Rappaport, F., and Boussac, A. (2010) Biochim. Biophys. Acta 1797, 1491–1499). In this work the structural stability of PSII upon a PsbA1/PsbA3 exchange was investigated. Two deletion mutants lacking another PSII subunit, PsbJ, were constructed in strains expressing either PsbA1 or PsbA3. The PsbJ subunit is a 4-kDa transmembrane polypeptide that is surrounded by D1 (i.e. PsbA1), PsbK, and cytochrome b559 (Cyt b559) in existing three-dimensional models. It is shown that the structural properties of the PsbA3/ΔPsbJ-PSII are not significantly affected. The polypeptide contents, the Cyt b559 properties, and the proportion of PSII dimer were similar to those found for PsbA3-PSII. In contrast, in PsbA1/ΔPsbJ-PSII the stability of the dimer is greatly diminished, the EPR properties of the Cyt b559 likely indicates a decrease in its redox potential, and many other PSII subunits are lacking. These results shows that the 21-amino acid substitutions between PsbA1 and PsbA3, which appear to be mainly conservative, must include side chains that are involved in a network of interactions between PsbA and the other PSII subunits. |
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Keywords: | Electron Transfer Photosynthesis Protein Stability Protein Structure Site-directed Mutagenesis Photosystem II Thermosynechococcus elongatus Water Oxidation |
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