Structural differences in the inner part of Photosystem II between higher plants and cyanobacteria |
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Authors: | Email author" target="_blank">Claudia?BüchelEmail author Werner?Kühlbrandt |
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Institution: | (1) Max Planck Institute of Biophysics, Marie Curie Strasse 13–15, 60439 Frankfurt, Germany |
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Abstract: | A detailed comparison of key components in the Photosystem II complexes of higher plants and cyanobacteria was carried out. While the two complexes are overall very similar, significant differences exist in the relative orientation of individual components relative to one another. We compared a three-dimensional map of the inner part of plant PS II at 8 Å resolution, and a 5.5 Å projection map of the same complex determined by electron crystallography, to the recent 3.5–3.8 Å X-ray structures of cyanobacterial complexes. The largest differences were found in the rotational alignment of the cyt b^559 subcomplex, and of the CP47 core antenna with respect to the D1/D2 reaction centre. Within the D1/D2 proteins, there are clear differences between plants and cyanobacteria at the stromal ends of membrane-spanning helices, even though these proteins are highly homologous. Notwithstanding these differences in the protein scaffold, the distances between the critical photosynthetic pigment cofactors seem to be precisely conserved. The different protein arrangements in the two complexes may reflect an adaptation to the two very different antenna systems, membrane-extrinsic phycobilisomes for cyanobacteria, and membrane-embedded chlorophyll a/b proteins in plants. |
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Keywords: | electron crystallography electron density map photosynthesis P680 X-ray crystallography |
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