title: Two Different Structures of the Oxygen-Evolving Complex in the Same Polypeptide Frameworks of Photosystem II.
abstract: The oxygen-evolving complex (OEC) forms the heart of photosystem II (PSII) in photosynthesis. The crystal structure of PSII from Thermosynechococcus vulcanus has been reported at a resolution of 1.9 Å and at an averaged X-ray dose of 0.43 MGy. The OEC structure is suggested to be partially reduced to Mn(II) by EXAFS and DFT computational studies. Recently, the "radiation-damage-free" structures have been published at 1.95 Å resolution using XFEL, but reports continued to appear that the OEC is reduced to the S0-state of the Kok cycle. To elucidate much more precise structure of the OEC, in this study two structures were determined at extremely low X-ray doses of 0.03 and 0.12 MGy using conventional synchrotron radiation source. The results indicated that the X-ray reduction effects on the OEC were very small in the low dose region below 0.12 MGy, that is, a threshold existed for the OEC structural changes caused by X-ray exposure. The OEC structures of the two identical monomers in the crystal were clearly different under the threshold of the radiation dose, although the surrounding polypeptide frameworks of PSII were the same. The assumption that the OECs in the crystal were in the dark-stable S1-state of the Kok cycle should be re-evaluated.
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka City University , 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Tanaka
authors.affiliation: The OCU Advanced Research Institute for Natural Science and Technology (OCARINA), Osaka City University , 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Fukushima
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka City University , 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.|The OCU Advanced Research Institute for Natural Science and Technology (OCARINA), Osaka City University , 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585, Japan.
authors.forename: Nobuo
authors.identifier: 0000-0002-9056-7558
authors.initials: N
authors.lastname: Kamiya