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Two Different Structures of the Oxygen-Evolving Complex in the Same Polypeptide Frameworks of Photosystem II
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2017-01-30 , DOI: 10.1021/jacs.6b09666
Ayako Tanaka 1 , Yoshimasa Fukushima 2 , Nobuo Kamiya 1, 2
Affiliation  

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.

中文翻译:

光系统 II 相同多肽框架中的两种不同结构的产氧复合物

析氧复合物 (OEC) 是光合作用中光系统 II (PSII) 的核心。据报道,来自 Thermosynechococcus vulcanus 的 PSII 的晶体结构的分辨率为 1.9 Å,平均 X 射线剂量为 0.43 MGy。通过 EXAFS 和 DFT 计算研究,建议 OEC 结构部分还原为 Mn(II)。最近,使用 XFEL 以 1.95 Å 分辨率发布了“无辐射损伤”结构,但仍有报道称 OEC 降低到 Kok 循环的 S0 状态。为了阐明 OEC 更精确的结构,在这项研究中,使用传统的同步辐射源在 0.03 和 0.12 MGy 的极低 X 射线剂量下确定了两种结构。结果表明,在0.12 MGy以下的低剂量区,X射线对OEC的降低作用很小,即X射线照射引起的OEC结构变化存在阈值。在辐射剂量阈值下,晶体中两种相同单体的 OEC 结构明显不同,尽管 PSII 的周围多肽框架相同。应该重新评估晶体中的 OEC 处于 Kok 循环的暗稳定 S1 状态的假设。
更新日期:2017-01-30
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