Assessment of the manganese cluster's oxidation state via photoactivation of photosystem II microcrystals
Assessment of the manganese cluster's oxidation state via photoactivation of photosystem II microcrystals
复制标题
DOI：
10.1073/pnas.1915879117
复制
发表时间：
2020-01-07
影响因子：
11.1
通讯作者：
Messinger, Johannes
中科院分区：
文献类型：
--
作者：
Cheah, Mun Hon;Zhang, Miao;Messinger, Johannes
了解光系统 II (PSII) 中释氧 Mn4CaO5 簇的锰氧化态对于理解生物水氧化机制至关重要。关于这个话题存在长达 4 年的争论，历史上源于对多线电子顺磁共振 (EPR) 信号的观察，该信号在该簇的单氧化 S-2 态下有效总自旋为 S = 1/2。该信号意味着 S-2 态的总体氧化态为 Mn(III)(3)Mn(IV) 或 Mn(III)Mn(IV)(3)。这两个相互竞争的分配通常称为 Mn4CaO5 团簇的“低氧化 (LO)”和“高氧化 (HO)”模型。最近先进的 EPR 和 Mn K 边 X 射线光谱研究集中在 HO 模型上。然而，人们对这些任务提出了质疑，特别是通过计算从 Mn(II) 和 Mnfree PSII 开始组装活性 Mn4CaO5 簇所需的闪光驱动电子去除数量的研究，加剧了质疑。这个过程被称为光活化，似乎支持 LO 模型，因为据报道第一个氧气在 7 次闪光后就已经产生。在这项研究中，我们通过采用在完全去除锰后保留所有蛋白质亚基的 PSII 微晶体，并通过连接到膜入口质谱仪的定制薄层池进行氧检测，提高了光活化实验的量子产率和灵敏度。我们证明纳秒激光需要 9 次闪光才能产生第一个氧气，这证明 HO 模型提供了对 Mn4CaO5 团簇氧化态的正确描述。
Knowledge of the manganese oxidation states of the oxygenevolving Mn4CaO5 cluster in photosystem II (PSII) is crucial toward understanding the mechanism of biological water oxidation. There is a 4 decade long debate on this topic that historically originates from the observation of a multiline electron paramagnetic resonance (EPR) signal with effective total spin of S = 1/2 in the singly oxidized S-2 state of this cluster. This signal implies an overall oxidation state of either Mn(III)(3)Mn(IV) or Mn(III)Mn(IV)(3) for the S-2 state. These 2 competing assignments are commonly known as "low oxidation (LO)" and "high oxidation (HO)" models of the Mn4CaO5 cluster. Recent advanced EPR and Mn K-edge X-ray spectroscopy studies converge upon the HO model. However, doubts about these assignments have been voiced, fueled especially by studies counting the number of flash-driven electron removals required for the assembly of an active Mn4CaO5 cluster starting from Mn(II) and Mnfree PSII. This process, known as photoactivation, appeared to support the LO model since the first oxygen is reported to evolve already after 7 flashes. In this study, we improved the quantum yield and sensitivity of the photoactivation experiment by employing PSII microcrystals that retained all protein subunits after complete manganese removal and by oxygen detection via a custom built thin-layer cell connected to a membrane inlet mass spectrometer. We demonstrate that 9 flashes by a nanosecond laser are required for the production of the first oxygen, which proves that the HO model provides the correct description of the Mn4CaO5 cluster's oxidation states.