S1-state Mn4Ca complex of Photosystem II exists in equilibrium between the two most-stable isomeric substates: XRD and EXAFS evidence.
S1-state Mn4Ca complex of Photosystem II exists in equilibrium between the two most-stable isomeric substates: XRD and EXAFS evidence.
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Photosystem II 的 S1 态 Mn4Ca 复合物在两种最稳定的异构亚态之间处于平衡状态：XRD 和 EXAFS 证据。
DOI：
10.1016/j.jphotobiol.2011.03.002
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
M. Kusunoki
中科院分区：
文献类型：
--
作者：
M. Kusunoki
光系统II （PSII）中一个独特的Mn - 4ca簇催化的光合水氧化反应，在太阳的驱动下，发生在一个出氧复合体（OEC）中，循环五个系列氧化还原状态，称为“Kok 's S -states”（i= 0-4）。最近，利用1.9 Å-resolution XRD数据[55]分析了vulcanus热聚球菌（Thermosynechococcus vulcanus） PSII的原子晶体结构。有趣的是，它揭示了一个不寻常的氧桥接mn4 - CaO - 5簇在暗稳定的s1态，例如不寻常的mono-μ 2-oxo-mono-μ 4-oxo-mono-μ 2-carboxylato桥连接Mn a（末端）和Mn b（中心）离子，原子距离为2.9 Å。利用UDFT/B3LYP/lacvp∗∗几何优化方法和ε= 4介质中化学完全OEC的截断簇模型表明，由于质子迁移引起的准可逆结构变化，s1中的OEC必须在最稳定的异构体基态（“s1a和s1b”）之间处于热平衡状态。巧合的是，我们发现在s1a和s1b中Mn - 4ca簇中Mn - a - Mn - b的距离分别为R ab= 3.32 Å和2.77 Å，因此在同分异构体平衡中Mn - a和Mn - b离子之间的视距离为2.94 Å，与实验R ab ~ 2.9 Å一致。同时，粉末PSII[45]的第一个全k范围EXAFS光谱被用来提供s1态OEC在s1a和s1b异构体之间处于热平衡的第二个实验证据。这些oec -异构体由化学必需的11个氨基酸残基、6个辅因子离子和9个必需水合水分子组成，其化学离子状态在生理pH 7左右，因此合理地满足了4个Mn离子处于氧化态（Mn a III/Mn b IV/Mn c III/Mn d IV）的生化电荷中性，骨架结构为MT-5J型和t形DD-4J型。发现这些氢键水分子填充了连接可能的底物/产物通道的空腔，从而按照“当前底物”（W1/W2与Mn a III结合）、“下一底物”（W4/W7）和“下一后一底物”（W5/W6与ca2 +结合）的顺序排列成为催化Mn 4 Ca簇中不可或缺的一部分。结果表明，这些同分异构体中Mn - a - III离子的Jahn-Teller效应可以很好地解释时间分辨18 - o交换质谱在s1中观察到的极慢和极快交换过程。
Photosynthetic water oxidation reaction driven by Sun and catalyzed by a unique Mn 4 Ca cluster in Photosystem II (PSII) is known to take place in an oxygen evolving complex (OEC) that cycles five serial redox states, named “Kok’s S i-states”(i= 0–4). Recently, the atomic crystal structure of PSII from Thermosynechococcus vulcanus was resolved by 1.9 Å-resolution XRD data [55]. Interestingly, it revealed an unusual oxo-bridged Mn 4 CaO 5 cluster in the dark stable S 1-state, eg unusual mono-μ 2-oxo-mono-μ 4-oxo-mono-μ 2-carboxylato bridges connecting Mn a (terminal) and Mn b (central) ions with unusual atomic distance of 2.9 Å. Using the UDFT/B3LYP/lacvp∗∗ geometry optimization method and a truncated cluster model of the chemically-complete OEC put in ε= 4 dielectric medium, it is shown that the OEC in S 1 must be in thermal equilibrium between the most-stable isomeric substates (“S 1a and S 1b”) owing to the quasi-reversible structure change induced by proton migration. Coincidentally, it is found that the Mn a–Mn b distances in the Mn 4 Ca clusters in S 1a and S 1b are given by R ab= 3.32 Å and 2.77 Å, respectively, so that the apparent distance between Mn a and Mn b ions in isomeric equilibrium is given by 2.94 Å, in agreement with experimental R ab∼ 2.9 Å. Concomitantly, the first full-k-range EXAFS spectrum from powdered PSII [45] is used to provide the second experimental evidence for the S 1-state OEC being in thermal equilibrium between S 1a and S 1b-isomers. These OEC-isomers consist of all the chemically-essential 11 amino acid residues, six cofactor ions and nine essential hydrated water molecules in their chemical ionic states around physiological pH 7, thus reasonably satisfying the biochemical charge neutrality with four Mn ions staying at the oxidation states (Mn a III/Mn b IV/Mn c III/Mn d IV) with the skeleton structures of MT-5J type and T-shaped DD-4J type. These H-bonding water molecules are found to fill a cavity connecting possible substrate/products channels so as to be arranged as an indispensable part of the catalytic Mn 4 Ca cluster in the order of “current-substrates”(W1/W2 bound to Mn a III),“next-substrates”(W4/W7) and “next–after-next-substrates”(W5/W6 bound to Ca 2+). Results show that the Jahn–Teller effect due to Mn a III ion in these isomers can reasonably explain the very-slow-exchange and very-fast-exchange processes observed in S 1 by time-resolved 18 O-exchange mass spectroscopy.
影响因子：
15
作者：
Yano, J;Pushkar, Y;Yachandra, V
通讯作者：
Yachandra, V
DOI：
10.1073/pnas.0505207102
发表时间：
2005-08-23
影响因子：
11.1
作者：
Yano, J;Kern, J;Yachandra, VK
通讯作者：
Yachandra, VK