Role of a water network around the Mn4CaO5 cluster in photosynthetic water oxidation: A Fourier transform infrared spectroscopy and quantum mechanics/molecular mechanics calculation study
Role of a water network around the Mn4CaO5 cluster in photosynthetic water oxidation: A Fourier transform infrared spectroscopy and quantum mechanics/molecular mechanics calculation study
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Mn4CaO5团簇周围的水网络在光合水氧化中的作用：傅里叶变换红外光谱和量子力学/分子力学计算研究
DOI：
10.1021/acs.biochem.5b01120
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发表时间：
2016
期刊：
影响因子：
2.9
通讯作者：
T. Noguchi
中科院分区：
文献类型：
--
作者：
S. Nakamura;K. Ota;Y. Shibuya;T. Noguchi
光合水氧化发生在光系统 II 的 Mn4CaO5 簇中。在Mn4CaO5簇周围，由多个水分子形成氢键网络，其中包括四个水配体。为了阐明这种水网络在水氧化机制中的作用，我们通过傅里叶变换红外（FTIR）差分光谱和量子力学/分子力学（QM/MM）计算研究了Ca2+的去除和金属离子的取代对耦合到Mn4CaO5团簇的水分子振动的影响。使用QM/MM方法计算了在D1-D61和YZ之间形成网络的9个水分子的OH伸缩振动。在计算的简正模上，S2-S1FTIR 光谱中 3200–2500 cm–1 处的广泛正特征归因于水的强氢键 OH 键的振动，涉及水配体与 Mn 离子的振动以及连接到 YZ 的水网络的同相耦合振动，而 3700–3500 cm–1 区域中的谱带则归因于弱氢键的耦合振动水的OH键。所有水带在 Ca2+ 耗尽和 Ba2+ 取代时丢失，抑制了 S2→S3 转变，表明这些处理破坏了固体水网络。相比之下，Sr2+ 取代稍微改变了 3600 cm-1 附近的水带，反映了水相互作用的微小改变，与水氧化活性的保留和效率降低一致。这些结果表明，Mn4CaO5团簇周围的水网络在水氧化机制中起着至关重要的作用，特别是在S2→S3转变过程中质子转移和水插入的协调过程中。
Photosynthetic water oxidation takes place at the Mn4CaO5cluster in photosystem II. Around the Mn4CaO5cluster, a hydrogen bond network is formed by several water molecules, including four water ligands. To clarify the role of this water network in the mechanism of water oxidation, we investigated the effects of the removal of Ca2+and substitution with metal ions on the vibrations of water molecules coupled to the Mn4CaO5cluster by means of Fourier transform infrared (FTIR) difference spectroscopy and quantum mechanics/molecular mechanics (QM/MM) calculations. The OH stretching vibrations of nine water molecules forming a network between D1-D61 and YZwere calculated using the QM/MM method. On the the calculated normal modes, a broad positive feature at 3200–2500 cm–1in an S2-minus-S1FTIR spectrum was attributed to the vibrations of strongly hydrogen-bonded OH bonds of water involving the vibrations of water ligands to a Mn ion and the in-phase coupled vibration of a water network connected to YZ, while bands in the 3700–3500 cm–1region were assigned to the coupled vibrations of weakly hydrogen-bonded OH bonds of water. All the water bands were lost upon Ca2+depletion and Ba2+substitution, which inhibit the S2→ S3transition, indicating that a solid water network was broken by these treatments. By contrast, Sr2+substitution slightly altered the water bands around 3600 cm–1, reflecting minor modification in water interactions, consistent with the retention of water oxidation activity with a decreased efficiency. These results suggest that the water network around the Mn4CaO5cluster plays an essential role in the water oxidation mechanism particularly in a concerted process of proton transfer and water insertion during the S2→ S3transition.