The structure and activation of substrate water molecules in Sr2+- substituted photosystem II
The structure and activation of substrate water molecules in Sr2+- substituted photosystem II
复制标题
Sr2取代光系统II中底物水分子的结构和活化
DOI：
10.1039/c4cp03082f
复制
发表时间：
2014
影响因子：
3.3
通讯作者：
Jian-Ren Shen and K.V. Lakshmi
中科院分区：
文献类型：
--
作者：
Ruchira Chatterjee;Sergey Milikisiyants;Christopher S. Coates;Faisal H.M. Koua;Jian-Ren Shen and K.V. Lakshmi
光系统 II (PSII) 的太阳水氧化机制具有重要意义，并且是过去和现在广泛研究的对象。 PSII 的太阳能水氧化反应发生在析氧络合物 (OEC) 中。 OEC 由四核锰钙-氧 (Mn4Ca-oxo) 簇组成，周围被氨基酸残基和无机辅助因子包围。 Ca2+ 离子在水氧化反应中的作用是尚未解答的最有趣的问题之一。在本研究中，我们通过用 Sr2+ 离子取代 OEC 中的 Ca2+ 离子，探讨了 Mn4Ca-oxo 簇中金属离子取代引起的结构和功能差异。我们应用二维 (2D) 超精细亚级相关 (HYSCORE) 光谱来检测 Sr2+ 取代的 PSII 的 OEC 的 S2 态中顺磁 Mn4Sr-oxo 团簇与周围质子之间的弱磁相互作用。我们确定了三组与 Mn4Sr-oxo 簇发生磁性相互作用的质子。使用最近报道的 S1 态 OEC 的 1.9 Å 分辨率 X 射线结构 [Umena 等人] 和含 Ca2+ PSII 的 OEC S2 态的高分辨率 2D HYSCORE 光谱研究 [Milikisyants 等人，Energy Environ. Sci., 2012, 5, 7747]，我们讨论了与 Mn4Sr-oxo 团簇磁耦合的三组质子的分配。由于超精细相互作用对顺磁中心的电子和几何结构中的小扰动高度敏感，因此通过比较 Sr2+ 取代的 PSII 和含 Ca2+ 的 PSII 的 2D HYSCORE 谱，我们可以得出关于 OEC 中底物水分子的结构以及 Ca2+ 离子在水氧化反应中的作用的重要结论。此外，我们首次根据顺磁团簇与 PSII 的 D1-His332 残基质子的超精细相互作用的分配，确定了 Mn4Ca-oxo 团簇的 Mn(III) 离子的自旋投影因子的实验值为 ρ1 = ±1.7。
The mechanism of solar water oxidation by photosystem II (PSII) is of fundamental interest and it is the object of extensive studies both in the past and present. The solar water oxidation reaction of PSII occurs in the oxygen-evolving complex (OEC). The OEC consists of a tetranuclear manganese calcium–oxo (Mn4Ca–oxo) cluster that is surrounded by amino acid residues and inorganic cofactors. The role of the Ca2+ ion in the water oxidation reaction is one of the most interesting questions that is yet to be answered. In this study, we probe the structural and functional differences induced by metal ion substitution in the Mn4Ca–oxo cluster by substituting the Ca2+ ion in the OEC by a Sr2+ ion. We apply two-dimensional (2D) hyperfine sublevel correlation (HYSCORE) spectroscopy to detect weak magnetic interactions between the paramagnetic Mn4Sr–oxo cluster and the surrounding protons in the S2 state of the OEC of Sr2+-substituted PSII. We identify three groups of protons that are magnetically interacting with the Mn4Sr–oxo cluster. Using the recently reported 1.9 Å resolution X-ray structure of the OEC in the S1 state [Umena et al.] and the high-resolution 2D HYSCORE spectroscopy studies of the S2 state of the OEC of Ca2+-containing PSII [Milikisiyants et al., Energy Environ. Sci., 2012, 5, 7747], we discuss the assignments of the three groups of protons that are magnetically coupled to the Mn4Sr–oxo cluster. Since hyperfine interactions are highly sensitive to small perturbations in the electronic and geometric structure of paramagnetic centers, a comparison of the 2D HYSCORE spectra of Sr2+-substituted and Ca2+-containing PSII allows us to draw important conclusions with respect to the structure of the substrate water molecules in the OEC and the role of the Ca2+ ion in the water oxidation reaction. In addition, for the first time, we determine the experimental value of the spin projection factor for the Mn(III) ion of the Mn4Ca–oxo cluster as ρ1 = ±1.7 from the assignment of the hyperfine interaction of the paramagnetic cluster with the protons of the D1-His332 residue of PSII.