The structure of the manganese complex of Photosystem II in its dark-stable S1-state-EXAFS results in relation to recent crystallographic data
The structure of the manganese complex of Photosystem II in its dark-stable S1-state-EXAFS results in relation to recent crystallographic data
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DOI：
10.1039/b408146c
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发表时间：
2004-01-01
影响因子：
3.3
通讯作者：
Haumann, M
中科院分区：
文献类型：
--
作者：
Dau, H;Liebisch, P;Haumann, M
光系统II（PSII）的Mn 4Ca复合物的核几何形状的测定可能有助于深入讨论光合水氧化的机制。通过EXAFS（扩展X射线吸收精细结构）光谱和蛋白质晶体学进行结构分析的第一步是确定Mn络合物的暗稳定S-1-态的结构。EXAFS光谱的归一化和模拟的方法进行了严格的评估，特别是相对于确定的配位数的准确性。结果表明，在Si态下，Mn-Mn相互作用的数目可能为2个，其长度约为2.7埃。通过EXAFS分析预测了2.7埃Mn-Mn矢量以及类似于3.3埃长度的Mn-Ca距离的存在和取向，并且似乎与可用的晶体学数据（Zouni，Witt，J.克恩，P. Fromme，N.克劳，W. Saenger和P. Orth，Nature，2001，409，Kamiya和Shen，Proc. Natl. Acad. Sci. USA，2003，100，98; Ferreira，Iverson，Maghlaoui，Barber和岩田，Science，2004，303，1831）。然而，在光的XAS结果辐射诱导的Mn 4Ca复合物的修改，我们得出结论，在晶体学数据收集的过程中的Mn 4Ca复合物可能会受到显着影响的X-射线光还原，使获得的电子密度图不代表完整的复合物在其S-1-状态。因此，结合EXAFS结果和晶体学数据进行任何详细的结构建模似乎都为时过早。Mn离子在配合物中的两种连接模式，即通过（mu（2）-O）（2）或（mu（2）-O，mu（3）-O）桥，可以解释Mn-Mn距离接近2.7埃。三个基本的可能性安排锰离子的Mn 4Ca配合物在其SI状态进行了讨论。
Determination of the nuclear geometry of the Mn4Ca complex of photosystem II (PSII) may facilitate an in-depth discussion of the mechanism of photosynthetic water oxidation. The first step of structural analysis by EXAFS (extended X-ray absorption fine-structure) spectroscopy and protein crystallography is the determination of the structure of the dark-stable S-1-state of the Mn complex. Approaches for normalization and simulation of EXAFS spectra are critically evaluated, in particular with respect to the accuracy of the determined coordination numbers. It is shown that the number of Mn-Mn interactions with about 2.7 Angstrom length is likely to be two in the SI-state. The presence and orientation of the 2.7 A Mn-Mn vectors as well as of the Mn-Ca distances of similar to3.3 Angstrom length is predicted by EXAFS analysis and seems to be compatible with the available crystallographic data (Zouni, Witt, J. Kern, P. Fromme, N. Krauu, W. Saenger and P. Orth, Nature, 2001, 409, Kamiya and Shen, Proc. Natl. Acad. Sci. USA, 2003, 100, 98; Ferreira, Iverson, Maghlaoui, Barber and Iwata, Science, 2004, 303, 1831). In the light of XAS results on radiation-induced modifications of the Mn4Ca complex, however, we conclude that in the course of the crystallographic data collection the Mn4Ca complex may be significantly affected by X-ray photoreduction so that the obtained electron density maps do not represent the intact complex in its S-1-state. Thus, any detailed structural modelling by combination of EXAFS results and crystallographic data seems to be premature. Two motifs for the connection of Mn ions in the complex, namely either by (mu(2)-O)(2) or (mu(2)-O, mu(3)-O) bridges, may account for Mn-Mn distances close to 2.7 Angstrom. Three basic possibilities to arrange the Mn ions of the Mn4Ca complex in its SI-state are discussed.