Yano Junko, Pushkar Yulia, Glatzel Pieter, Lewis Azul, Sauer Kenneth, Messinger Johannes, Bergmann Uwe, Yachandra Vittal
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J Am Chem Soc. 2005 Nov 2;127(43):14974-5. doi: 10.1021/ja054873a.
The biological generation of oxygen by the oxygen-evolving complex in photosystem II (PS II) is one of nature's most important reactions. The recent X-ray crystal structures, while limited by resolutions of 3.2-3.5 A, have located the electron density associated with the Mn4Ca cluster within the multiprotein PS II complex. Detailed structures critically depend on input from spectroscopic techniques, such as EXAFS and EPR/ENDOR, as the XRD resolution does not allow for accurate determination of the position of Mn/Ca or the bridging and terminal ligand atoms. The number and distances of Mn-Mn/Ca/ligand interactions determined from EXAFS provide important constraints for the structure of the Mn4Ca cluster. Here, we present data from a high-resolution EXAFS method using a novel multicrystal monochromator that show three short Mn-Mn distances between 2.7 and 2.8 A and, hence, the presence of three di-mu-oxo-bridged units in the Mn4Ca cluster. This result imposes clear limitations on the proposed structures based on spectroscopic and diffraction data and provides input for refining such structures.
光系统II（PS II）中光解水复合物产生氧气的生物过程是自然界最重要的反应之一。最近的X射线晶体结构虽受限于3.2 - 3.5埃的分辨率，但已在多蛋白PS II复合物中确定了与Mn4Ca簇相关的电子密度。由于X射线衍射（XRD）分辨率无法精确确定Mn/Ca的位置以及桥连和末端配体原子，详细结构严重依赖于诸如扩展X射线吸收精细结构（EXAFS）和电子顺磁共振/电子核双共振（EPR/ENDOR）等光谱技术的输入信息。由EXAFS确定的Mn - Mn/Ca/配体相互作用的数量和距离为Mn4Ca簇的结构提供了重要限制。在此，我们展示了使用新型多晶体单色仪的高分辨率EXAFS方法的数据，该数据显示在Mn4Ca簇中有三个2.7至2.8埃的短Mn - Mn距离，因此存在三个双μ - 氧桥连单元。这一结果对基于光谱和衍射数据提出的结构施加了明确限制，并为完善此类结构提供了信息。
