Yano Junko, Kern Jan, Yachandra Vittal K, Nilsson Håkan, Koroidov Sergey, Messinger Johannes
Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA,
Met Ions Life Sci. 2015;15:13-43. doi: 10.1007/978-3-319-12415-5_2.
Oxygen, that supports all aerobic life, is abundant in the atmosphere because of its constant regeneration by photosynthetic water oxidation, which is catalyzed by a Mn₄CaO₅ cluster in photosystem II (PS II), a multi subunit membrane protein complex. X-ray and other spectroscopy studies of the electronic and geometric structure of the Mn₄CaO₅ cluster as it advances through the intermediate states have been important for understanding the mechanism of water oxidation. The results and interpretations, especially from X-ray spectroscopy studies, regarding the geometric and electronic structure and the changes as the system proceeds through the catalytic cycle will be summarized in this review. This review will also include newer methodologies in time-resolved X-ray diffraction and spectroscopy that have become available since the commissioning of the X-ray free electron laser (XFEL) and are being applied to study the oxygen-evolving complex (OEC). The femtosecond X-ray pulses of the XFEL allows us to outrun X-ray damage at room temperature, and the time-evolution of the photo-induced reaction can be probed using a visible laser-pump followed by the X-ray-probe pulse. XFELs can be used to simultaneously determine the light-induced protein dynamics using crystallography and the local chemistry that occurs at the catalytic center using X-ray spectroscopy under functional conditions. Membrane inlet mass spectrometry has been important for providing direct information about the exchange of substrate water molecules, which has a direct bearing on the mechanism of water oxidation. Moreover, it has been indispensable for the time-resolved X-ray diffraction and spectroscopy studies and will be briefly reviewed in this chapter. Given the role of PS II in maintaining life in the biosphere and the future vision of a renewable energy economy, understanding the structure and mechanism of the photosynthetic water oxidation catalyst is an important goal for the future.
氧气支持所有需氧生命，由于其通过光合水氧化不断再生，所以在大气中含量丰富。光合水氧化由光系统II（PS II）中的Mn₄CaO₅簇催化，PS II是一种多亚基膜蛋白复合物。当Mn₄CaO₅簇通过中间状态时，对其电子和几何结构进行的X射线及其他光谱研究，对于理解水氧化机制很重要。本综述将总结关于几何和电子结构以及系统在催化循环过程中变化的结果和解释，特别是来自X射线光谱研究的结果。本综述还将包括时间分辨X射线衍射和光谱学中的新方法，这些方法自X射线自由电子激光（XFEL）投入使用以来已可用，并正被应用于研究析氧复合物（OEC）。XFEL的飞秒X射线脉冲使我们能够在室温下避免X射线损伤，并且可以使用可见激光泵浦随后的X射线探测脉冲来探测光诱导反应的时间演化。XFEL可用于在功能条件下，通过晶体学同时确定光诱导的蛋白质动力学，并通过X射线光谱学确定催化中心发生的局部化学过程。膜进样质谱对于提供有关底物水分子交换的直接信息很重要，这与水氧化机制直接相关。此外，它对于时间分辨X射线衍射和光谱学研究不可或缺，本章将对其进行简要综述。鉴于PS II在维持生物圈生命中的作用以及可再生能源经济的未来愿景，了解光合水氧化催化剂的结构和机制是未来的一个重要目标。
