Structure and Function of the Mn Oxygen-Evolving Complex

 描述(申请人提供)：含有氧化还原活性作用的锰的金属蛋白参与氧代谢的各种重要生理反应。其中包括将超氧阴离子自由基解毒为O2和过氧化氢的超氧化物歧化酶，将过氧化氢不成比例地分解为O2和H2O的过氧化氢酶，以及可能是最复杂和最重要的Mn4CaO5簇，它参与了光系统II(PS II)中水被氧化为二氧化氧的过程，PS II是一个~500 kDa的多亚单位膜蛋白复合体。PS II中的水氧化反应包括通过光诱导氧化以一种循序渐进的方式从两个水分子中移除四个电子，生成一个氧分子。PS II和Mn4CaO5团簇几乎产生了支持有氧生命的所有氧气，由于其通过水的氧化不断再生，因此在大气中含量丰富。光诱导水氧化成氧气是生物圈中发生的最重要的大规模化学过程之一。虽然PS II的结构和催化部位的化学已经被深入研究，但在原子尺度上理解从光吸收到水氧化的化学顺序需要一种新的方法，而不是传统的稳态X射线结晶学和低温X射线光谱学。在克服X射线对氧化还原活性中心的严重损伤的同时，跟踪PS II和Mn4CaO5团簇在常温下结构的动态变化，是推导这一机制的关键。LCLS(直线加速器相干光源)X射线自由电子激光器的高强度和超短飞秒X射线脉冲为克服目前在常规X射线源下收集生物样品的室温数据的局限性提供了机会。飞秒X射线脉冲使我们能够在样品被破坏之前获取信号，从而使这里提出的光诱导快照研究成为可能。我们的目标是用X射线衍射法研究PS II的蛋白质结构和动力学，以及用X射线光谱研究PS II光驱动过程中Mn4CaO5团簇的化学结构和动力学(电荷、自旋和共价性)。我们将把这些时间分辨的研究与利用先进的X射线吸收和发射光谱方法对稳态样品的研究结合起来。这些研究有可能提供PS II蛋白、辅助因子和Mn4CaO5簇之间前所未有的相关数据组合，提供几何结构和电子结构以及在催化循环中发生的变化，所有这些都是全面了解水氧化机制所必需的。

 DESCRIPTION (provided by applicant): Metalloproteins containing manganese in a redox-active role are involved in a variety of physiologically important reactions of dioxygen metabolism. These include, amongst others, a superoxide dismutase that detoxifies superoxide radicals to O2 and peroxide, a catalase that disproportionate peroxide to O2 and H2O, and perhaps the most complex and important, the Mn4CaO5 cluster that is involved in the oxidation of water to dioxygen in photosystem II (PS II), an ~500 kDa multi-subunit membrane protein complex. The water-oxidation reaction in PS II involves removal of four electrons, in a stepwise manner by light-induced oxidation, from two water molecules to produce a molecule of oxygen. PS II and the Mn4CaO5 cluster generate almost all of the dioxygen that supports aerobic life, and it is abundant in the atmosphere because of its constant regeneration by the oxidation of water. The light-induced oxidation of water to dioxygen is one of the most important chemical processes occurring on such a large scale in the biosphere. Although the structure of PS II and the chemistry at the catalytic site have been studied intensively, understanding the sequence in the chemistry at atomic-scale from light absorption to water-oxidation requires a new approach beyond the conventional steady state X-ray crystallography and X-ray spectroscopy at cryogenic temperatures. Following the dynamic changes in the structure of PS II and the Mn4CaO5 cluster at ambient conditions, while overcoming the severe X-ray damage to the redox active center, is key for deriving the mechanism. The intense and ultra-short femtosecond (fs) X-ray pulses of the LCLS (Linac Coherent Light Source) X-ray free electron laser provide an opportunity to overcome the current limitations of room temperature data collection for biological samples at regular X-ray sources. The fs X-ray pulses allow us to acquire the signal before the sample is destroyed, thus making the light-induced snap-shot study proposed here possible. The objective of this proposal is to study the protein structure and dynamics of PS II with X-ray diffraction, as well as the chemical structure and dynamics of the Mn4CaO5 cluster (charge, spin, and covalency) with X- ray spectroscopy during the light-driven process of PS II. We will combine these time-resolved studies with the study of samples in the steady state using advanced methods of X-ray absorption and emission spectroscopy. These studies have the potential to provide an unprecedented combination of correlated data between the PS II protein, the co-factors, and the Mn4CaO5 cluster, providing the geometric and electronic structure and the changes that occur during the catalytic cycle, all of which are necessary for a complete understanding of the mechanism of water oxidation.