Biophysical and Bioinorganic Studies of Oxygen Evolution

描述（由申请人提供）：光系统II（PSII）是一种膜蛋白复合物，利用光催化水氧化和醌还原。PSII的放氧复合物（OEC）是我们呼吸的大气氧气的来源。由于大气中的氧气是维持地球上所有有氧生命所必需的，因此OEC的功能对人类健康至关重要。拟议的研究将提供关于OEC如何产生氧气的新信息。PSII的最新3.5英寸晶体结构提供了OEC的第一个结构模型。所揭示的几何形状的OEC符合很好的水裂解机制，由这个小组，其中，亲核钙结合水攻击的氧的Mn（V）=O物种的O？O键形成步骤。从新的结构，OEC将其特征在于使用PSII和生物无机锰模型化学的生物物理和计算研究的组合。长期目标是在分子水平上了解OEC的结构和组装、水氧化的机制、PSII的电子转移特性以及水氧化过程中发生的破坏性副反应。该项目分为两个具体目标：（1）表征OEC的结构和功能，以及（2）使用Mn配位络合物来帮助解释OEC的生物物理研究。在目标1中，提出了研究通过使用阳离子和/或离子取代的PSII来表征Ca在OEC中的功能，通过研究CP 43-Arg 357突变体来测试CP 43-Arg 357在O-O键形成步骤中作为催化碱起作用的提议，并使用计算建模来深入了解OEC的结构和功能。在目标2中，Mn配位络合物将用于通过测量18-O-标记的水与模拟OEC的结构性质的一系列Mn配位络合物中的水/氢氧化物/μ-氧物种的交换来深入了解底物沃茨如何结合在OEC中。除了提供PSII的水氧化化学的更清晰的图片，拟议的研究将提供洞察其他金属酶的机制，对人类健康至关重要，如那些使用氧气或过氧化氢作为底物。

DESCRIPTION (provided by applicant): Photosystem II (PSII) is a membrane protein complex that uses light to catalyze water oxidation and quinone reduction. The oxygen-evolving complex (OEC) of PSII is the source of the atmospheric oxygen that we breathe. Because atmospheric oxygen is essential to sustain all aerobic life on Earth, the function of the OEC is of major importance to human health. The proposed studies will provide new information on how oxygen is produced by the OEC. The recent 3.5 ¿ crystal structure of PSII provides the first structural model of the OEC. The revealed geometry of the OEC fits well with the water-splitting mechanism advanced by this group in which, a nucleophilic Ca-bound water attacks the oxygen of a Mn(V)=O species in the O?O bond- forming step. Following from the new structure, the OEC will be characterized by using a combination of biophysical and computational studies of PSII and bioinorganic Mn model chemistry. The long-term objectives are to develop an understanding at the molecular level of the structure and assembly of the OEC, the mechanism of water oxidation, the electron-transfer properties of PSII and the damaging side reactions that occur in the process of water oxidation. This project is divided into two specific aims: (1) to characterize the structure and function of the OEC, and (2) to use Mn coordination complexes to aid in the interpretation of biophysical studies of the OEC. In aim 1, studies are proposed to characterize the function of Ca in the OEC by using cation- and/or an ion-substituted PSII, to test the proposal that CP43-Arg357 functions as a catalytic base in the O-O bond-forming step by study of CP43-Arg357 mutants, and to use computational modeling to gain insight into the structure and function of the OEC. In aim 2, Mn coordination complexes will be used to gain insight into how the substrate waters are bound in the OEC by measuring the exchange of 18-O-labeled water with water/hydroxide/mu-oxo species in a series of Mn coordination complexes that model the structural properties of the OEC. In addition to providing a clearer picture of the water-oxidation chemistry of PSII, the proposed studies will provide insight into the mechanisms of other metalloenzymes that are essential to human health such as those that use oxygen or hydrogen peroxide as a substrate.