Biophysical and Bioinorganic Studies of Oxygen Evolution

描述(申请人提供)：光系统II(PSII)是一种膜蛋白复合体，它用光催化水氧化和苯二酚还原。PSII的放氧复合体(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最新的3.5°晶体结构提供了OEC的第一个结构模型。OEC的几何构型与该小组提出的水的裂解机理很好地吻合，在O？O成键步骤中，亲核的钙结合水攻击了Mn(V)=O物种的氧。在新的结构之后，OEC将通过结合PSII的生物物理和计算研究以及生物无机Mn模型化学来表征。长期目标是在分子水平上了解OEC的结构和组装、水氧化的机理、PSII的电子转移特性以及在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；(2)使用锰配位络合物帮助解释OEC的生物物理研究。在目标1中，通过阳离子和/或离子取代的PSII来表征钙在OEC中的功能，通过对CP43-Arg357突变体的研究来检验CP43-Arg357在O-O键形成步骤中作为催化碱基的观点，并利用计算模拟来深入了解OEC的结构和功能。在目标2中，将使用锰配位络合物通过测量18-O标记的水与一系列锰配位络合物中的水/氢氧化物/钼氧物种的交换来深入了解底物水是如何结合在OEC中的，这些络合物模拟了OEC的结构特性。除了提供PSII水氧化化学的更清晰的图景外，拟议的研究还将提供对人类健康必不可少的其他金属酶的机制的洞察，例如那些使用氧或过氧化氢作为底物的金属酶。

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.