FTIR Studies of Photosynthetic Oxygen Evolution

光合产氧的 FTIR 研究

• 批准号: 7018763
• 负责人: RICHARD J DEBUS
• 金额: $ 25.08万
• 依托单位: UNIVERSITY OF CALIFORNIA RIVERSIDE
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-03 至 2010-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7018763
• 关键词: Rhodospirillales; active sites; bacterial proteins; biochemical evolution; electron transport; infrared spectrometry; interferometry; ions; manganese; oxidation; oxygen; photosynthesis; photosynthetic reaction centers; photosystem; protein sequence; protein structure function; protonation; radiotracer; site directed mutagenesis; water

DESCRIPTION (provided by applicant): The project's overall goal is to elucidate the molecular mechanism of photosynthetic oxygen evolution. This process takes place in Photosystem II and is the source of nearly all atmospheric oxygen. The catalytic site contains a (Mn)4-Ca cluster that interacts with a redox-active tyrosine residue known as YZ. The YZ( radical extracts electrons and protons from the (Mn)4-Ca cluster, leading to the oxidation of water and the release of oxygen. The project's primary goal is to characterize the structural changes that accompany the oxidation of the (Mn)4-Ca cluster during the individual steps of the catalytic cycle. This information is crucial to understanding the mechanism of oxygen evolution and will complement the information that is being obtained from X-ray crystallography. The primary investigative tool will be Fourier transform infrared (FTIR) difference spectroscopy. The project's specific aims are: (1) To identify the specific Mn ion(s) that undergo oxidation during the individual steps in the catalytic cycle; (2) To identify the amino acid residues that serve as the critical bases that facilitate the proton-coupled oxidations of the (Mn)4-Ca cluster during the catalytic cycle; (3) To characterize the final intermediate of the oxygen formation reaction, an intermediate that can be trapped by increasing the ambient oxygen pressure; (4) To employ modified bacterial reaction centers as model systems for characterizing changes that occur in the environment of a ligated metal ion in response to its oxidation; (5) To employ near-infrared excitation resonance Raman spectroscopy as an additional tool for characterizing the environment of the (Mn)4-Ca cluster. In addition to providing fundamental insight into the mechanism of photosynthetic oxygen evolution, the project will provide insight into the mechanisms of metalloradical enzymes and enzymes whose mechanisms involve proton-coupled electron transfer (PCET) reactions. Such enzymes catalyze biological energy transduction in mitochondria. Elucidating the catalytic mechanisms of these enzymes is essential for understanding the molecular basis of mitochondrial diseases and aging. Photosystem II is both an excellent example of a metalloradical enzyme and a unique laboratory for studying proton-coupled electron transfer reactions. Its advantages derive from its ability to be stepped through its catalytic cycle with single flashes of light, thereby facilitating kinetic studies of reaction cycle intermediates with high time resolution.

描述（由申请人提供）：该项目的总体目标是阐明光合放氧的分子机制。这个过程发生在光系统 II 中，并且是几乎所有大气氧气的来源。催化位点包含 (Mn)4-Ca 簇，该簇与氧化还原活性酪氨酸残基（称为 YZ）相互作用。 YZ( 自由基从 (Mn)4-Ca 簇中提取电子和质子，导致水氧化并释放氧气。该项目的主要目标是表征伴随 (Mn)4 氧化的结构变化-Ca 簇在催化循环的各个步骤中对于理解氧气析出的机制至关重要，并将补充从 X 射线晶体学中获得的信息。不同之处该项目的具体目标是：（1）识别在催化循环的各个步骤中经历氧化的特定锰离子；（2）识别作为促进氧化反应的关键碱基的氨基酸残基。 (Mn)4-Ca簇在催化循环过程中的质子耦合氧化；(3) 表征氧形成反应的最终中间体，该中间体可以通过增加环境氧气压力来捕获； (4) 采用改良的细菌反应中心作为模型系统来表征连接金属离子的环境中响应其氧化而发生的变化； (5) 采用近红外激发共振拉曼光谱作为表征 (Mn)4-Ca 团簇环境的附加工具。除了提供对光合产氧机制的基本见解外，该项目还将深入了解金属自由基酶和其机制涉及质子耦合电子转移（PCET）反应的酶的机制。此类酶催化线粒体中的生物能量转导。阐明这些酶的催化机制对于理解线粒体疾病和衰老的分子基础至关重要。 Photosystem II 既是金属自由基酶的绝佳范例，也是研究质子耦合电子转移反应的独特实验室。其优势源自其能够通过单次闪光逐步完成催化循环，从而促进以高时间分辨率进行反应循环中间体的动力学研究。