Low-Coordinate Synthetic Models for Nitrogenase Activity

固氮酶活性的低坐标合成模型

• 批准号: 9312826
• 负责人: PATRICK L HOLLAND
• 金额: $ 32.85万
• 依托单位: YALE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-04-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9312826
• 关键词: Active Sites; Air; Amaze; Ammonia; Anabolism; Binding; Biochemical Reaction; Biochemistry; Bioinorganic Chemistry; Chemicals; Chemistry; Complex; Crystallization; Crystallography; Electrochemistry; Electron Nuclear Double Resonance; Electron Transport; Enzymes; Iron; Kinetics; Life; Ligands; Literature; Magnetic Resonance; Metals; Modeling; Molybdoferredoxin; Nitrogen; Nitrogen Fixation; Nitrogenase; Periodicity; Planet Earth; Play; Reaction; Research; Roentgen Rays; Role; Site; Spectrum Analysis; Structure; Sulfides; Sulfur; Support Groups; Testing; Transcend; Translating; absorption; analog; base; biological systems; cofactor; foot; functional group; metalloenzyme; novel; spectroscopic data

In nitrogenases, iron-sulfur (FeS) clusters transcend their usual role as electron transfer sites, by performing the difficult multielectron reduction of N2 to NH3. Nitrogenase thus demonstrates the amazing catalytic ability of iron-sulfur clusters in biological systems. The site of N2 reduction in nitrogenase is an FeS cluster called the iron-molybdenum cofactor (FeMoco), which is the only example of a metal-carbide in biological chemistry. This carbide may be inserted by way of cluster-CH3, -CH2, and -CH intermediates, which are also unprecedented in FeS cluster chemistry. This enzyme is currently postulated to use species unknown to chemists: organometallic FeS clusters, FeS clusters with carbides, FeS clusters with hydrides, and FeS clusters bound to N2. Because of the lack of precedents, there is an urgent need to build up the experimental basis for evaluating the literature-proposed mechanisms for FeMoco biosynthesis and activity. Our guiding hypothesis is that the role of carbide in FeMoco is to hold and release transient low-coordinate iron sites, which can form bridging Fe-N2 and Fe-H intermediates during the catalytic mechanism. This will be tested using the synthetic analogue strategy, which is well-precedented in bioinorganic chemistry. Synthetic FeS clusters with N2, H, and C groups on the cluster can show the feasibility of the proposed functional groups on iron-sulfur clusters, establish the spectroscopic signatures of specific functional groups, and show whether their reactions are consistent with the models for FeMoco mechanism. Similarly, cluster-bound CH2, CH, and C groups would help to determine the feasibility of potential steps in FeMoco biosynthesis. In the proposed research, we will synthesize and study synthetic FeS compounds with each of the following novel functionalities: (1) unsaturated iron-sulfur clusters that bind nitrogenase substrates, (2) iron-sulfide- hydride clusters, and (3) iron clusters with CH2/CH/C bridges. We will use bulky supporting groups to stabilize reactive species, to facilitate crystallization, and to enable systematic study of their reactions. Crystallography, kinetic studies, electrochemistry, and reactivity will be used to understand the binding and reduction of N2 and other nitrogenase substrates. This in turn shows what types of reactions are reasonable to expect with the FeMoco. The structurally-defined synthetic complexes will also be evaluated by magnetic resonance, infrared, Raman, Mössbauer, and X-ray absorption spectroscopies, which will serve to "translate" the known spectroscopic data for nitrogenase into reasonable structural conclusions. Nitrogenase is one of the strangest metalloenzymes, because of its strongly reducing multielectron reduction, the cofactor structure with a carbide, and the ability to interact with usually-inert N2. Understanding its mechanism thus requires new discoveries about the fundamental chemistry of FeS clusters. This project aims to provide the chemical precedents that are needed to put nitrogenase mechanism on a firm footing.

在固氮酶中，铁硫 (FeS) 簇超越了其通常作为电子转移位点的作用，通过执行 N2 到 NH3 的困难的多电子还原证明了固氮酶惊人的催化能力。 生物系统中的铁硫簇，固氮酶中 N2 还原的位点是 FeS 簇，称为 FeS 簇。 铁钼辅因子（FeMoco），这是生物化学中金属碳化物的唯一例子。 碳化物可以通过簇状-CH3、-CH2和-CH中间体的方式插入，这也是前所未有的 目前推测该酶使用化学家未知的物种： 有机金属 FeS 团簇、含有碳化物的 FeS 团簇、含有氢化物的 FeS 团簇以及与 N2. 由于缺乏先例，迫切需要建立评估的实验基础。 文献提出的 FeMoco 生物合成和活性机制。 我们的指导性假设是，FeMoco 中碳化物的作用是保持和释放瞬态低配位 铁位点，在催化机制中可以形成桥接 Fe-N2 和 Fe-H 中间体。 使用合成类似物策略进行测试，这在生物无机化学中是有先例的。 FeS簇上含有N2、H和C基团，可以显示所提出的官能团的可行性 在铁硫簇上，建立特定官能团的光谱特征，并显示是否 它们的反应与 FeMoco 机制的模型一致，类似地，团簇结合的 CH2、CH 和 C。 小组将有助于确定 FeMoco 生物合成中潜在步骤的可行性。 在拟议的研究中，我们将合成并研究具有以下各项的合成 FeS 化合物 新功能：（1）结合固氮酶底物的不饱和铁硫簇，（2）铁硫化物 氢化物簇，以及（3）具有CH2/CH/C桥的铁簇我们将使用庞大的支撑基团来稳定。 活性物质，以促进结晶，并能够系统地研究它们的反应， 动力学研究、电化学和反应性将用于了解 N2 和 N2 的结合和还原 这反过来又显示了可以合理预期的反应类型。 FeMoco 也将通过磁共振、红外、 拉曼、穆斯堡尔和 X 射线吸收光谱，这将有助于“翻译”已知的 将固氮酶的光谱数据转化为合理的结构结论。 固氮酶是最奇怪的金属酶之一，因为它具有强还原性多电子 还原、碳化物的辅助因子结构以及与通常惰性的 N2 相互作用的能力。 因此，其机制需要有关 FeS 簇的基本化学的新发现。 旨在提供使固氮酶机制站稳脚跟所需的化学先例。