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.

在氮酶中，铁硫（FES）簇通过执行以电子转移位点的通常作用 N2的难度将NH3降低了困难。因此，氮酶证明了惊人的催化能力 生物系统中的铁硫簇。氮酶减少的位点是一个称为FES簇 铁 - 多胞果辅因子（FEMOCO），这是生物化学中金属碳化物的唯一例子。这 碳化物可以通过集群-CH3，-CH2和-CH中间体插入，这也是前所未有的 FES簇化学。目前，该酶使用化学家未知的物种： 有机FES簇，带碳化物的FES簇，带有氢化物的FES簇和FES簇结合 N2。由于缺乏先例，迫切需要建立评估的实验基础 股骨生物合成和活性的文献所述机制。 我们的指导假设是，碳化物在Femoco中的作用是保持和释放瞬态低坐标 铁位点可以在催化机制过程中形成桥接的Fe-N2和Fe-H中间体。这将是 使用合成模拟策略进行了测试，该策略在生物无机化学中是良好的。合成的 集群上的N2，H和C组的FES簇可以显示拟议的官能团的可行性 在铁硫簇上，建立特定官能团的光谱特征，并显示是否显示 它们的反应与Femoco机制的模型一致。同样，聚集的CH2，CH和C 小组将有助于确定股骨生物合成中潜在步骤的可行性。 在拟议的研究中，我们将与以下每种合成并研究合成FES化合物 新功能：（1）结合氮酶底物的不饱和铁硫簇，（2）铁硫化物 - 氢化物簇和（3）带有CH2/CH/C桥的铁簇。我们将使用笨重的辅助团体稳定 反应性物种，促进结晶，并能够系统地研究其反应。晶体学， 动力学研究，电化学和反应性将用于了解N2和 其他氮酶底物。这反过 Femoco。结构定义的合成复合物也将通过磁共振，红外， 拉曼，莫斯鲍尔和X射线抽象光谱镜像将“翻译”已知的 氮酶的光谱数据分为合理的结构结论。 氮酶是最奇怪的金属酶之一，因为它强烈降低了多电源 还原，具有碳化物的辅因子结构以及与intert n2相互作用的能力。理解 因此，它的机制需要有关FES簇的基本化学反应的新发现。这个项目 旨在提供将氮酶机制放在固件基础上所需的化学先例。