Polynuclear iron complexes as functional mimics of the nitrogenase FeMo-cofactor

多核固氮酶辅因子的功能模型 氮进入生物圈是所有生物过程的限速步骤，因此也是生命本身的限速步骤。 氮素还原发生在称为固氮酶的多核金属酶上。它的反应中心 含钼酶由半胱氨酸连接的MoFe7S7辅因子(FeMoco)组成，其中二氮 凝视发生了。尽管关于辅因子的结构信息很好，但关于底物的许多问题 在周转期间，辅因子的摄取和整体化学作用仍然存在。具体地说，氧化还原灵活性 Mo指出它可能参与底物激活，这一点已经通过功能模型研究进行了审查。 然而，点突变研究和理论模型表明，FeMoco TO是一个多核Fe面 参与底物活化。人工合成的结构类似物被用来复制辅因子 组成并阐明模仿辅因子的结构细节。然而，不存在任何合成模型 将允许探测固氮酶底物和多核反应部位之间的相互作用 这使人想起在联邦经货管理处/联邦对外经济和社会事务部/联邦选举委员会中在场的人。使用我们实验室开发的合成方法来 可靠地合成多核团簇，拟议的研究的目标是在功能和结构上都 模拟FeMoco的活性中心。聚酰胺和聚酰胺/硫化物配体体系允许分离和研究 定义明确的三核和六核铁络合物。分子三铁单元将允许系统检查 只含铁的固氮酶底物的反应化学性质。此外，双分子 三铁单元的偶联将允许合成和表征辅因子的各种结构模拟物 具有不同的间隙原子成分(如C，N，O，S)。拟议的研究将允许进行测试 关于固氮酶底物与普遍存在的多核反应中心相互作用的几个假说 在天然酶中：底物如何结合；氧化还原如何分布在整个簇状反应部位；如何 做表面氢化物栅极氮气或衬底结合；我们能验证机械建议为 酶通过观察非生物模型？模拟固氮酶的合成类似物的可行性 活性将通过分析合成簇合物对固氮酶底物的反应性来探测。

Project Summary: Functional models of the polynuclear nitrogen-fixing enzyme cofactors Nitrogen entry into the biosphere is the rate-limiting step for all biological processes, and therefore, life itself. Dinitrogen reduction occurs at polynuclear metalloenzymes called nitrogenase. The reaction center of the Molybdenum-containing enzyme consists of a cysteine ligated MoFe7S7 cofactor (FeMoco) where dinitrogen fixation takes place. Despite good structural information about the cofactor, many questions regarding substrate uptake and the overall chemical action of the cofactor during turnover remain. Specifically, the redox flexibility of Mo point to its likely involvement in substrate activation, which has been vetted by functional model studies. However, site-mutagenesis studies and theoretical models indicate a polynuclear Fe-face of FeMoco to participate in substrate activation. Synthetic structural analogues have been fashioned to reproduce the cofactor composition and elucidate structural details that mimic the cofactor. However, no synthetic models exist that would permit probing of the interaction between nitrogenase substrates and a polynuclear reaction site reminiscent of those present in FeMo/FeV/Feco. Using synthetic methodology developed in our laboratories to reliably synthesize polynuclear clusters, the goal of the proposed research is to both functionally and structurally model the active site of FeMoco. Polyamide and polyamide/sulfide ligand systems permit the isolation and study of well-defined tri- and hexanuclear iron complexes. The molecular tri-iron units will allow systematic examination of the reaction chemistry of nitrogenase substrates with an iron-only reaction site. Furthermore, bimolecular coupling of tri-iron units will permit the synthesis and characterization of various structural mimics of the cofactor featuring different interstitial atom components (e.g., C, N, O, S). The proposed research will permit the testing of several hypotheses concerning interaction of nitrogenase substrates with polynuclear reaction sites prevalent in the native enzyme: how do substrates bind; how is redox distributed throughout the cluster reaction site; how do surface hydrides gate dinitrogen or substrate binding; can we authenticate mechanistic proposal for the enzyme by observation of abiological models? The viability of the synthetic analogues to mimic nitrogenase activity will be probed by profiling the reactivity of the synthetic clusters towards nitrogenase substrates.