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

多核固氮酶辅助因子的功能模型 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。 二氮的还原发生在多核金属酶，称为固氮酶。的反应中心。 含钼酶由半胱氨酸连接的MoFe 7S 7辅因子（FeMoco）组成，其中二氮 固定发生。尽管有关于辅因子的良好结构信息，但关于底物的许多问题 在周转期间，辅因子的摄取和总体化学作用仍然存在。具体而言， Mo指出它可能参与底物活化，这已经通过功能模型研究进行了验证。 然而，位点诱变研究和理论模型表明FeMoco的多核Fe-面， 参与底物活化。合成的结构类似物已被改造，以复制辅因子 组成和阐明模拟辅因子的结构细节。然而，没有合成模型存在， 将允许探测固氮酶底物和多核反应位点之间的相互作用 使人想起FeMo/FeV/Feco中存在的那些。使用我们实验室开发的合成方法， 可靠地合成多核簇，拟议研究的目标是功能和结构 模拟FeMoco的活性位点。聚酰胺和聚酰胺/硫化物配体系统允许分离和研究 明确定义的三核和六核铁络合物。分子三铁单位将允许系统检查 固氮酶底物的反应化学与铁唯一的反应位点。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 其特征在于不同的间隙原子组分（例如，C、N、O、S）。拟议中的研究将允许测试 关于固氮酶底物与普遍存在的多核反应位点相互作用的几种假说 在天然酶中：底物如何结合;氧化还原如何分布在整个簇反应位点;如何 做表面修饰的二氮或底物结合;我们可以验证的机制建议， 通过观察非生物学模型的酶？合成类似物模拟固氮酶的可行性 通过分析合成簇对固氮酶底物的反应性来探测活性。

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.