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

描述(由申请人提供)：多核固氮酶的功能模型辅因氮进入生物圈是所有生物过程的限速步骤，因此，生命本身。氮素还原发生在称为固氮酶的多核金属酶上。含钼酶的反应中心由半胱氨酸连接的MoFe7S7辅因子(FeMoco)组成，在那里进行氮固定。尽管关于辅因子的结构信息很好，但许多关于底物摄取和辅因子在周转期间的整体化学作用的问题仍然存在。具体地说，钼的氧化还原灵活性表明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，定点突变研究和理论模型表明，FeMoco的多核铁面参与了底物的激活。人工合成的结构类似物被用来复制辅因子的组成，并阐明模仿辅因子的结构细节。然而，没有合成模型可以允许探测固氮酶底物和多核反应部位之间的相互作用，这让人想起FeMoco中存在的那些。利用我们实验室开发的合成方法可靠地合成多核簇，拟议的研究目标是从功能和结构上模拟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地检查具有仅铁反应部位的固氮酶底物的反应化学。此外，三铁单元的双分子耦合将允许合成和表征具有不同间隙原子成分的辅因子的各种结构模拟。拟议的研究将允许测试几个关于固氮酶底物与FeMoco中普遍存在的多核反应中心相互作用的假设。

DESCRIPTION (provided by applicant): 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 FeMoco. 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. The proposed research will permit the testing of several hypotheses concerning interaction of nitrogenase substrates with polynuclear reaction sites prevalent in FeMoco.