Čorić Ilija, Mercado Brandon Q, Bill Eckhard, Vinyard David J, Holland Patrick L
Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, USA.
Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.
Nature. 2015 Oct 1;526(7571):96-9. doi: 10.1038/nature15246. Epub 2015 Sep 23.
Nitrogenases are the enzymes by which certain microorganisms convert atmospheric dinitrogen (N2) to ammonia, thereby providing essential nitrogen atoms for higher organisms. The most common nitrogenases reduce atmospheric N2 at the FeMo cofactor, a sulfur-rich iron-molybdenum cluster (FeMoco). The central iron sites that are coordinated to sulfur and carbon atoms in FeMoco have been proposed to be the substrate binding sites, on the basis of kinetic and spectroscopic studies. In the resting state, the central iron sites each have bonds to three sulfur atoms and one carbon atom. Addition of electrons to the resting state causes the FeMoco to react with N2, but the geometry and bonding environment of N2-bound species remain unknown. Here we describe a synthetic complex with a sulfur-rich coordination sphere that, upon reduction, breaks an Fe-S bond and binds N2. The product is the first synthetic Fe-N2 complex in which iron has bonds to sulfur and carbon atoms, providing a model for N2 coordination in the FeMoco. Our results demonstrate that breaking an Fe-S bond is a chemically reasonable route to N2 binding in the FeMoco, and show structural and spectroscopic details for weakened N2 on a sulfur-rich iron site.
固氮酶是某些微生物将大气中的二氮（N₂）转化为氨的酶，从而为高等生物提供必需的氮原子。最常见的固氮酶在铁钼辅因子（一种富含硫的铁钼簇，FeMoco）处还原大气中的N₂。基于动力学和光谱学研究，有人提出在FeMoco中与硫和碳原子配位的中心铁位点是底物结合位点。在静止状态下，中心铁位点各自与三个硫原子和一个碳原子形成键。向静止状态添加电子会使FeMoco与N₂反应，但与N₂结合的物种的几何形状和键合环境仍然未知。在这里，我们描述了一种具有富含硫的配位球的合成配合物，该配合物在还原时会断裂Fe-S键并结合N₂。该产物是第一个铁与硫和碳原子形成键的合成Fe-N₂配合物，为FeMoco中的N₂配位提供了模型。我们的结果表明，断裂Fe-S键是FeMoco中N₂结合的化学合理途径，并展示了富含硫的铁位点上减弱的N₂的结构和光谱细节。
