Lee Chi Chung, Kang Wonchull, Jasniewski Andrew J, Stiebritz Martin T, Tanifuji Kazuki, Ribbe Markus W, Hu Yilin
Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900.
Department of Chemistry, College of Natural Sciences, Soongsil University, Seoul 06978, Republic of Korea.
Nat Catal. 2022 May;5(5):443-454. doi: 10.1038/s41929-022-00782-7. Epub 2022 May 16.
The Mo-nitrogenase catalyses the ambient reduction of N to NH at the M-cluster, a complex cofactor that comprises two metal-sulphur partial cubanes ligated by an interstitial carbide and three belt-sulphurs. A recent crystallographic study suggests binding of N via displacement of the belt-sulphur(s) of the M-cluster upon turnover. However, the direct proof of N binding and belt-sulphur mobilization during catalysis remains elusive. Here we show that N is captured on the M-cluster via electron- and sulphur-depletion, and that the N-captured state is catalytically competent in generating NH. Moreover, we demonstrate that product release only occurs when sulphite is supplied along with a reductant, that sulphite is inserted as sulphide into the belt-sulphur displaced positions, and that there is a dynamic in-and-out of the belt-sulphurs during catalysis. Together, these results establish the mobilization of the cofactor belt-sulphurs as a crucial, yet overlooked, mechanistic element of the nitrogenase reaction.
钼铁固氮酶在M簇上催化N向NH的常温还原反应，M簇是一种复杂的辅助因子，由两个通过间隙碳化物和三个带状硫连接的金属硫部分立方烷组成。最近的一项晶体学研究表明，在周转过程中，N通过取代M簇的带状硫而结合。然而，催化过程中N结合和带状硫移动的直接证据仍然难以捉摸。在这里，我们表明N通过电子和硫耗尽在M簇上捕获，并且捕获N的状态在催化生成NH方面具有活性。此外，我们证明只有当亚硫酸盐与还原剂一起供应时才会发生产物释放，亚硫酸盐作为硫化物插入到被取代的带状硫位置，并且在催化过程中带状硫存在动态的进出。这些结果共同确定了辅助因子带状硫的移动是固氮酶反应中一个关键但被忽视的机制要素。
