A bound reaction intermediate sheds light on the mechanism of nitrogenase
A bound reaction intermediate sheds light on the mechanism of nitrogenase
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DOI：
10.1126/science.aar2765
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发表时间：
2018-03-30
期刊：
影响因子：
56.9
通讯作者：
Einsle, Oliver
中科院分区：
文献类型：
--
作者：
Sippel, Daniel;Rohde, Michael;Einsle, Oliver
固氮酶对N-2的还原作用发生在一种通常也含有钼或钒的有机金属铁辅因子上。辅因子良好的静息状态不结合底物，因此它的作用方式仍然是个谜。最近发现一氧化碳可以取代一种桥接硫化物，但机理上的相关性尚不清楚。在这里，我们报告了钒固氮酶的结构分析，它带有一个结合的中间体，被解释为Mu(2)-桥联的质子化氮，这意味着底物与辅因子结合的位置和方式。结合会导致氨基酸谷氨酰胺176的翻转，这会使配体氢键结合，并为取代的硫化物创造一个固定位置。中间体可能代表Thorneley-Lowe模型的E-6或E-7状态，并为催化循环的其余部分提供线索。
Reduction of N-2 by nitrogenases occurs at an organometallic iron cofactor that commonly also contains either molybdenum or vanadium. The well-characterized resting state of the cofactor does not bind substrate, so its mode of action remains enigmatic. Carbon monoxide was recently found to replace a bridging sulfide, but the mechanistic relevance was unclear. Here we report the structural analysis of vanadium nitrogenase with a bound intermediate, interpreted as a mu(2)-bridging, protonated nitrogen that implies the site and mode of substrate binding to the cofactor. Binding results in a flip of amino acid glutamine 176, which hydrogen-bonds the ligand and creates a holding position for the displaced sulfide. The intermediate likely represents state E-6 or E-7 of the Thorneley-Lowe model and provides clues to the remainder of the catalytic cycle.