Nitriles are uncommon in nature and are typically constructed from oximes through the oxidative decarboxylation of amino acid substrates or from the derivatization of carboxylic acids. Here we report a third nitrile biosynthesis strategy featuring the cyanobacterial nitrile synthase AetD. During the biosynthesis of the eagle-killing neurotoxin, aetokthonotoxin, AetD transforms the 2-aminopropionate portion of 5,7-dibromo-l-tryptophan to a nitrile. Employing a combination of structural, biochemical and biophysical techniques, we characterized AetD as a non-haem diiron enzyme that belongs to the emerging haem-oxygenase-like dimetal oxidase superfamily. High-resolution crystal structures of AetD together with the identification of catalytically relevant products provide mechanistic insights into how AetD affords this unique transformation, which we propose proceeds via an aziridine intermediate. Our work presents a unique template for nitrile biogenesis and portrays a substrate binding and metallocofactor assembly mechanism that may be shared among other haem-oxygenase-like dimetal oxidase enzymes.

腈在自然界中并不常见，通常由肟类化合物通过氨基酸底物的氧化脱羧或羧酸的衍生化构建而成。在这里，我们报道了第三种丁腈生物合成策略，其特点是蓝藻丁腈合酶 AetD。在杀鹰神经毒素 aetokthonotoxin 的生物合成过程中，AetD 将 5,7-二溴-l-色氨酸的 2-氨基丙酸部分转化为腈。采用结构、生化和生物物理技术的组合，我们将 AetD 表征为一种非血红素二铁酶，属于新兴的血红素加氧酶样双金属氧化酶超家族。AetD 的高分辨率晶体结构以及催化相关产物的鉴定为 AetD 如何提供这种独特的转变提供了机理见解，我们建议通过氮丙啶中间体进行。我们的工作提出了一种独特的丁腈生物发生模板，并描绘了可能与其他血红素加氧酶样二金属氧化酶共享的底物结合和金属因子组装机制。