Mechanism of Oxidative Ring-closure as Part of the Hygromycin Biosynthesis Step by a Nonheme Iron Dioxygenase
Mechanism of Oxidative Ring-closure as Part of the Hygromycin Biosynthesis Step by a Nonheme Iron Dioxygenase
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DOI：
10.1002/cctc.202100393
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发表时间：
2021-05-19
期刊：
影响因子：
4.5
通讯作者：
de Visser, Sam P.
中科院分区：
文献类型：
--
作者：
Ali, Hafiz Saqib;Henchman, Richard H.;de Visser, Sam P.
非血红素铁双加氧酶催化生物系统的重要反应，包括抗生素的生物合成。一种这样的酶，即潮霉素生物合成酶（HygX），进行氧化闭环反应以形成原酸酯产物，这是药物合成和生物技术的相关反应步骤。为了理解HygX中氧化闭环形成原酸酯产物的选择性反应机理，我们研究了其导致各种产物的催化反应机理。建立了大活性中心簇模型，计算了底物活化的各种途径。这项工作确定了一种高价铁（IV）-氧代物种在五重自旋状态作为活性氧化剂，选择性地提取质子的醇基的基板，这是其次是从叔C-H基团和快速电子转移的氢原子提取。后者形成的双自由基中间体重排形成去饱和的闭环产物。计算表明，活性位点赖氨酸残基捐赠正电荷的金属氧代基团，并引导反应的化学选择性去饱和途径。
Nonheme iron dioxygenases catalyze vital reactions for biosystems including the biosynthesis of antibiotics. One such enzyme, namely the hygromycin biosynthesis enzyme (HygX), performs an oxidative ring-closure reaction to form an ortho-ester product, which is a relevant reaction step for drug synthesis and biotechnology. To understand the selective reaction mechanism of oxidative ring-closure to form ortho-ester products in HygX, we investigated its catalytic reaction mechanism leading to various products. Large active site cluster models were set-up and various pathways for substrate activation have been calculated. The work identifies a high-valent iron(IV)-oxo species in the quintet spin state as the active oxidant that selectively abstracts a proton of an alcohol group of the substrate, which is followed by a hydrogen atom abstraction from a tertiary C-H group and rapid electron transfer. The latter-formed biradical intermediate rearranges to form the desaturated ring-closed product. The calculations show that an active site Lys residue donates positive charge to the metal-oxo group and guides the reaction to a chemoselective desaturation pathway.