Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester, M1 7DN, UK.
Department of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
Chemistry. 2021 Jan 21;27(5):1795-1809. doi: 10.1002/chem.202004019. Epub 2020 Dec 30.
The nonheme iron enzyme OrfP reacts with l-Arg selectively to form the 3R,4R-dihydroxyarginine product, which in mammals can inhibit the nitric oxide synthase enzymes involved in blood pressure control. To understand the mechanisms of dioxygen activation of l-Arg by OrfP and how it enables two sequential oxidation cycles on the same substrate, we performed a density functional theory study on a large active site cluster model. We show that substrate binding and positioning in the active site guides a highly selective reaction through C -H hydrogen atom abstraction. This happens despite the fact that the C -H and C -H bond strengths of l-Arg are very similar. Electronic differences in the two hydrogen atom abstraction pathways drive the reaction with an initial C -H activation to a low-energy σ-pathway, while substrate positioning destabilizes the C -H abstraction and sends it over the higher-lying π-pathway. We show that substrate and monohydroxylated products are strongly bound in the substrate binding pocket and hence product release is difficult and consequently its lifetime will be long enough to trigger a second oxygenation cycle.
非血红素铁酶 OrfP 选择性地与 l-Arg 反应生成 3R,4R-二羟基精氨酸产物，该产物在哺乳动物中可以抑制参与血压控制的一氧化氮合酶。为了理解 OrfP 使 l-Arg 双氧化的氧分子活化机制，以及它如何使同一底物上进行两个连续的氧化循环，我们对一个大的活性位点簇模型进行了密度泛函理论研究。我们表明，底物在活性位点中的结合和定位通过 C -H 氢键的氢原子提取引导高度选择性的反应。尽管 l-Arg 的 C -H 和 C -H 键强度非常相似，但这一事实发生了。两种氢原子提取途径的电子差异使得反应以初始 C -H 活化进入低能 σ-途径，而底物定位使 C -H 提取失稳，并使其越过较高的 π-途径。我们表明，底物和单羟化产物在底物结合口袋中被强烈结合，因此产物释放困难，其寿命将足够长，足以引发第二个氧化循环。
