What Determines the Selectivity of Arginine Dihydroxylation by the Nonheme Iron Enzyme OrfP?
What Determines the Selectivity of Arginine Dihydroxylation by the Nonheme Iron Enzyme OrfP?
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DOI：
10.1002/chem.202004019
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发表时间：
2020-12-30
影响因子：
4.3
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.
非血红素铁酶 OrfP 选择性地与 l-精氨酸反应，形成 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。为了了解 OrfP 对 l-Arg 的双氧活化机制以及它如何在同一底物上实现两个连续的氧化循环，我们对大型活性位点簇模型进行了密度泛函理论研究。我们表明，底物在活性位点的结合和定位通过 C-3-H 氢原子的抽象引导高度选择性的反应。尽管 L-Arg 的 C-3-H 和 C-4-H 键强度非常相似，但这种情况还是发生。两个氢原子提取途径中的电子差异将初始 C-3-H 激活的反应驱动到低能 (5)sigma 途径，而底物定位会破坏 C-4-H 提取的稳定性，并将其发送到位置较高的 (5)pi 途径。我们表明，底物和单羟基化产物在底物结合袋中牢固结合，因此产物释放很困难，因此其寿命将足够长以触发第二个氧合循环。
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-3-H hydrogen atom abstraction. This happens despite the fact that the C-3-H and C-4-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-3-H activation to a low-energy (5)sigma-pathway, while substrate positioning destabilizes the C-4-H abstraction and sends it over the higher-lying (5)pi-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.