Department of Physiology and Biophysics , Albert Einstein College of Medicine , Bronx , New York 10461 , United States.
J Am Chem Soc. 2018 Jul 11;140(27):8518-8525. doi: 10.1021/jacs.8b03691. Epub 2018 Jun 27.
Human indoleamine 2,3-dioxygenase 1 (hIDO1) and tryptophan dioxygenase (hTDO) catalyze the same dioxygenation reaction of Trp to generate N-formyl kynurenine (NFK). They share high structural similarity, especially in the active site. However, hIDO1 possesses a unique inhibitory substrate binding site (Si) that is absent in hTDO. In addition, in hIDO1, the indoleamine group of the substrate Trp is H-bonded to S167 through a bridging water, while that in hTDO is directly H-bonded to H76. Here we show that Trp binding to the Si site or the mutation of S167 to histidine in hIDO1 retards its turnover activity and that the inhibited activity can be rescued by an effector, 3-indole ethanol (IDE). Kinetic studies reveal that the inhibited activity introduced by Trp binding to the Si site is a result of retarded recombination of the ferryl moiety with Trp epoxide to form NFK and that IDE reverses the effect by preventing Trp from binding to the Si site. In contrast, the abolished activity induced by the S167H mutation is primarily a result of ∼5000-fold reduction in the O binding rate constant, possibly due to the blockage of a ligand delivery tunnel, and that IDE binding to the Si site reverses the effect by reopening the tunnel. The data offer new insights into structure-based design of hIDO1-selective inhibitors.
人吲哚胺 2,3-双加氧酶 1（hIDO1）和色氨酸双加氧酶（hTDO）催化色氨酸相同的双氧化反应，生成 N-甲酰犬尿氨酸（NFK）。它们具有高度的结构相似性，特别是在活性部位。然而，hIDO1 具有独特的抑制性底物结合位点（Si），而 hTDO 中则不存在。此外，在 hIDO1 中，底物色氨酸的吲哚基团通过桥接水与 S167 形成氢键，而在 hTDO 中则直接与 H76 形成氢键。在这里，我们表明色氨酸与 Si 结合或 hIDO1 中 S167 突变为组氨酸会降低其周转率活性，而效应物 3-吲哚乙醇（IDE）可以挽救被抑制的活性。动力学研究表明，色氨酸与 Si 结合所引入的抑制活性是由于 ferryl 部分与色氨酸环氧化物重新结合形成 NFK 的速度减慢所致，而 IDE 通过阻止色氨酸与 Si 结合来逆转这种效应。相比之下，S167H 突变引起的活性丧失主要是由于 O 结合速率常数降低了约 5000 倍，可能是由于配体输送隧道受阻所致，而 IDE 与 Si 结合通过重新打开隧道来逆转这种效应。这些数据为基于结构的 hIDO1 选择性抑制剂设计提供了新的见解。
