Expanding the Catalytic Repertoire of Heme-based Dioxygenases

项目总结 人色氨酸双加氧酶(HTDO)和吲哚胺2，3-双加氧酶1(HIDO1)是两种半蛋白 催化L-色氨酸(Trp)的双氧合反应生成N-甲酰犬尿氨酸。尽管它是 普遍认为电子和质子对血红素蛋白的氧活化至关重要， 双加氧酶是如此独特，它们催化色氨酸的氧化环裂解反应而不消耗 任何电子或质子。利用时间分辨共振拉曼光谱，结合QM/MM 通过模拟，我们建立了一种底物辅助机制来解释这种不寻常的化学 由双加氧酶催化。最近，我们发现，除了色氨酸的双氧合活性外， HTDO可结合活性部位的NAD(P)H，从而改变其用途，用于(I)血红素加氧酶(HO)反应， 将有活性的完整蛋白转化为无活性的脱辅基蛋白，(Ii)氧化反应，将O2还原为 和(Iii)过氧化物酶反应，将过氧化氢还原为水。尽管hTDO和hIDO1共享 一个共同的活性中心结构和催化色氨酸二加氧反应具有相同的机理，hIDO1 不显示HO活性，但保留了氧化酶和过氧化物酶活性。这些令人兴奋的新消息 这一发现扩大了以血红素为基础的双加氧酶的底物组合和催化体系。少校 这个项目的目标是破译决定这两种酶新酶活性的结构决定因素。 双加氧酶。这个项目的科学前提是对新的酶活性的理解 HTDO和hIDO1的研究将进一步加深我们对血红素氧化学的认识，并对它们的 生理功能，从而为疾病控制和预防提供指导。

PROJECT SUMMARY Human tryptophan dioxygenase (hTDO) and indoleamine 2, 3-dioxygenase 1 (hIDO1) are two hemeproteins that catalyze the dioxygenation reaction of L-tryptophan (Trp) to N-formyl kynurenine. Although it is generally believed that electrons and protons are crucial for oxygen activation by hemeproteins, the dioxygenases are so unique that they catalyze the oxidative ring cleavage reaction of Trp without consuming any electrons or protons. With time-resolved resonance Raman spectroscopy, combined with QM/MM simulations, we have established a substrate-assisted mechanism accounting for the unusual chemistry catalyzed by the dioxygenases. Recently, we discovered that, in addition to the Trp dioxygenation activity, hTDO can bind NAD(P)H in the active site, thereby repurposing it for (i) a heme oxygenase (HO) reaction, which converts the active holoprotein to the inactive apoprotein, (ii) an oxidase reaction, which reduces O2 to superoxide, and (iii) a peroxidase reaction, which reduces H2O2 to water. Although hTDO and hIDO1 share a common active site structure and catalyze the Trp dioxygenation reaction with the same mechanism, hIDO1 does not exhibit the HO activity, but it retains the oxidase and peroxidase activities. These exciting new findings expand the substrate portfolio and the catalytic repertoire of the heme-based dioxygenases. The major goal of this project is to decipher the structural determinants dictating the novel enzymatic activities of the two dioxygenases. The scientific premise of this project is that the comprehension of the new enzymatic activities of hTDO and hIDO1 will further our knowledge in heme oxygen chemistry and provide new insights into their physiological functions, thereby offering guidelines for disease control and prevention.