Molecular basis for catalysis and substrate-mediated cellular stabilization of human tryptophan 2,3-dioxygenase.
Molecular basis for catalysis and substrate-mediated cellular stabilization of human tryptophan 2,3-dioxygenase.
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DOI：
10.1038/srep35169
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发表时间：
2016-10-20
影响因子：
4.6
通讯作者：
Tong L
中科院分区：
文献类型：
--
作者：
Lewis-Ballester A;Forouhar F;Kim SM;Lew S;Wang Y;Karkashon S;Seetharaman J;Batabyal D;Chiang BY;Hussain M;Correia MA;Yeh SR;Tong L
色氨酸2，3-双加氧酶（TDO）和吲哚胺2，3-双加氧酶（IDO）在色氨酸代谢中起核心作用，并且参与许多细胞和疾病过程。在这里，我们报告的晶体结构的人TDO（hTDO）在一个三元复合物与底物L-色氨酸和O2和在一个二元复合物与产品N-甲酰犬尿氨酸（NFK），首次定义的结合模式的两个基板和该酶的产品。结构表明，双氧化反应是由O2直接攻击L-Trp吲哚环的C2原子引发的。该结构还揭示了L-Trp的外切结合位点，其位于距离活性位点约42 μ m处，并且由色氨酸营养缺陷型TDO之间保守的残基形成。生物化学和细胞研究表明，色氨酸结合在这个外切位点不影响酶催化，而是它阻碍了降解的hTDO通过泛素依赖性蛋白酶体途径。因此，该exo位点可能为hTDO的细胞降解提供新的L-Trp介导的调节机制，这可能在人类疾病中具有重要意义。
Tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) play a central role in tryptophan metabolism and are involved in many cellular and disease processes. Here we report the crystal structure of human TDO (hTDO) in a ternary complex with the substrates L-Trp and O2 and in a binary complex with the product N-formylkynurenine (NFK), defining for the first time the binding modes of both substrates and the product of this enzyme. The structure indicates that the dioxygenation reaction is initiated by a direct attack of O2 on the C2 atom of the L-Trp indole ring. The structure also reveals an exo binding site for L-Trp, located ~42 Å from the active site and formed by residues conserved among tryptophan-auxotrophic TDOs. Biochemical and cellular studies indicate that Trp binding at this exo site does not affect enzyme catalysis but instead it retards the degradation of hTDO through the ubiquitin-dependent proteasomal pathway. This exo site may therefore provide a novel L-Trp-mediated regulation mechanism for cellular degradation of hTDO, which may have important implications in human diseases.
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