CONICET | Buscador de Institutos y Recursos Humanos

Tryptophan dioxygenase (TDO) and Indoleamine 2,3 dioxygenase (IDO) are two heme containing enzymes, which catalyze the conversion of L-Trp to N-formylkynurenine (NFK). hIDO has recently caught the attention of the scientific community due to its implications in the immune system, where it has been found to be critical for T-cell mediated immunity, and possible target for treating cancer. Despite decades of effort the reaction mechanism remains elusive, being an active filed current research. In this work we use a combination of simulation techniques to study the process for ligand migration, stereoselectivity and reaction mechanism in TDO and IDO. The results indicate that while TDO dysplays a rigid active site that keeps Trp in a unique position, IDOs active site is much more flexible, and allows different conformations for the substrate. Additionaly, the reaction mechanism analysis indicated that, in contrast with previous proposals, the reaction isinitiated by a direct attack of heme-bound dioxygen to the C2=C3bond of the indole ring, leading to a protein-stabilized 2,3-alkylperoxide transition state and a ferryl-epoxide intermediate. The novel sequential two-step oxygen addition mechanism is fully supported by recent resonance Raman data that allowed identification of the ferryl intermediate. Further computational evidence indicates that the reaction finishes with a proton assisted epoxide opening, combined with the ferryl attack to the epoxide C2, leading to the product NFK. Taken together our data allows determination of key molecular information, useful for the future design of more potent selective IDO inhibitors. &lt;!-- @page { size: 21cm 29.7cm; margin: 2cm } P { margin-bottom: 0.21cm } --&gt;