Molecular basis for catalysis and substrate-mediated cellular stabilization of human tryptophan 2,3-dioxygenase
نویسندگان
چکیده
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.
منابع مشابه
Molecular insights into substrate recognition and catalysis by tryptophan 2,3-dioxygenase.
Tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) constitute an important, yet relatively poorly understood, family of heme-containing enzymes. Here, we report extensive structural and biochemical studies of the Xanthomonas campestris TDO and a related protein SO4414 from Shewanella oneidensis, including the structure at 1.6-A resolution of the catalytically active, ferrous...
متن کاملMolecular basis for the substrate stereoselectivity in tryptophan dioxygenase.
Tryptophan dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) are the only two heme proteins that catalyze the oxidation reaction of tryptophan (Trp) to N-formylkynurenine. While human IDO is able to oxidize both L- and D-Trp, human TDO (hTDO) displays major specificity for L-Trp. In this work, we aim to interrogate the molecular basis for the substrate stereoselectivity of hTDO. Our previ...
متن کاملHeme-dependent Tryptophan Oxidation: Mechanistic Studies on Tryptophan 2,3-Dioxygenase and MauG
Hemoenzymes are prevalent in nature and participate in a wide range of biological activities. Frequently, high-valence iron intermediates are involved in the catalytic events of these enzymes, especially when the activation of peroxide or dioxygen is involved. Building on the fundamental framework of iron-oxygen chemistry, the mechanistic understandings of these enzymes and their reactive inter...
متن کاملOxidation of L-tryptophan in biology: a comparison between tryptophan 2,3-dioxygenase and indoleamine 2,3-dioxygenase.
The family of haem dioxygenases catalyse the initial oxidative cleavage of L-tryptophan to N-formylkynurenine, which is the first, rate-limiting, step in the L-kynurenine pathway. In the present paper, we discuss and compare structure and function across the family of haem dioxygenases by focusing on TDO (tryptophan 2,3-dioxygenase) and IDO (indoleamine 2,3-dioxygenase), including a review of r...
متن کاملThe oxygenated complexes of the two catalytically active oxidation-reduction states of L-tryptophan-2,3-dioxygenase.
The oxygenated complexes of the two catalytically active forms of pseudomonad and rat liver L-tryptophan-2,3-dioxygenase (EC 1.13.11.11) have been studied. As was previously reported (ISHIMURA, Y., NORZAKI, M., HAYAISHI, O., TAMURA, M., AND YAMAZAK-I I. (1970) J. Biol. Chem. 245, 3593-3602), we observe that the fully reduced form of pseudomonad tryptophan oxygenase during steady state catalysis...
متن کامل