Molecular basis for the substrate stereoselectivity in tryptophan dioxygenase.

LUCIANA CAPECE; ARIEL LEWIS BALLESTER; MARCELO A. MARTI; DARIO A ESTRIN; SYUN-RU YEH

BIOCHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2011 p. 10910 - 10918

0006-2960

Tryptophan dioxygenase (TDO) and indole-amine 2,3-dioxygenase (IDO) are the only two heme proteinsthat 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 forL-Trp. In this work, we aim to interrogate the molecular basisfor the substrate stereoselectivity of hTDO. Our previousmolecular dynamics simulation studies of Xanthomonascampestris TDO (xcTDO) showed that a hydrogen bond between T254 (T342 in hTDO) and the ammonium group of thesubstrate is present in the L-Trp-bound enzyme, but not in the D-Trp-bound enzyme. The fact that this is the only notablestructural alteration induced by the change in the stereo structure of the substrate prompted us to produce and characterize theT342A mutant of hTDO to evaluate the structural role of T342 in controlling the substrate stereoselectivity of the enzyme. Theexperimental results indicate that the mutation only slightly perturbs the global structural properties of the enzyme but totallyabolishes the substrate stereoselectivity. Molecular dynamics simulations of xcTDO show that T254 controls the substratestereoselectivity of the enzyme by (i) modulating the hydrogen bonding interaction between the NH 3+ group and epoxideoxygen of the ferryl−indole 2,3-epoxide intermediate of the e