TY - JOUR
T1 - The first step of the dioxygenation reaction carried out by tryptophan dioxygenase and indoleamine 2,3-dioxygenase as revealed by quantum mechanical/molecular mechanical studies
AU - Capece, Luciana
AU - Lewis-Ballester, Ariel
AU - Batabyal, Dipanwita
AU - Di Russo, Natali
AU - Yeh, Syun Ru
AU - Estrin, Dario A.
AU - Marti, Marcelo A.
N1 - Funding Information:
Acknowledgments This work was partially supported by grants from Universidad de Buenos Aires 08-X625 to M.A.M. and 08-X074 to D.A.E., ANPCYT 07-1650 to M.A.M. and 06-25667 to D.A.E., Conicet PIP 01207 and a Guggenheim Foundation grant awarded to D.A.E, and NIH Molecular Biophysics Training Grant GM008572 to A.L.-B. D.A.E., and M.A.M. are members of CONICET, L.C. holds a CONICET Ph.D. fellowship. Computer power was provided by the Centro de Computacion de Alto Rendimiento (CECAR) at Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. We thank Pau Arroyo Mañez for useful discussions.
PY - 2010/8
Y1 - 2010/8
N2 - Tryptophan dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) are two heme-containing enzymes which catalyze the conversion of L-tryptophan to N-formylkynurenine (NFK). In mammals, TDO is mostly expressed in liver and is involved in controlling homeostatic serum tryptophan concentrations, whereas IDO is ubiquitous and is involved in modulating immune responses. Previous studies suggested that the first step of the dioxygenase reaction involves the deprotonation of the indoleamine group of the substrate by an evolutionarily conserved distal histidine residue in TDO and the hemebound dioxygen in IDO. Here, we used classical molecular dynamics and hybrid quantum mechanical/molecular mechanical methods to evaluate the base-catalyzed mechanism. Our data suggest that the deprotonation of the indoleamine group of the substrate by either histidine in TDO or heme-bound dioxygen in IDO is not energetically favorable. Instead, the dioxygenase reaction can be initiated by a direct attack of heme-bound dioxygen on the C 2=C 3 bond of the indole ring, leading to a protein-stabilized 2,3-alkylperoxide transition state and a ferryl epoxide intermediate, which subsequently recombine to generate NFK. The novel sequential two-step oxygen addition mechanism is fully supported by our recent resonance Raman data that allowed identification of the ferryl intermediate (Lewis-Ballester et al. in Proc Natl Acad Sci USA 106:17371-17376, 2009). The results reveal the subtle differences between the TDO and IDO reactions and highlight the importance of protein matrix in modulating stereoelectronic factors for oxygen activation and the stabilization of both transition and intermediate states.
AB - Tryptophan dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) are two heme-containing enzymes which catalyze the conversion of L-tryptophan to N-formylkynurenine (NFK). In mammals, TDO is mostly expressed in liver and is involved in controlling homeostatic serum tryptophan concentrations, whereas IDO is ubiquitous and is involved in modulating immune responses. Previous studies suggested that the first step of the dioxygenase reaction involves the deprotonation of the indoleamine group of the substrate by an evolutionarily conserved distal histidine residue in TDO and the hemebound dioxygen in IDO. Here, we used classical molecular dynamics and hybrid quantum mechanical/molecular mechanical methods to evaluate the base-catalyzed mechanism. Our data suggest that the deprotonation of the indoleamine group of the substrate by either histidine in TDO or heme-bound dioxygen in IDO is not energetically favorable. Instead, the dioxygenase reaction can be initiated by a direct attack of heme-bound dioxygen on the C 2=C 3 bond of the indole ring, leading to a protein-stabilized 2,3-alkylperoxide transition state and a ferryl epoxide intermediate, which subsequently recombine to generate NFK. The novel sequential two-step oxygen addition mechanism is fully supported by our recent resonance Raman data that allowed identification of the ferryl intermediate (Lewis-Ballester et al. in Proc Natl Acad Sci USA 106:17371-17376, 2009). The results reveal the subtle differences between the TDO and IDO reactions and highlight the importance of protein matrix in modulating stereoelectronic factors for oxygen activation and the stabilization of both transition and intermediate states.
KW - 3-dioxygenase
KW - Indoleamine 2
KW - Molecular dynamics
KW - Quantum mechanics/molecular mechanics
KW - Tryptophan dioxygenase
KW - Tryptophan dioxygenation
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U2 - 10.1007/s00775-010-0646-x
DO - 10.1007/s00775-010-0646-x
M3 - Article
C2 - 20361220
AN - SCOPUS:77957933059
SN - 0949-8257
VL - 15
SP - 811
EP - 823
JO - Journal of Biological Inorganic Chemistry
JF - Journal of Biological Inorganic Chemistry
IS - 6
ER -