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Published on: October 3, 2018
Molecular basis for the substrate stereoselectivity in tryptophan dioxygenase
Luciana Capece1, Ariel Lewis-Ballester, Marcelo A Marti
1Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE-CONICET Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires C1428EHA, Argentina.
Human tryptophan dioxygenase (hTDO) selectively binds L-tryptophan. A key mutation (T342A) abolishes this stereoselectivity, revealing Threonine 342
Area of Science:
- Biochemistry
- Enzymology
- Structural Biology
Background:
- Tryptophan dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO) are heme enzymes catalyzing tryptophan oxidation.
- Human TDO (hTDO) exhibits stereoselectivity for L-tryptophan, unlike human IDO.
- Understanding hTDO substrate stereoselectivity is crucial for its biological roles.
Purpose of the Study:
- To investigate the molecular basis of substrate stereoselectivity in human TDO (hTDO).
- To evaluate the role of Threonine 342 (T342) in hTDO's stereoselective binding of tryptophan.
Main Methods:
- Site-directed mutagenesis to create the hTDO T342A mutant.
- Biochemical characterization of the wild-type and mutant hTDO enzymes.
- Molecular dynamics simulations of Xanthomonas campestris TDO (xcTDO) and its substrate interactions.
Main Results:
- The T342A mutation in hTDO did not significantly alter global enzyme structure.
- The T342A mutation completely abolished the stereoselectivity of hTDO for L-tryptophan.
- Molecular dynamics simulations indicated T254 (homologous to hTDO's T342) controls stereoselectivity via hydrogen bonding and loop dynamics.
Conclusions:
- Threonine 342 is critical for the substrate stereoselectivity of human TDO.
- T342 influences substrate binding by modulating key hydrogen bonds and active site loop dynamics.
- These findings elucidate the structural determinants of hTDO's specificity in tryptophan metabolism.
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