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Structural basis for cofactor-independent dioxygenation of N-heteroaromatic compounds at the alpha/beta-hydrolase fold

Journal Article


Abstract


  • Enzymatic catalysis of oxygenation reactions in the absence of metal or organic cofactors is a considerable biochemical challenge. The CO-forming 1-H-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase (HOD) from Arthrobacter nitroguajacolicus Rü61a and 1-H-3-hydroxy-4-oxoquinoline 2,4-dioxygenase (QDO) from Pseudomonas putida 33/1 are homologous cofactor-independent dioxygenases involved in the breakdown of N-heteroaromatic compounds. To date, they are the only dioxygenases suggested to belong to the α/β-hydrolase fold superfamily. Members of this family typically catalyze hydrolytic processes rather than oxygenation reactions. We present here the crystal structures of both HOD and QDO in their native state as well as the structure of HOD in complex with its natural 1-H-3-hydroxy-4-oxoquinaldine substrate, its N-acetylanthranilate reaction product, and chloride as dioxygen mimic. HOD and QDO are structurally very similar. They possess a classical α/β-hydrolase fold core domain additionally equipped with a cap domain. Organic substrates bind in a preorganized active site with an orientation ideally suited for selective deprotonation of their hydroxyl group by a His/Asp charge-relay system affording the generation of electron-donating species. The “oxyanion hole” of the α/β-hydrolase fold, typically employed to stabilize the tetrahedral intermediate in ester hydrolysis reactions, is utilized here to host and control oxygen chemistry, which is proposed to involve a peroxide anion intermediate. Product release by proton back transfer from the catalytic histidine is driven by minimization of intramolecular charge repulsion. Structural and kinetic data suggest a nonnucleophilic general-base mechanism. Our analysis provides a framework to explain cofactor-independent dioxygenation within a protein architecture generally employed to catalyze hydrolytic reactions.

Authors


  •   Steiner, Roberto A. (external author)
  •   Janssen, Helge J. (external author)
  •   Roversi, Pietro (external author)
  •   Oakley, Aaron J.
  •   Fetzner, Susanne (external author)

Publication Date


  • 2010

Citation


  • Steiner, R. A., Janssen, H. J., Roversi, P., Oakley, A. J. & Fetzner, S. (2010). Structural basis for cofactor-independent dioxygenation of N-heteroaromatic compounds at the alpha/beta-hydrolase fold. Proceedings of the National Academy of Sciences of USA, 107 (2), 657-662.

Scopus Eid


  • 2-s2.0-76249120623

Ro Metadata Url


  • http://ro.uow.edu.au/scipapers/5180

Number Of Pages


  • 5

Start Page


  • 657

End Page


  • 662

Volume


  • 107

Issue


  • 2

Place Of Publication


  • http://www.pnas.org/

Abstract


  • Enzymatic catalysis of oxygenation reactions in the absence of metal or organic cofactors is a considerable biochemical challenge. The CO-forming 1-H-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase (HOD) from Arthrobacter nitroguajacolicus Rü61a and 1-H-3-hydroxy-4-oxoquinoline 2,4-dioxygenase (QDO) from Pseudomonas putida 33/1 are homologous cofactor-independent dioxygenases involved in the breakdown of N-heteroaromatic compounds. To date, they are the only dioxygenases suggested to belong to the α/β-hydrolase fold superfamily. Members of this family typically catalyze hydrolytic processes rather than oxygenation reactions. We present here the crystal structures of both HOD and QDO in their native state as well as the structure of HOD in complex with its natural 1-H-3-hydroxy-4-oxoquinaldine substrate, its N-acetylanthranilate reaction product, and chloride as dioxygen mimic. HOD and QDO are structurally very similar. They possess a classical α/β-hydrolase fold core domain additionally equipped with a cap domain. Organic substrates bind in a preorganized active site with an orientation ideally suited for selective deprotonation of their hydroxyl group by a His/Asp charge-relay system affording the generation of electron-donating species. The “oxyanion hole” of the α/β-hydrolase fold, typically employed to stabilize the tetrahedral intermediate in ester hydrolysis reactions, is utilized here to host and control oxygen chemistry, which is proposed to involve a peroxide anion intermediate. Product release by proton back transfer from the catalytic histidine is driven by minimization of intramolecular charge repulsion. Structural and kinetic data suggest a nonnucleophilic general-base mechanism. Our analysis provides a framework to explain cofactor-independent dioxygenation within a protein architecture generally employed to catalyze hydrolytic reactions.

Authors


  •   Steiner, Roberto A. (external author)
  •   Janssen, Helge J. (external author)
  •   Roversi, Pietro (external author)
  •   Oakley, Aaron J.
  •   Fetzner, Susanne (external author)

Publication Date


  • 2010

Citation


  • Steiner, R. A., Janssen, H. J., Roversi, P., Oakley, A. J. & Fetzner, S. (2010). Structural basis for cofactor-independent dioxygenation of N-heteroaromatic compounds at the alpha/beta-hydrolase fold. Proceedings of the National Academy of Sciences of USA, 107 (2), 657-662.

Scopus Eid


  • 2-s2.0-76249120623

Ro Metadata Url


  • http://ro.uow.edu.au/scipapers/5180

Number Of Pages


  • 5

Start Page


  • 657

End Page


  • 662

Volume


  • 107

Issue


  • 2

Place Of Publication


  • http://www.pnas.org/