Publications

• Molecular and functional analysis of nicotinate catabolism in Eubacterium barkeri.

  Alhapel A., Darley D.J., Wagener N., Eckel E., Elsner N., Pierik A.J.

  The anaerobic soil bacterium Eubacterium barkeri catabolizes nicotinate to pyruvate and propionate via a unique fermentation. A full molecular characterization of nicotinate fermentation in this organism was accomplished by the following results: (i) A 23.2-kb DNA segment with a gene cluster encod ... >> More

  The anaerobic soil bacterium Eubacterium barkeri catabolizes nicotinate to pyruvate and propionate via a unique fermentation. A full molecular characterization of nicotinate fermentation in this organism was accomplished by the following results: (i) A 23.2-kb DNA segment with a gene cluster encoding all nine enzymes was cloned and sequenced, (ii) two chiral intermediates were discovered, and (iii) three enzymes were found, completing the hitherto unknown part of the pathway. Nicotinate dehydrogenase, a (nonselenocysteine) selenium-containing four-subunit enzyme, is encoded by ndhF (FAD subunit), ndhS (2 x [2Fe-2S] subunit), and by the ndhL/ndhM genes. In contrast to all enzymes of the xanthine dehydrogenase family, the latter two encode a two-subunit molybdopterin protein. The 6-hydroxynicotinate reductase, catalyzing reduction of 6-hydroxynicotinate to 1,4,5,6-tetrahydro-6-oxonicotinate, was purified and shown to contain a covalently bound flavin cofactor, one [2Fe-2S](2+/1+) and two [4Fe-4S](2+/1+) clusters. Enamidase, a bifunctional Fe-Zn enzyme belonging to the amidohydrolase family, mediates hydrolysis of 1,4,5,6-tetrahydro-6-oxonicotinate to ammonia and (S)-2-formylglutarate. NADH-dependent reduction of the latter to (S)-2-(hydroxymethyl)glutarate is catalyzed by a member of the 3-hydroxyisobutyrate/phosphogluconate dehydrogenase family. A [4Fe-4S]-containing serine dehydratase-like enzyme is predicted to form 2-methyleneglutarate. After the action of the coenzyme B(12)-dependent 2-methyleneglutarate mutase and 3-methylitaconate isomerase, an aconitase and isocitrate lyase family pair of enzymes, (2R,3S)-dimethylmalate dehydratase and lyase, completes the pathway. Genes corresponding to the first three enzymes of the E. barkeri nicotinate catabolism were identified in nine Proteobacteria. << Less

  Proc. Natl. Acad. Sci. U.S.A. 103:12341-12346(2006) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• Structural and kinetic properties of a beta-hydroxyacid dehydrogenase involved in nicotinate fermentation.

  Reitz S., Alhapel A., Essen L.O., Pierik A.J.

  2-(Hydroxymethyl)glutarate dehydrogenase, the fourth enzyme of the anaerobic nicotinate fermentation pathway of Eubacterium barkeri, catalyzes the NADH-dependent conversion between (S)-2-formylglutarate and (S)-2-(hydroxymethyl)glutarate. As shown by its 2.3-A crystal structure, this enzyme is a n ... >> More

  2-(Hydroxymethyl)glutarate dehydrogenase, the fourth enzyme of the anaerobic nicotinate fermentation pathway of Eubacterium barkeri, catalyzes the NADH-dependent conversion between (S)-2-formylglutarate and (S)-2-(hydroxymethyl)glutarate. As shown by its 2.3-A crystal structure, this enzyme is a novel member of the beta-hydroxyacid dehydrogenase family and adopts a tetrameric architecture with monomers interacting via their C-terminal catalytic domains. The NAD-binding domains protrude heterogeneously from the central, tetrameric core with domain rotation angles differing up to 12 degrees. Kinetic properties of the enzyme, including NADH inhibition constants, were determined. A strong NADH binding in contrast to weaker NAD(+) binding of the protein was inferred from fluorometrically determined binding constants for the dinucleotide cofactor. The data support either an Iso Ordered Bi Bi mechanism or a more common Ordered Bi Bi mechanism as found in other dehydrogenases. << Less

  J. Mol. Biol. 382:802-811(2008) [PubMed] [EuropePMC]