title: The crystal structure of enamidase: a bifunctional enzyme of the nicotinate catabolism.
abstract: The hydrolysis of 1,4,5,6-tetrahydro-6-oxonicotinate to 2-formylglutarate is a central step in the catabolism of nicotinate in several Clostridia and Proteobacteria. This reaction is catalyzed by the novel enzyme enamidase, a new member of the amidohydrolase superfamily as indicated by its unique reaction, sequence relationship, and the stoichiometric binding of iron and zinc. A hallmark of enamidase is its capability to catalyze a two-step reaction: the initial decyclization of 1,4,5,6-tetrahydro-6-oxonicotinate leading to 2-(enamine)glutarate followed by an additional hydrolysis step yielding (S)-2-formylglutarate. Here, we present the crystal structure of enamidase from Eubacterium barkeri at 1.9 A resolution, providing a structural basis for catalysis and suggesting a mechanism for its exceptional activity and enantioselectivity. The enzyme forms a 222-symmetric tetramer built up by a dimer of dimers. Each enamidase monomer consists of a composite beta-sandwich domain and an (alpha/beta)(8)-TIM-barrel domain harboring the active site. With its catalytic binuclear metal center comprising both zinc and iron ions, enamidase represents a special case of subtype II amidohydrolases.
authors.affiliation: Philipps-Universität Marburg, Fachbereich Chemie, Marburg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kress
authors.forename: Ashraf
authors.initials: A
authors.lastname: Alhapel
authors.forename: Antonio J
authors.initials: AJ
authors.lastname: Pierik
authors.forename: Lars-Oliver
authors.initials: LO
authors.lastname: Essen
mesh_terms: D000595:Amino Acid Sequence; D000619:Aminohydrolases / Q000737:chemistry* / Q000302:isolation & purification; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D019281:Dimerization; D005051:Eubacterium / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009525:Niacin / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D009525:Niacin; D000619:Aminohydrolases