title: Crystal structure of N-carbamyl-D-amino acid amidohydrolase with a novel catalytic framework common to amidohydrolases.
abstract: BACKGROUND
  N-carbamyl-D-amino acid amidohydrolase (DCase) catalyzes the hydrolysis of N-carbamyl-D-amino acids to the corresponding D-amino acids, which are useful intermediates in the preparation of beta-lactam antibiotics. To understand the catalytic mechanism of N-carbamyl-D-amino acid hydrolysis, the substrate specificity and thermostability of the enzyme, we have determined the structure of DCase from Agrobacterium sp. strain KNK712.
  
  
  RESULTS
  The crystal structure of DCase has been determined to 1.7 A resolution. The enzyme forms a homotetramer and each monomer consists of a variant of the alpha + beta fold. The topology of the enzyme comprises a sandwich of parallel beta sheets surrounded by two layers of alpha helices, this topology has not been observed in other amidohydrolases such as the N-terminal nucleophile (Ntn) hydrolases.
  
  
  CONCLUSIONS
  The catalytic center could be identified and consists of Glu46, Lys126 and Cys171. Cys171 was found to be the catalytic nucleophile, and its nucleophilic character appeared to be increased through general-base activation by Glu46. DCase shows only weak sequence similarity with a family of amidohydrolases, including beta-alanine synthase, aliphatic amidases and nitrilases, but might share highly conserved residues in a novel framework, which could provide a possible explanation for the catalytic mechanism for this family of enzymes.
authors.affiliation: Kaneka Corporation, Takasago-cho, Takasago, 676-8688, Japan. tnakai@kaneka.co.jp
authors.forename: T
authors.initials: T
authors.lastname: Nakai
authors.forename: T
authors.initials: T
authors.lastname: Hasegawa
authors.forename: E
authors.initials: E
authors.lastname: Yamashita
authors.forename: M
authors.initials: M
authors.lastname: Yamamoto
authors.forename: T
authors.initials: T
authors.lastname: Kumasaka
authors.forename: T
authors.initials: T
authors.lastname: Ueki
authors.forename: H
authors.initials: H
authors.lastname: Nanba
authors.forename: Y
authors.initials: Y
authors.lastname: Ikenaka
authors.forename: S
authors.initials: S
authors.lastname: Takahashi
authors.forename: M
authors.initials: M
authors.lastname: Sato
authors.forename: T
authors.initials: T
authors.lastname: Tsukihara
mesh_terms: D000581:Amidohydrolases / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D012231:Rhizobium / Q000201:enzymology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014867:Water / Q000737:chemistry
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; D014867:Water; D000581:Amidohydrolases; C020047:dihydropyrimidinase