title: Crystal structure of Helicobacter pylori formamidase AmiF reveals a cysteine-glutamate-lysine catalytic triad.
abstract: Helicobacter pylori AmiF formamidase that hydrolyzes formamide to produce formic acid and ammonia belongs to a member of the nitrilase superfamily. The crystal structure of AmiF was solved to 1.75A resolution using single-wavelength anomalous dispersion methods. The structure consists of a homohexamer related by 3-fold symmetry in which each subunit has an alpha-beta-beta-alpha four-layer architecture characteristic of the nitrilase superfamily. One exterior alpha layer faces the solvent, whereas the other one associates with that of the neighbor subunit, forming a tight alpha-beta-beta-alpha-alpha-beta-beta-alpha dimer. The apo and liganded crystal structures of an inactive mutant C166S were also determined to 2.50 and 2.30 A, respectively. These structures reveal a small formamide-binding pocket that includes Cys(166), Glu(60), and Lys(133) catalytic residues, in which Cys(166) acts as a nucleophile. Analysis of the liganded AmiF and N-carbamoyl d-amino acid amidohydrolase binding pockets reveals a common Cys-Glu-Lys triad, another conserved glutamate, and different subsets of ligand-binding residues. Molecular dynamic simulations show that the conserved triad has minimal fluctuations, catalyzing the hydrolysis of a specific nitrile or amide in the nitrilase superfamily efficiently.
authors.affiliation: Institute of Molecular and Cellular Biology and Department of Life Science, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: Chiu-Lien
authors.initials: CL
authors.lastname: Hung
authors.forename: Jia-Hsin
authors.initials: JH
authors.lastname: Liu
authors.forename: Wei-Chun
authors.initials: WC
authors.lastname: Chiu
authors.forename: Shao-Wei
authors.initials: SW
authors.lastname: Huang
authors.forename: Jenn-Kang
authors.initials: JK
authors.lastname: Hwang
authors.forename: Wen-Ching
authors.initials: WC
authors.lastname: Wang
mesh_terms: D000581:Amidohydrolases / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry*; D018698:Glutamic Acid / Q000737:chemistry*; D016480:Helicobacter pylori / Q000201:enzymology*; D008024:Ligands; D008239:Lysine / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D008024:Ligands; D018698:Glutamic Acid; D000581:Amidohydrolases; C101846:formamidase; D008239:Lysine; D003545:Cysteine