title: Crystal structures of the catalytic domain of a novel glycohydrolase family 23 chitinase from Ralstonia sp. A-471 reveals a unique arrangement of the catalytic residues for inverting chitin hydrolysis.
abstract: Chitinase C from Ralstonia sp. A-471 (Ra-ChiC) has a catalytic domain sequence similar to goose-type (G-type) lysozymes and, unlike other chitinases, belongs to glycohydrolase (GH) family 23. Using NMR spectroscopy, however, Ra-ChiC was found to interact only with the chitin dimer but not with the peptidoglycan fragment. Here we report the crystal structures of wild-type, E141Q, and E162Q of the catalytic domain of Ra-ChiC with or without chitin oligosaccharides. Ra-ChiC has a substrate-binding site including a tunnel-shaped cavity, which determines the substrate specificity. Mutation analyses based on this structural information indicated that a highly conserved Glu-141 acts as a catalytic acid, and that Asp-226 located at the roof of the tunnel activates a water molecule as a catalytic base. The unique arrangement of the catalytic residues makes a clear contrast to the other GH23 members and also to inverting GH19 chitinases.
authors: Quantum Beam Science Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan.
authors: Takao
authors: T
authors: Arimori
authors: Noriko
authors: N
authors: Kawamoto
authors: Shoko
authors: S
authors: Shinya
authors: Nobuo
authors: N
authors: Okazaki
authors: Masami
authors: M
authors: Nakazawa
authors: Kazutaka
authors: K
authors: Miyatake
authors: Tamo
authors: T
authors: Fukamizo
authors: Mitsuhiro
authors: M
authors: Ueda
authors: Taro
authors: T
authors: Tamada
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry*; D020134:Catalytic Domain; D002686:Chitin / Q000737:chemistry*; D002688:Chitinases / Q000737:chemistry*; D018360:Crystallography, X-Ray; D048389:Gadus morhua; D006026:Glycoside Hydrolases / Q000737:chemistry*; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010940:Plant Proteins; D043367:Ralstonia / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D010940:Plant Proteins; D002686:Chitin; D006026:Glycoside Hydrolases; D002688:Chitinases; C119825:chitinase C
keywords: Chitinase; Crystal Structure; Glycoside Hydrolases; Mutagenesis Site Specific; Oligosaccharide
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