Molecular and active-site structure of a Bacillus 1,3-1,4-beta-glucanase.
The three-dimensional structure of the hybrid Bacillus 1,3-1,4-beta-glucanase (beta-glucanase; 1,3-1,4-beta-D-glucan 4-glucanohydrolase, lichenase, EC 3.2.1.73) designated H(A16-M) was determined by x-ray crystallography at a resolution of 2.0 A and refined to an R value of 16.4% using stereochemical restraints. The protein molecule consists mainly of two seven-stranded antiparallel beta-pleated sheets arranged atop each other to form a compact, sandwich-like structure. A channel crossing one side of the protein molecule accommodates an inhibitor, 3,4-epoxybutyl beta-D-cellobioside, which binds covalently to the side chain of Glu-105, as seen in a crystal structure analysis at 2.8-A resolution of the protein-inhibitor complex (R = 16.8%). That Glu-105 may be indispensible for enzyme catalysis by H(A16-M) is suggested by site-directed mutagenesis of this residue, which inevitably leads to an inactive enzyme.
Keitel
T
T
Institut für Kristallographie, Freie Universität, Berlin, Federal Republic of Germany.
Simon
O
O
Borriss
R
R
Heinemann
U
U
D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology*; D001665:Binding Sites; D002240:Carbohydrate Sequence; D004852:Epoxy Compounds / Q000378:metabolism / Q000494:pharmacology; D005936:Glucans / Q000378:metabolism; D005960:Glucosides / Q000378:metabolism / Q000494:pharmacology; D005971:Glutamates; D018698:Glutamic Acid; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity; D014961:X-Ray Diffraction
D004852:Epoxy Compounds; D005936:Glucans; D005960:Glucosides; D005971:Glutamates; D011994:Recombinant Proteins; C081533:3,4-epoxybutyl-beta-cellobioside; D018698:Glutamic Acid; D006026:Glycoside Hydrolases; C028020:licheninase