The 3-D structure of a zinc metallo-beta-lactamase from Bacillus cereus reveals a new type of protein fold.
The 3-D structure of Bacillus cereus (569/H/9) beta-lactamase (EC 3.5.2.6), which catalyses the hydrolysis of nearly all beta-lactams, has been solved at 2.5 A resolution by the multiple isomorphous replacement method, with density modification and phase combination, from crystals of the native protein and of a specially designed mutant (T97C). The current model includes 212 of the 227 amino acid residues, the zinc ion and 10 water molecules. The protein is folded into a beta beta sandwich with helices on each external face. To our knowledge, this fold has never been observed. An approximate internal molecular symmetry is found, with a 2-fold axis passing roughly through the zinc ion and suggesting a possible gene duplication. The active site is located at one edge of the beta beta sandwich and near the N-terminal end of a helix. The zinc ion is coordinated by three histidine residues (86, 88 and 149) and a water molecule. A sequence comparison of the relevant metallo-beta-lactamases, based on this protein structure, highlights a few well-conserved amino acid residues. The structure shows that most of these residues are in the active site. Among these, aspartic acid 90 and histidine 210 participate in a proposed catalytic mechanism for beta-lactam hydrolysis.
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Institut de Biologie Structurale Jean-Pierre Ebel (CEA-CNRS), Laboratoire de Cristallographie Macromoléculaire, Grenoble, France.
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Duée
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Galleni
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Duez
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Frère
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Dideberg
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D000595:Amino Acid Sequence; D001409:Bacillus cereus / Q000201:enzymology*; D001483:Base Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D008667:Metalloproteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D015203:Reproducibility of Results; D017386:Sequence Homology, Amino Acid; D015032:Zinc / Q000737:chemistry*; D001618:beta-Lactamases / Q000737:chemistry* / Q000378:metabolism
D008667:Metalloproteins; D001618:beta-Lactamases; D015032:Zinc