Refined crystal structure of β-lactamase from Citrobacter freundii indicates a mechanism for β-lactam hydrolysis

• Published in: Nature (London) Vol. 343; no. 6255; pp. 284 - 288
• Main Authors: Oefner, C, D'Arcy, A, Daly, J. J, Gubernator, K, Charnas, R. L, Heinze, I, Hubschwerlen, C, Winkler, F. K
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 18-01-1990; Nature Publishing Group
• Subjects: Amides; Amino Acid Sequence; Amino acids; Anti-Bacterial Agents - biosynthesis; Antibiotic resistance; Antibiotics; Aztreonam; beta -lactamase; beta-Lactamases - metabolism; beta-Lactams; Binding Sites; Biochemistry; Catalysis; Cephalosporins; Citrobacter; Citrobacter - enzymology; Citrobacter freundii; Crystal structure; Enzymes; Exact sciences and technology; Hydrogen bonds; Hydrolysis; Hypotheses; Lethal effects; Mathematical analysis; Mathematics; Models, Molecular; Molecular modelling; Molecular Sequence Data; Potential theory; Protein Conformation; Proteins; Sciences and techniques of general use; Serine; Substrates; β-Lactam antibiotics; Antibiotic; Enzyme; Active site; Molecular model; Bacteria; β-Lactamase; Mechanism of action; Citrobacter freundii; Spatial structure; Enterobacteriaceae; Crystalline structure
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/343284a0

Beta-Lactamases (EC 3.5.2.6, 'penicillinases') are a family of enzymes that protect bacteria against the lethal effects of cell-wall synthesis of penicillins, cephalosporins and related antibiotic agents, by hydrolysing the beta-lactam antibiotics to biologically inactive compounds. Their production can, therefore, greatly contribute to the clinical problem of antibiotic resistance. Three classes of beta-lactamases--A, B and C--have been identified on the basis of their amino-acid sequence; class B beta-lactamases are metalloenzymes, and are clearly distinct from members of class A and C beta-lactamases, which both contain an active-site serine residue involved in the formation of an acyl enzyme with beta-lactam substrates during catalysis. It has been predicted that class C beta-lactamases share common structural features with D,D-carboxypeptidases and class A beta-lactamases, and further, suggested that class A and class C beta-lactamases have the same evolutionary origin as other beta-lactam target enzymes. We report here the refined three-dimensional structure of the class C beta-lactamase from Citrobacter freundii at 2.0-A resolution and confirm the predicted structural similarity. The refined structure of the acyl-enzyme formed with the monobactam inhibitor aztreonam at 2.5-A resolution defines the enzyme's active site and, along with molecular modelling, indicates a mechanism for beta-lactam hydrolysis. This leads to the hypothesis that Tyr 150 functions as a general base during catalysis.