The role of residue 238 of TEM-1 beta-lactamase in the hydrolysis of extended-spectrum antibiotics.
beta-Lactamases inactivate beta-lactam antibiotics by catalyzing the hydrolysis of the amide bond in the beta-lactam ring. The plasmid-encoded class A TEM-1 beta-lactamase is a commonly encountered beta-lactamase. It is able to inactivate penicillins and cephalosporins but not extended-spectrum antibiotics. However, TEM-1-derived natural variants containing the G238S amino acid substitution display increased hydrolysis of extended-spectrum antibiotics. Two models have been proposed to explain the role of the G238S substitution in hydrolysis of extended-spectrum antibiotics. The first proposes a direct hydrogen bond of the Ser238 side chain to the oxime group of extended-spectrum antibiotics. The second proposes that steric conflict with surrounding residues, due to increased side chain volume, leads to a more accessible active site pocket. To assess the validity of each model, TEM-1 mutants with amino acids substitutions of Ala, Ser, Cys, Thr, Asn, and Val have been constructed. Kinetic analysis of these enzymes with penicillins and cephalosporins suggests that a hydrogen bond is necessary but not sufficient to achieve the hydrolytic activity of the G238S enzyme for the extended-spectrum antibiotics cefotaxime and ceftazidime. In addition, it appears that the new hydrogen bond interaction is to a site on the enzyme rather than directly to the extended-spectrum antibiotic. The data indicate that, for the G238S substitution, a combination of an optimal side chain volume and hydrogen bonding potential results in the most versatile and advantageous antibiotic hydrolytic spectrum for bacterial resistance to extended-spectrum antibiotics.
Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA.
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D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D002384:Catalysis; D006860:Hydrogen Bonding; D006868:Hydrolysis; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D016297:Mutagenesis, Site-Directed; D001618:beta-Lactamases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D047090:beta-Lactams
D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D001618:beta-Lactamases; C034413:beta-lactamase TEM-1