title: Unexpected enzyme TEM-126: role of mutation Asp179Glu.
abstract: The clinical isolate Escherichia coli CF884 exhibited low-level resistance to ceftazidime (4 mug/ml) by a positive double-disk synergy test and apparent susceptibility to cefuroxime, cefotaxime, cefepime, cefpirome, and aztreonam. The enzyme implicated in this phenotype was a novel 180-kb plasmid-encoded TEM-type extended-spectrum beta-lactamase designated TEM-126 which harbors the mutations Asp179Glu and Met182Thr. TEM-126 exhibited significant hydrolytic activity (k(cat), 2 s(-1)) and a K(m) value of 82 muM against ceftazidime. Molecular dynamics simulations suggested that the substitution Asp179Glu induces subtle conformational changes to the omega loop which may favor the insertion of ceftazidime in the binding site and the correct positioning of the crucial residue Glu166. Overall, these results highlight the remarkable plasticity of TEM enzymes, which can expand their activity against ceftazidime by the addition of one carbon atom in the side chain of residue 179.
authors.affiliation: Faculté de Médecine, Centre Hospitalo-Universitaire, Clermont-Ferrand, France. julien.delmas@u-clermont1.fr
authors.forename: J
authors.initials: J
authors.lastname: Delmas
authors.forename: F
authors.initials: F
authors.lastname: Robin
authors.forename: F
authors.initials: F
authors.lastname: Bittar
authors.forename: C
authors.initials: C
authors.lastname: Chanal
authors.forename: R
authors.initials: R
authors.lastname: Bonnet
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001483:Base Sequence; D001665:Binding Sites; D002442:Ceftazidime / Q000494:pharmacology; D003227:Conjugation, Genetic; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics* / Q000302:isolation & purification; D018698:Glutamic Acid / Q000378:metabolism; D006868:Hydrolysis; D007525:Isoelectric Focusing; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017422:Sequence Analysis, DNA; D013912:Threonine / Q000378:metabolism; D001618:beta-Lactamases / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D013912:Threonine; D018698:Glutamic Acid; D002442:Ceftazidime; D001618:beta-Lactamases