title: Analysis of a carbapenem-hydrolyzing class A beta-lactamase from Enterobacter cloacae and of its LysR-type regulatory protein.
abstract: Carbapenems such as imipenem are extended-spectrum beta-lactam antibiotics, which are not hydrolyzed by the beta-lactamases commonly found in Enterobacteriaceae. Here we report a gene encoding a carbapenemase, which was cloned from the chromosome of a clinical isolate of Enterobacter cloacae, strain NOR-1, into pACYC184 plasmid in Escherichia coli. Unlike all the sequenced carbapenemases, which are class B metallo-beta-lactamases, the mature protein (NmcA) is a class A serine beta-lactamase. NmcA shares the highest amino acid identity (50%) with the extended-spectrum class A beta-lactamase MEN-1 from E. coli. In the opposite orientation from the nmcA promoter, an overlapping and divergent promoter was detected, along with an open reading frame, which encoded a 33.5-kDa protein (NmcR). The NmcR amino acid sequence displays homology with LysR-type transcriptional regulatory proteins, including the conserved residues near its N terminus within a helix-turn-helix motif. Deletion of nmcR resulted in decreased carbapenem resistance and a loss of beta-lactamase inducibility, demonstrating a positive role of NmcR in NmcA expression.
authors.affiliation: Abteilung Mikrobiologie, Biozentrum der Universität Basel, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Naas
authors.forename: P
authors.initials: P
authors.lastname: Nordmann
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D015780:Carbapenems / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004352:Drug Resistance, Microbial / Q000235:genetics; D016972:Enterobacter cloacae / Q000201:enzymology / Q000235:genetics*; D005786:Gene Expression Regulation; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D006868:Hydrolysis; D008969:Molecular Sequence Data; D015183:Restriction Mapping; D017421:Sequence Analysis; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D001618:beta-Lactamases / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D015780:Carbapenems; D014157:Transcription Factors; C073470:LysR protein, Bacteria; C088657:NmcA protein, Enterobacter cloacae; D001618:beta-Lactamases