Analysis of a carbapenem-hydrolyzing class A beta-lactamase from Enterobacter cloacae and of its LysR-type regulatory protein

Proc Natl Acad Sci U S A. 1994 Aug 2;91(16):7693-7. doi: 10.1073/pnas.91.16.7693.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / genetics*
  • Base Sequence
  • Carbapenems / metabolism*
  • DNA Mutational Analysis
  • Drug Resistance, Microbial / genetics
  • Enterobacter cloacae / enzymology
  • Enterobacter cloacae / genetics*
  • Gene Expression Regulation*
  • Gene Expression Regulation, Bacterial
  • Gene Expression Regulation, Enzymologic
  • Hydrolysis
  • Molecular Sequence Data
  • Restriction Mapping
  • Sequence Analysis
  • Sequence Deletion
  • Sequence Homology, Amino Acid
  • Transcription Factors / genetics*
  • Transcription, Genetic
  • beta-Lactamases / genetics*


  • Bacterial Proteins
  • Carbapenems
  • Transcription Factors
  • LysR protein, Bacteria
  • NmcA protein, Enterobacter cloacae
  • beta-Lactamases

Associated data

  • GENBANK/Z21956