Structure of the transcriptional regulator LmrR and its mechanism of multidrug recognition

EMBO J. 2009 Jan 21;28(2):156-66. doi: 10.1038/emboj.2008.263. Epub 2008 Dec 18.

Abstract

LmrR is a PadR-related transcriptional repressor that regulates the production of LmrCD, a major multidrug ABC transporter in Lactococcus lactis. Transcriptional regulation is presumed to follow a drug-sensitive induction mechanism involving the direct binding of transporter ligands to LmrR. Here, we present crystal structures of LmrR in an apo state and in two drug-bound states complexed with Hoechst 33342 and daunomycin. LmrR shows a common topology containing a typical beta-winged helix-turn-helix domain with an additional C-terminal helix involved in dimerization. Its dimeric organization is highly unusual with a flat-shaped hydrophobic pore at the dimer centre serving as a multidrug-binding site. The drugs bind in a similar manner with their aromatic rings sandwiched in between the indole groups of two dimer-related tryptophan residues. Multidrug recognition is facilitated by conformational plasticity and the absence of drug-specific hydrogen bonds. Combined analyses using site-directed mutagenesis, fluorescence-based drug binding and protein-DNA gel shift assays reveal an allosteric coupling between the multidrug- and DNA-binding sites of LmrR that most likely has a function in the induction mechanism.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Benzimidazoles / chemistry*
  • Daunorubicin / chemistry*
  • Dimerization
  • Helix-Turn-Helix Motifs
  • Hydrogen Bonding
  • Lactococcus lactis / metabolism*
  • Models, Molecular*
  • Molecular Sequence Data
  • Protein Binding
  • Protein Conformation
  • Transcription, Genetic

Substances

  • Bacterial Proteins
  • Benzimidazoles
  • bisbenzimide ethoxide trihydrochloride
  • Daunorubicin

Associated data

  • PDB/3F8B
  • PDB/3F8C
  • PDB/3F8F