Structural and functional study of the phenicol-specific efflux pump FloR belonging to the major facilitator

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Martine Braibant1, Jacqueline Chevalier, Elisabeth Chaslus-Dancla

  • 1UR86 Bio-Agresseurs, Santé, Environnement, Institut National de la Recherche Agronomique, Centre de Recherche de Tours, 37380 Nouzilly, France.

Antimicrobial Agents and Chemotherapy
|June 28, 2005
PubMed

Insights

The Salmonella enterica floR gene encodes a transporter protein that exports phenicol drugs like florfenicol and chloramphenicol. This efflux mechanism is crucial for bacterial resistance, involving specific amino acids for drug recognition and transporter function.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Biochemistry

Background:

  • The florfenicol-chloramphenicol resistance gene (floR) from Salmonella enterica was previously identified.
  • FloR was postulated to belong to the major facilitator (MF) superfamily of drug exporters.

Purpose of the Study:

  • To confirm the transmembrane topological model of FloR.
  • To classify FloR within the MF efflux transporter families.
  • To elucidate the functional mechanism and key residues involved in FloR's drug efflux activity.

Main Methods:

  • PhoA gene fusion method to confirm transmembrane topology.
  • Site-directed mutagenesis to identify essential amino acid residues.
  • Analysis of substrate specificity and energy dependence (proton motive force).

Main Results:

  • Confirmed FloR as a member of the DHA12 family, possessing 12 transmembrane domains.
  • Demonstrated FloR's specificity for phenicol drugs (chloramphenicol, florfenicol, thiamphenicol).
  • Identified essential residues D23 (TMS1) and R109 (TMS4) for active efflux, with D23 likely involved in drug recognition.
  • Identified E283 (TMS9) as crucial for proper membrane folding of the transporter.

Conclusions:

  • FloR functions as an active efflux transporter utilizing proton motive force.
  • Specific charged residues, particularly D23, are critical for phenicol drug binding and transport.
  • Understanding FloR's mechanism provides insights into antibiotic resistance in bacteria.

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