The SMR family: a novel family of multidrug efflux proteins involved with the efflux of lipophilic drugs

Mol Microbiol. 1996 Mar;19(6):1167-75. doi: 10.1111/j.1365-2958.1996.tb02462.x.


The sequenced members of a novel family of small, hydrophobic, bacterial multidrug-resistance efflux proteins, which we have designated the small multidrug resistance (SMR) protein family, are identified and analysed. Two distinct clusters of proteins were identified within this family: (i) small multidrug efflux systems; and (ii) Sug proteins, potentially involved in the suppression of groEL mutations. Hydropathy and residue distribution analyses of this family suggest a structural model in which the polypeptide chain spans the membrane four times as mildly amphipathic alpha-helices. The roles of specific residues, a possible mechanistic model of drug efflux, and the primary physiological role(s) of the SMR proteins are discussed.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Amino Acid Sequence
  • Antiporters*
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Biological Transport, Active
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Conserved Sequence
  • Drug Resistance, Multiple
  • Escherichia coli Proteins
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Peptides / chemistry
  • Peptides / metabolism
  • Phylogeny
  • Protein Structure, Secondary
  • Sequence Homology, Amino Acid


  • Antiporters
  • Bacterial Proteins
  • Carrier Proteins
  • Escherichia coli Proteins
  • Membrane Proteins
  • Peptides
  • EmrE protein, E coli

Associated data

  • GENBANK/L27430
  • GENBANK/M33479
  • GENBANK/M34831
  • GENBANK/M37889
  • GENBANK/M62732
  • GENBANK/X06151
  • GENBANK/X12868
  • GENBANK/X15574
  • GENBANK/X68232
  • GENBANK/X69949
  • GENBANK/Z11877