A common binding site for substrates and protons in EmrE, an ion-coupled multidrug transporter

FEBS Lett. 2000 Jun 30;476(1-2):93-7. doi: 10.1016/s0014-5793(00)01677-x.


EmrE is an Escherichia coli 12-kDa multidrug transporter, which confers resistance to a variety of toxic cations by removing them from the cell interior in exchange with two protons. EmrE has only one membrane-embedded charged residue, Glu-14, that is conserved in more than 50 homologous proteins and it is a simple model system to study the role of carboxylic residues in ion-coupled transporters. We have used mutagenesis and chemical modification to show that Glu-14 is part of the substrate binding site. Its role in proton binding and translocation was shown by a study of the effect of pH on ligand binding, uptake, efflux and exchange reactions. We conclude that Glu-14 is an essential part of a binding site, common to substrates and protons. The occupancy of this site is mutually exclusive and provides the basis of the simplest coupling of two fluxes.

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

  • Animals
  • Antiporters / chemistry*
  • Antiporters / metabolism*
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism*
  • Binding Sites
  • Carrier Proteins / chemistry
  • Carrier Proteins / metabolism*
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins
  • Membrane Proteins / chemistry*
  • Membrane Proteins / metabolism*
  • Models, Molecular
  • Protein Conformation


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