Parallel topology of genetically fused EmrE homodimers

Sonia Steiner-Mordoch, Misha Soskine, Dalia Solomon, Dvir Rotem, Ayala Gold, Michal Yechieli, Yoav Adam, Shimon Schuldiner*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


EmrE is a small H+-coupled multidrug transporter in Escherichia coli. Claims have been made for an antiparallel topology of this homodimeric protein. However, our own biochemical studies performed with detergent-solubilized purified protein support a parallel topology of the protomers. We developed an alternative approach to constrain the relative topology of the protomers within the dimer so that their activity can be assayed also in vivo before biochemical handling. Tandem EmrE was built with two identical monomers genetically fused tail to head (C-terminus of the first to N-terminus of the second monomer) with hydrophilic linkers of varying length. All the constructs conferred resistance to ethidium by actively removing it from the cytoplasm. The purified proteins bound substrate and transported methyl viologen into proteoliposomes by a proton-dependent mechanism. A tandem where one of the essential glutamates was replaced with glutamine transported only monovalent substrates and displayed a modified stoichiometry. The results support a parallel topology of the protomers in the functional dimer. The implications regarding insertion and evolution of membrane proteins are discussed.

Original languageAmerican English
Pages (from-to)17-26
Number of pages10
JournalEMBO Journal
Issue number1
StatePublished - 9 Jan 2008


  • Ion-coupled transport
  • Membrane protein evolution
  • Membrane protein structure
  • Membrane protein topology
  • Multidrug transporters


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