On parallel and antiparallel topology of a homodimeric multidrug transporter.

The recently suggested antiparallel topology of EmrE has intriguing implications for many aspects of the biology of ion-coupled transporters. However, it is at odds with biochemical data that demonstrated the same topology for all protomers in the intact cell and with extensive cross-linking studies. To examine this apparent contradiction we chemically cross-linked dimers with a rigid bifunctional maleimide using Cys replacements at positions not permissible by an antiparallel topology.