Crystal Structure of Fluc, a Microbial Fluoride Channel

Widespread bacteria, archaea, unicellular eukaryotes, and plants possess fluoride channels, called Flucs, to export toxic environmental fluoride anion from the cytoplasm. These proteins conduct F- ion at ∼10 pS, are >10,000-fold selective for fluoride over chloride, and are constructed as extremely unusual antiparallel dimers. Here, we present the x-ray crystal structure of a Fluc channel from Bordetella pertussis, in complex with a pore-blocking FN3 domain “monobody.” The structure reveals a closed conformation of the protein with the predicted antiparallel architecture and an occluded hourglass-shaped pore at the subunit interface.