Crystal Structures of a Double-Barrelled Fluoride Channel

The Fluc family of fluoride channels is widespread among microorganisms, functioning to prevent the cytoplasmic accumulation of toxic fluoride ion. These channels possess a number of unusual features, including tremendous selectivity for F- over Cl- of at least 10,000-fold, and dual-topology, dimeric assembly. In order to understand the structural basis for ion selectivity, we solved crystal structures of two bacterial Fluc homologues to a maximum resolution of 2.1 A. These structures reveal that the Flucs actually possess two membrane-spanning pores - an unexpected double-barrelled architecture- and novel F- binding sites that include the quadrupolar edges of conserved phenylalanine rings.