Sodium binding is not required for fluoride channel Fluc dimerization but stabilizes the active state

To exhibit their various functions, ion channels need to faithfully assemble into the membrane. They must form stable structural scaffolds to support continuous, hydrophilic ion pathways and utilize mechanisms to link protein stability to selectivity, conductance, and gating. To better understand how ion channels balance stability and function, we studied the dimeric fluoride channel Fluc, a model system for interrogating equilibrium ion channel assembly in membranes. Single-molecule photobleaching and bulk FRET experiments demonstrate that wild-type Fluc is a long-lived dimer in membranes, in line with electrophysiological findings showing a high open probability around 95%.