flaI

FlaI is an ATPase protein that forms part of the archaeal flagellum, or archaellum, assembly system. It is an essential cytoplasmic component that uses energy from ATP hydrolysis to power the assembly of the archaellum filament and, in some models, to drive motor activity. FlaI belongs to the AAA+ family of ATPases and shows sequence similarity to bacterial PilB-like motors that power type IV pili, reflecting a conserved mechanism for assembling surface structures in prokaryotes.

In many archaea, FlaI functions as a hexameric motor that coordinates with other components of the archaellum complex. Its activity is thought to be regulated by interacting factors such as FlaH and by associations with membrane-anchored proteins that form the base of the motor. The exact details of the energy transduction pathway—whether ATP hydrolysis directly powers rotation, assembly, or both—remain an area of active research, but FlaI is consistently implicated as a central driver of archaellum biogenesis.

Genetically, the flaI gene is typically located within the archaeal archaellum gene cluster, alongside other fla genes such as flaH and flaJ. Its presence is widely conserved among archaeal lineages that possess archaella, underscoring its essential role in motility. Across species, FlaI retains the core AAA+ ATPase domain, though sequence variation exists, reflecting differences in regulation and interaction partners among diverse archaea.

Overall, FlaI is a key component of the archaeal motility apparatus, central to assembling and possibly powering the archaellum through ATP-driven conformational changes within the motor complex.