3.A.6.2.1
Flagellar protein export system.  Infrequent ATP hydrolysis by the FliI₆FliJ ring is sufficient for gate activation, allowing processive translocation of export flagellar protein substrates for efficient flagellar assembly (Minamino et al. 2014). FliO has been identified as a flagellar basal body chaparone protein (Fabiani et al. 2017). The flagellar protein export apparatus switches its substrate specificity when hook length has reached approximately 55 nm, and the hydrophilic C-terminal domain of FlhB is involved in this switching process (Inoue et al. 2019).