Pil G may regulate asymmetric functioning of the T4a P system to allow for directional movement, while Fim V appears to localize both structural and regulatory elements—including the Pil SR two-component system—to cell poles for optimal function.
Type IV pili (T4P) are polar filamentous surface appendages made by a broad range of bacteria and archaea (1, 2).
However, of these three proteins, only Fim L is dispensable for twitching motility under c AMP-replete conditions.
Polar localization of the sensor kinase Pil S, a key regulator of transcription of the major pilin, was Fim V dependent.
However, unlike its homologues in other species that localize flagellar system components, Fim V was not required for swimming motility.
T4a P-mediated twitching motility requires both c AMP-dependent and -independent inputs (17, 31).
For example, provision of exogenous c AMP to mutants lacking Pil G restored piliation but not motility (17), and a mutant expressing a constitutively active form of Cya B but lacking Fim V failed to twitch (25).