Pilt

PilT is an ATPase enzyme that powers the retraction of type IV pili (T4P) in many bacteria. Encoded by pilT in the pil operon, it belongs to the PilT_NTPase family of P-loop NTPases within the broader AAA+ superfamily. PilT functions in concert with other pilus assembly components to toggle pili between extended and retracted states, enabling surface-associated behaviors.

PilT operates as a hexameric ring that binds and hydrolyzes ATP at its active sites. The energy from ATP hydrolysis drives conformational changes that pull the pilus filament back into the cell, producing retraction. In several species, a second retraction ATPase, PilU, can enhance retraction under load or compensate when PilT activity is reduced. The pilus base is formed by a multi-protein complex including inner-membrane components that interface with the cytoplasmic PilT motor.

Genetically, pilT is commonly co-located with other pilus genes such as pilB (assembly ATPase) and pilA (pilin subunit). Expression and activity of PilT are regulated by environmental cues and regulatory networks that coordinate pilus assembly, retraction, and surface behaviors. Mutations that abolish PilT function typically yield non-retractile pili, impaired twitching motility, and altered biofilm formation or virulence.

PilT-mediated retraction is important for twitching motility, DNA uptake during natural transformation, and host interactions in several pathogens, including Pseudomonas aeruginosa and Neisseria species. Structural and biochemical studies have illuminated its hexameric architecture and nucleotide-dependent conformational changes, contributing to a broader understanding of type IV pilus dynamics.