Pilu

PilU is a bacterial protein that participates in the retraction of type IV pili, a process powered by ATP hydrolysis. It is considered a PilT-like ATPase and typically works in conjunction with PilT to facilitate pilus retraction. PilU is not usually required for pilus assembly, which is driven by other components in the pilus biogenesis system, but it contributes to efficient retraction and pilus dynamics, especially under higher mechanical load.

In many bacteria, the gene encoding PilU is located near pilT, and the two genes are often co-transcribed in an operon, reflecting coordinated regulation of pilus retraction. PilU proteins are cytoplasmic and possess conserved nucleotide-binding motifs characteristic of P-loop ATPases, sharing sequence similarity with PilT. Structural and functional studies in various species suggest that PilU can form part of the retraction motor complex and may influence the rate or force of retraction, though the exact interactions can vary among organisms.

Type IV pili are surface fibers involved in adhesion, twitching motility, biofilm formation, and competence for DNA uptake. By contributing to pilus retraction, PilU affects these processes indirectly through its role in pilus dynamics. The presence and importance of PilU can differ across bacterial species, with some relying more heavily on PilT alone and others requiring PilU for full retraction efficiency.

See also: Type IV pilus, PilT, PilB.