PilTmediated

PilT-mediated pilus retraction refers to the retraction of type IV pili powered by the PilT ATPase, a central motor in many bacterial pilus systems. PilT functions as a hexameric AAA+ ATPase that couples ATP hydrolysis to mechanical work, withdrawing pilus fibers from the cell surface.

In most organisms, pilus extension is driven by the PilB ATPase at the same assembly site, while retraction is driven by PilT; in some species the PilU protein acts as a co-regulating or supporting ATPase to enhance retraction. Hydrolysis of ATP by PilT triggers conformational changes within the pilus base, disassembling pilin subunits and pulling the filament inward. Retraction enables twitching motility and can power DNA uptake during competence in naturally transformable bacteria.

Biological roles of PilT-mediated retraction include twitching motility, surface adhesion, microcolony formation, and biofilm development. In pathogenic bacteria, pilus retraction contributes to colonization, tissue interaction, and immune evasion, influencing infection dynamics and virulence. The rapid cycling of extension and retraction allows bacteria to explore surfaces and respond to environmental cues.

Structure and regulation: PilT is encoded within pilus operons and commonly forms hexameric rings. It contains conserved Walker A and B motifs typical of AAA+ ATPases, with activity tied to nucleotide binding and hydrolysis. Structural and biochemical studies reveal distinct conformational states corresponding to ATP- or ADP-bound forms. PilT interacts with the core assembly complex, including PilC, PilM, PilN, PilO and PilQ, coordinating retraction with pilus assembly. In some systems, PilU modulates retraction dynamics by altering motor force and speed.

Research and clinical relevance: Understanding PilT-mediated retraction clarifies bacterial surface motility, biofilm development, and pathogenic strategies, and may inform approaches to disrupt pilus function in antimicrobial development.