pilNOPQ

pilNOPQ refers to a conserved set of genes encoding key components of the Type IV pilus assembly machinery in many Gram-negative bacteria. The gene cluster commonly includes pilN, pilO, pilP, and pilQ, which together form the core bridge between the inner and outer membranes to facilitate pilus assembly and extrusion. The operon organization is often part of a larger pil gene cluster that also includes genes encoding the cytoplasmic ATPases and other assembly factors.

PilN and PilO are inner membrane proteins with substantial periplasmic domains that form a heteromeric complex. PilP is a periplasmic lipoprotein anchored to the inner membrane, stabilizing the PilN–PilO complex and mediating interactions with PilQ. PilQ is an outer membrane secretin that assembles into a gated pore through which the pilus fiber is extended and retracted. The PilNPOQ assembly acts as an alignment and stabilization scaffold that couples the cytoplasmic ATPase activity (for pilus extension and retraction) to the outer membrane pore.

Functionally, the PilN, PilO, PilP, and PilQ proteins are essential for proper pilus formation and surface-associated behaviors such as twitching motility and adherence. Disruption of any component often abolishes pilus assembly, reducing motility and biofilm formation. The PilNPOQ complex is highly conserved among bacteria that utilize Type IV pili and related secretion systems, reflecting its fundamental role in secretin-assisted pilus biogenesis and secretion.