piln

PilN is a component of the type IV pilus assembly machinery found in many Gram-negative bacteria. It is part of the PilMNPQ subcomplex that coordinates the assembly and retraction of type IV pili, enabling processes such as surface attachment and twitching motility. In most species, PilN is a bitopic inner membrane protein with a short cytoplasmic region, a single transmembrane helix, and a periplasmic domain that engages in protein–protein interactions. PilN commonly forms a heterodimer with PilO, and together with PilM and PilP helps establish a stable alignment platform that connects the cytoplasmic ATPase PilB to the outer membrane secretin PilQ.

Genetic organization and function: pilN is often located within the pilMNOP operon. Loss-of-function mutations typically impair pilus assembly, resulting in defective twitching motility, reduced surface adhesion, and, in naturally competent bacteria, diminished DNA uptake. Through its interactions with PilM, PilO, and PilP, PilN contributes to proper localization and stability of the pilus assembly machinery at the cell envelope.

Biological significance: Type IV pili mediate attachment to biotic and abiotic surfaces, microcolony formation, and social motility. Consequently, PilN supports these processes and can influence virulence traits in certain pathogens by facilitating colonization and biofilm development. Conservation and variation: PilN is broadly conserved among bacteria that encode type IV pili, though sequence variation reflects species-specific adaptations.

Research context: Model-system studies in organisms such as Pseudomonas aeruginosa and Neisseria gonorrhoeae have elucidated its role within the assembly complex and its interactions with other components. Ongoing work aims to define the precise conformational changes and dynamics of PilN during pilus extension and retraction.