Inner membrane component of the type IV (T4S) secretion system that plays a role in surface and host cell adhesion, colonization, biofilm maturation, virulence, and twitching, a form of surface-associated motility. PilN/PilO heterodimers form the foundation of the inner-membrane PilM/PilN/PilO/PilP complex which plays an essential role in the assembly of a functional T4 pilus (PubMed:19857645). PilP connects PilO to the secretin PilQ. In turn, the PilM/PilN/PilO/PilP/PilQ complex facilitates transit of the pilus through the periplasm and clamps the pilus in the cell envelope (PubMed:23457250). Interacts with PilO, PilN and PilM (PubMed:19857645, PubMed:22053789). Interacts (via C-terminus) with the outer membrane secretin PilQ (PubMed:23457250). Deletion mutants lack surface pili.