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, PubMed:19857646). In turn, associates with PilM and facilitates PilM functionally relevant structural changes (PubMed:27022027). Homodimer (PubMed:27474743). Interacts with PilO (PubMed:19857645, PubMed:19857646, PubMed:22053789, PubMed:27474743). Interacts with PilP (via N-terminus) (PubMed:22053789). Interacts (via N-terminus) with PilM; this interaction modulates PilM ATP binding site (PubMed:19857646, PubMed:27022027). Deletion mutants lack surface pili.