Major component of the type IV pilus (T4P) that plays a role in surface and host cell adhesion, colonization, biofilm maturation, virulence, and twitching, a form of surface-associated motility facilitated by cycles of extension, adhesion, and retraction of T4P fibers. In addition, plays a critical role in type II secretion of exoenzymes by interacting with specific components such as XcpT or XcpU. Modulates host calcium signaling through interaction with host calcium-modulating cyclophilin ligand