Pulling together with type IV pili.

Type IV pili are an efficient and versatile device for bacterial surface motility. They are widespread among the beta-, gamma-, and delta-proteobacteria and the cyanobacteria. Within that diversity, there is a core of conserved proteins that includes the pilin (PilA), the motors PilB and PilT, and various components of pilus biogenesis and assembly, PilC, PilD, PilM, PilN, PilO, PilP, and PilQ. Progress has been made in understanding the motor and the secretory functions. PilT is a motor protein that catalyzes pilus retraction; PilB may play a similar role in pilus extension. Type IV pili are multifunctional complexes that can act as bacterial virulence factors because pilus-based motility is used to spread pathogens over the surface of a tissue, or to build multicellular structures such as biofilms and fruiting bodies.