Type IV secretory pathway component VirB11, and related ATPases. The homohexamer, VirB11 is one of eleven Vir (virulence) proteins, which are required for T-pilus biogenesis and virulence in the transfer of T-DNA from the bacterial Ti (tumor-inducing)-plasmid into plant cells. The pilus is a fibrous cell surface organelle, which mediates adhesion between bacteria during conjugative transfer or between bacteria and host eukaryotic cells during infection. VirB11-related ATPases include Sulfolobus acidocaldarius FlaI, which plays key roles in archaellum (archaeal flagellum) assembly and motility functions, and the pilus assembly proteins CpaF/TadA and TrbB. This alignment contains the C-terminal domain, which is the ATPase.