VirB5 protein familyThis family contains VirB5 domains, including TraC, a VirB5 homolog encoded by the pKM101 plasmid, and similar proteins. VirB5 is one of 11 conserved proteins (VirB1-VirB11) in Agrobacterium tumefaciens, the causative agent of crown gall disease, that span the inner and the outer membrane, and is involved in type IV DNA secretion systems (T4SS) which mediate the translocation of virulence factors (proteins and/or DNA) from Gram-negative bacteria into eukaryotic cells. VirB5 assembles extracellular pili by interacting with several essential proteins. VirB2-VirB5 complex formation precedes incorporation into pili; it depends on the inner membrane protein VirB4 to interact directly with and stabilize VirB8 in order for VirB5 to bind to VirB8 and VirB10. Mutagenesis studies show that VirB5 proteins participate in protein-protein interactions important for pilus assembly and function.