Functional interactions of VirB11 traffic ATPases with VirB4 and VirD4 molecular motors in type IV secretion systems.

Pilus biogenesis and substrate transport by type IV secretion systems require energy, which is provided by three molecular motors localized at the base of the secretion channel. One of these motors, VirB11, belongs to the superfamily of traffic ATPases, which includes members of the type II secretion system and the type IV pilus and archaeal flagellar assembly apparatus. Here, we report the functional interactions between TrwD, the VirB11 homolog of the conjugative plasmid R388, and TrwK and TrwB, the motors involved in pilus biogenesis and DNA transport, respectively.

Autoinhibitory regulation of TrwK, an essential VirB4 ATPase in type IV secretion systems.

Type IV secretion systems (T4SS) mediate the transfer of DNA and protein substrates to target cells. TrwK, encoded by the conjugative plasmid R388, is a member of the VirB4 family, comprising the largest and most conserved proteins of T4SS. In a previous work we demonstrated that TrwK is able to hydrolyze ATP.

Functional dissection of the conjugative coupling protein TrwB.

The conjugative coupling protein TrwB is responsible for connecting the relaxosome to the type IV secretion system during conjugative DNA transfer of plasmid R388. It is directly involved in transport of the relaxase TrwC, and it displays an ATPase activity probably involved in DNA pumping. We designed a conjugation assay in which the frequency of DNA transfer is directly proportional to the amount of TrwB.

ATPase activity and oligomeric state of TrwK, the VirB4 homologue of the plasmid R388 type IV secretion system.

Type IV secretion systems (T4SS) mediate the transfer of DNA and protein substrates to target cells. TrwK, encoded by the conjugative plasmid R388, is a member of the VirB4 family, comprising the largest and most conserved proteins of T4SS. VirB4 was suggested to be an ATPase involved in energizing pilus assembly and substrate transport.

The ATPase activity of the DNA transporter TrwB is modulated by protein TrwA: implications for a common assembly mechanism of DNA translocating motors.

Conjugative systems contain an essential integral membrane protein involved in DNA transport called the Type IV coupling protein (T4CP). The T4CP of conjugative plasmid R388 is TrwB, a DNA-dependent ATPase. Biochemical and structural data suggest that TrwB uses energy released from ATP hydrolysis to pump DNA through its central channel by a mechanism similar to that used by F1-ATPase or ring helicases.