The type IV pilus and type II secretion systems are structurally related and are likely evolved from a common ancestor. Both have a an outer membrane secretin protein (PilQ and XcpQ), an inner membrane platform protein (PilC or XcpS) and share the PilD/XcpA prepilin peptidase protein. Both have a major subunit (PilA or XcpT) with participation from minor pilin-like proteins specific to each system. Other similarities include the requirement for inner membrane associated proteins (PilM, PilN, PilO or XcpY, XcpZ). One notable difference is the presence of only a single ATPase, XcpR, in the T2S system, while the T4P system has 3 separate ATPases, PilB, PilT and PilU. The T2S system also lacks a PilF homologue.
Instead of extending and retracting to cause motility like the type IV pilus, the short T2S “pseudopilus” is thought to act as a piston, releasing proteins from the periplasm to the exterior environment of the cell.
We are interested in identifying new points of intersection between these systems, since such components would represent ideal targets for interventions affecting multiple virulence attributes. We have evidence that modulating the levels of the minor pilins of the T4P system affect T2S, as does mutation of the large FimV protein.