Figure 1. Schematic of the T4P machinery in T. thermophilus.
The type IV pilus machinery is a heterooligomer, formed from at least 10 different proteins. The PilQ secretin (orange) forms a channel in the outer membrane for secretion of the pilus-forming protein PilA4 (green), which is processed by the prepillin peptidase PilD (grey) (Friedrich et al., 2002; Schwarzenlander et al., 2009). The membrane protein PilW (light orange) plays a role in DNA transport, PilQ assembly, and pilus extrusion (Rumszauer et al., 2006; Schwarzenlander et al., 2009). The dimeric complex PilC (red) is located in the inner membrane and is essential for pilus formation (Friedrich et al., 2002; Karuppiah et al., 2010). PilM (light brown), PilN (dark brown), and PilO (beige) are suggested to form the inner membrane assembly platform and connect the periplasmic and cytoplasmic sides of the complex (Rumszauer et al., 2006; Schwarzenlander et al., 2009; Karuppiah and Derrick, 2011; Karuppiah et al., 2013). The cytoplasmic ATPases PilF (bright yellow) and PilT1/PilT2 (pale yellow) drive pilus extension and retraction, respectively (indicated with red arrows) (Rose et al., 2011; Salzer et al., 2014b).