PilT : a motor on steroids

Many gram-negative bacteria, including the human pathogen that causes gonorrhea, use type IV pili for attachment to host cells. Retraction of the pilus is strong enough to propel a bacterium along cells. Berenike Maier, Michael Sheetz (Columbia University, New York, NY), and colleagues have now measured just how much force is released by pilus retraction, a process known to require the PilT ATPase. Their findings make PilT the strongest known molecular motor.The strength of pilus retraction was measured by its ability to pull an attached bead from a laser trap of varying stiffness. Retraction frequency was proportional to PilT concentration, indicating that PilT is the molecular motor powering retraction. The retraction of one pilus generated forces in excess of 100 pN, between 2 and 20 times that released by...