Science 333, 755–758 (2011)

F1-ATPase is a rotary motor protein driven by adenosine triphosphate (ATP) with a central rotor that turns in a stator ring. The stator is a catalytic hexameric ring in which three of the subunits can sequentially undergo conformational changes on ATP hydrolysis to rotate the central shaft unidirectionally. The structure of the motor protein has been carefully characterized, and the rotation of the central shaft has been directly observed using fluorescent probes and video microscopy. However, the exact structural basis of the unidirectional motion remains unclear. Toshio Ando, Hiroyuki Noji and colleagues have now used high-speed atomic force microscopy to image the conformational changes in a rotorless F1-ATPase.

The researchers — who are based at Kanazawa University, Osaka University and the University of Tokyo — covalently attached isolated stator rings to a mica surface and imaged them with a frame capture time of around 80 ms. In the three active subunits of the stator, conformational states were seen to propagate cyclically around the ring in an anticlockwise direction, which is similar to the known rotation of the rotary shaft. The rate of rotation was lower than that when the shaft is attached, but the results illustrate that cooperativity between the subunits is intrinsic to the stator ring.