Operation mechanism of rotary molecular motor F$_1$ probed by single-molecule techniques

F$_1$ is a rotary motor protein. Three catalytic $\beta $-subunits in the stator $\alpha_{3}\beta_{3}$ ring are torque generators, and rotate the rotor $\gamma $-subunit by sequential and cooperative conformational changes coupled with adenosine triphosphate (ATP) hydrolysis reaction. F$_1$ shows remarkable performances such as rotation rate faster than 10,000 rpm, high reversibility and efficiency in chemo-mechanical energy conversion. I will introduce basic characteristics of F$_1$ revealed by single-molecule imaging and manipulation techniques based on optical microscopy and high-speed atomic force microscopy. I will also discuss the possible operation mechanism behind the F$_1$, along with structurally-related hexameric ATPases, also mentioning the possibility of generating hybrid molecular motors.