Linear motor driven-rotary motion of a membrane-permeabilized ghost in Mycoplasma mobile

Mycoplasma mobile exhibits a smooth gliding movement as does its membrane-permeabilized ghost model. This exceptionally prominent experimental system has allowed us to conclude that the energy source for M. mobile motility is adenosine triphosphate (ATP), and the gliding is largely comprised of repetitions of unitary steps of about 70 nm. In the present study, we show a new motility mode, in which the ghost model prepared with a high concentration of detergent exhibits directed rotational motions with a constant speed. With a rotational speed and viscous friction of a single ghost, the torque was estimated to be [~]30 pN nm at saturated [ATP]s. Although the origin of the rotation has not been conclusively settled, we found that rotary ghosts treated with sialyllactose, the binding target for leg proteins, were stopped. This result suggested that biomolecules embedded on the cell membrane nonspecifically attaches to the glass and works as a flexible pivot point, and the linear motion of the leg is a driving force for a rotary motion. This simple geometry exemplifies the new mechanism, by which the movement of a linear motor is efficiently converted to a constant rotation of the object on a micrometer scale.