1: Adv Exp Med Biol  1998;453:5-13; discussion 13-4 

Linear and rotary molecular motors.

Kinosita K Jr.

Department of Physics, Faculty of Science and Technology, Keio University,
Yokohama, Japan.

A single molecule of F1-ATPase has been shown to be the smallest rotary motor
ever found, with a central rotor of radius approximately 1 nm turning in a
stator barrel of radius approximately 5 nm. Continuous rotation of the central
gamma subunit was revealed under an optical microscope by attaching to gamma a
huge marker, an actin filament. In a separate study, rotation of a sliding actin
filament around its axis has been revealed by attaching a small probe, a single
fluorescent dye molecule, to the actin filament and detecting the orientation of
the fluorophore, and thus of the actin filament, through polarization imaging.
The axial rotation was slow compared to the linear sliding, indicating that
myosin does not 'walk' along the helical array of actin protomers but 'runs,'
skipping many protomers. The two motors above, one rotary and the other linear,
represent two extreme cases of the mode of motor operation: in the F1-ATPase the
two partners, the rotor and stator, never detach from each other whereas myosin
touches actin only occasionally. In considering the mechanisms of these and
other molecular motors, distinction between bending and binding is important.
The use of huge and small probes as described above should be useful in studies
of protein machines in general, as a means of detecting conformational changes
in a single protein molecule during function.

Publication Types:
Review
Review, Tutorial

PMID: 9889809 [PubMed - indexed for MEDLINE]