Motor steps imaged in living cells

Molecular motors have been observed taking individual nanometer-sized steps in living cells, according to a new study. Using quantum-dot labeling methods and high-resolution bioimaging techniques, Harvard University chemists X. Sunney Xie, Xiaolin Nan, Peter A. Sims, and Peng Chen have tracked the motions of two types of molecular motors, kinesin and dynein, and have observed the proteins shuttling in opposite directions along microtubules in discrete 8-nm steps (J. Phys. Chem. B 2005, 109, 24220). The investigation, which exploits the 300-microsecond and 1.5-nm time and spatial resolution of the video imaging technique, reveals that the motor proteins also move by way of 16-nm and occasionally 24-nm steps, which may be indicative of multiple molecules acting in unison, the team suggests. The study broadens understanding of cellular transport mechanisms and demonstrates that quantum-dot methods are suitable for probing single-molecule events in living cells under physiological conditions.