Jeudi 16 octobre 2003
Nanometer-scale biomolecular motors utilize chemicalenergy and convert it to mechanical energy, i.e. forceand motion. Such motors are responsible for intra and extracellular motion, e.g. the movement of chromosomes during cell division. They take quantized center-of-mass steps of 8-37 nm, the exact step size depending on the motor.
How are these steps accomplished ? Do these motors walk or inchworm along ? To help answer this question, we have developed a new single molecule fluorescence technique with 1.5 nm spatial localization and sub-second temporal resolution. This exceeds the classical diffraction limit of light by 200-fold. A fluorophore is attached to the ’’foot’’ of a bipedal motor and the step size is measured. An inchworm model predicts a step size equal to the center of mass movement ; a walking model (’’foot over foot’’) predicts a step size twice the center of >mass movement.
We find the step size of Myosin V, an unconventional myosin involved in intracellular cargo transport is 74 nm +/- 3 nm, exactly twice the known center-of-mass step size of 37 nm.
We conclude Myosin V, and likely many other motors, move by walking.