Single-molecule tracking of myosins with genetically engineered amplifier domains.

We combined protein engineering and single molecule measurements to directly record the step size of a series of myosin constructs with shortened and elongated artificial neck domains. Our results show that the step size has a clear linear dependence on the length of the neck domain and we also established that mechanical amplification in the myosin motor is based on a rotation of the neck domain relative to the actin-bound head. For all our constructs, including those with artificial necks, the magnitude of the neck rotation concurrent with the displacement step was approximately 30 degrees. The engineered change in the step size of myosin marks a significant advance in our ability to selectively modify the functional properties of molecular motors.