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 ∼30°. 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.