Single-molecule tracking of myosins with genetically engineered amplifier domains

We combined protein engineering and single molecule measurements to directl y 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 esta blished that mechanical amplification in the myosin motor is based on a rot ation of the neck domain relative to the actin-bound head. for all our cons tructs, including those with artificial necks, the magnitude of the neck ro tation concurrent with the displacement step was similar to 30 degrees. The engineered change in the step size of myosin marks a significant advance i n our ability to selectively modify the functional properties of molecular motors.