Myosin I can act as a molecular force sensor

The ability to sense molecular tension is crucial for a wide array of cellular processes, including the detection of auditory stimuli, control of cell shape, and internalization and transport of membranes. We show that myosin I, a motor protein that has been implicated in powering key steps in these processes, dramatically alters its motile properties in response to tension. We measured the displacement generated by single myosin I molecules, and we determined the actin-attachment kinetics with varying tensions using an optical trap. The rate of myosin I detachment from actin decreases > 75- fold under tension of 2 piconewtons or less, resulting in myosin I transitioning from a low (< 0.2) to a high (> 0.9) duty- ratio motor. This impressive tension sensitivity supports a role for myosin I as a molecular force sensor.