FIGURE 5.

Single-bead force feedback optical trapping indicates a short step size for myosin X. A fascin-actin bundle is adhered to the coverslip surface, and a polystyrene bead conjugated to motor is lowered to the track and allowed to interact, leading to processive motions detected on a position detector. Shown are histograms of step size distributions determined using a step-finder algorithm (17) along a bundle. Positive values are fit to a Gaussian distribution. Two stepping regimes are separated by load. A, under a <0.6-pN load the motor takes 17.9 ± 0.3-nm steps. B, under loads >0.6 and <1 pN, myosin X takes shorter 12.3 ± 0.2-nm steps (±S.E.). See also supplemental Fig. S3.