Myosin-V is a mechanical ratchet

Gebhardt et al. 10.1073/pnas.0510191103.

Supporting Information

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Supporting Figure 5
Supporting Figure 6
Supporting Text
Supporting Figure 7

Fig. 5. Sample trace of a myosin-V molecule under different backward forces at 1 µM ATP. The motor steps processively backward under 3-pN superstall load. After the load has been lowered to substall conditions (1 pN), the molecule resumes forward motion, hence demonstrating correct function.

Supporting Figure 6

Fig. 6. Examples of processive myosin-V backward stepping at 5- and 10-pN backward loads and various ATP concentrations. The time scale was chosen different for the two forces to account for the different kinetics.

Supporting Figure 7

Fig. 7. Sample trace of a myosin-V molecule under 3-pN backward load at 1 µM ATP. After an additional sideward force of 8 pN has been applied the motor is still able to step backward processively. This observation supports a hand-over-hand stepping model of backward steps and rules out detachment and rapid reattachment of the whole molecule as a model for backward stepping. Under these conditions the bead would be pulled rapidly towards the trap center and hence off the filament if the motor detached simultaneously with both heads. The jump in the trace occurring upon application of the sideward force is due to corrections for the changed angle between myosin-V and actin.