Fig 4.

Optical trapping nanometry for measurement of stall force. (a) Representative traces of the displacement of kinesin-coated beads along a MT. The displacement of the bead and the corresponding force are indicated on the left. For WT/L12 and L12/L12, the scale of displacement is different, because a weaker trap stiffness was used (0.007 pN/nm, instead of 0.032 pN/nm used for others). Applied force is shown on the same scale but the time scale is different in each trace. In the case of L12/L12, a higher concentration of kinesin (1–2 μM instead of 5–50 nM) was needed to observe any attachment signals (reduced vibration, as indicated by the solid line). In this case, more than one molecule is expected to be involved. (b) The force–velocity relationships of the WT kinesin (black, filled triangle), WT/L8 (blue, filled square), L8/L8 (blue, open square), WT/L11 (green, filled diamond), L11/L11 (green, open diamond), WT/L12 (red, filled circle), and L12/L12 (red, open circle). Solid lines represent the best fit of the data, and the y axis and x axis show the maximum velocity and the stall force, respectively.