Figure 20.

(a) Large optical probe measures rotation of kinesin proteins bound to microtubules. A 1.3 μm polystyrene bead bound to two smaller fluorescent beads is attached to the kinesin protein via a linker. Optical microscopy can distinguish changes in orientation of the two fluorescent beads. (b) Tracking angular rotation over time shows differences between two kinesin variants. (c) Variance in each single-molecule trace can be compiled to assess population behavior; the K351 variant exhibits a linear increase in variance, while the K448 variance can be fit asymptotically. Adapted from ref (247).