Three-dimensional optical tweezers tracking resolves random sideward steps of the kinesin-8 Kip3

The budding yeast kinesin-8 Kip3 is a highly processive motor protein that walks to the ends of cytoskeletal microtubules and shortens them in a collective manner. However, how exactly Kip3 reaches the microtubule end is unclear. While rotations of microtubules in multimotored Kip3 gliding assays implied directed sideward switching between microtubule protofilaments, two-dimensional (2D), single-molecule, optical-tweezers assays indicated that Kip3 randomly switched protofilaments. Here, we topographically suspended microtubules such that Kip3 motors could freely access the microtubules in 3D.

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