Germanium nanospheres for ultraresolution picotensiometry of kinesin motors

Kinesin motors are essential for transport of cellular cargo along cytoskeletal microtubule filaments. How motors step, detach, and cooperate is still unclear. To dissect the molecular motion of kinesin-1, we have developed germanium nanospheres as ultraresolution optical trapping probes. We found that single motors took 4-nm-center-of-mass steps. Furthermore, motors never detached from microtubules under native hindering load conditions. Instead, motors slid on microtubules with microsecond-long, 8-nm steps and remained in this slip state before detaching or reengaging in directed motion. Surprisingly, reengagement and, thus, rescue of directed motion was prevailing. We argue that teams of motors may be synchronized through this slip state and rescues need to be accounted for to understand long-range transport. One Sentence SummaryOptical trapping of high-refractive-index semiconductor nanoparticles shows how motors detach and walk with 4-nm steps.