Kinesin Walks Hand-Over-Hand

TLDR

Kinesin is a processive motor that takes 8.3‑nm steps along microtubules per ATP, and the debate over whether it moves by a hand‑over‑hand or inchworm mechanism has persisted. The authors labeled one kinesin head with Cy3 and localized its position to within 2 nm before and after each step. The data show that kinesin heads step 17.3 ± 3.3 nm, alternating 17‑nm and 0‑nm steps, strongly supporting a hand‑over‑hand mechanism with both heads bound to the microtubule while awaiting ATP.

Abstract

Kinesin is a processive motor that takes 8.3-nm center-of-mass steps along microtubules for each adenosine triphosphate hydrolyzed. Whether kinesin moves by a "hand-over-hand" or an "inchworm" model has been controversial. We have labeled a single head of the kinesin dimer with a Cy3 fluorophore and localized the position of the dye to within 2 nm before and after a step. We observed that single kinesin heads take steps of 17.3 +/- 3.3 nm. A kinetic analysis of the dwell times between steps shows that the 17-nm steps alternate with 0-nm steps. These results strongly support a hand-over-hand mechanism, and not an inchworm mechanism. In addition, our results suggest that kinesin is bound by both heads to the microtubule while it waits for adenosine triphosphate in between steps.