Cooperative binding of kinesin to the microtubule in the presence of ATP
Interaction of kinesin-coated latex beads with a single microtubule was directly observed by fluorescence microscopy. In the presence of ATP, binding of a kinesin bead to the microtubule facilitated the subsequent binding of other kinesin beads to an adjacent region on the microtubule that extended for micrometers in length (Fig. A, Video). This cooperative binding was not observed in the presence of ADP or AMP-PNP, where binding along the microtubule was random.
Long-range cooperative binding of kinesin-coated beads along a microtubule
Cooperative binding could also be induced by the engineered, heterodimeric kinesin, WT/E236A. This kinesin could hydrolyze ATP but would remain fixed on the microtubule in the presence of ATP. Wild-type kinesin bound preferentially in close proximity to the stationary WT/E236A kinesin on a microtubule (Fig. C, indicated by an arrow head), but their binding was biased to the plus-end direction (Fig. D).
These results suggest that kinesin binding and ATP hydrolysis may cause a long-range state transition in the microtubule, increasing its affinity for kinesin towards its plus end (Fig. B). Our study highlights the active involvement of microtubules in kinesin motility.