Motility of single one-headed kinesin molecules along microtubules

The motility of single one-headed kinesin molecules (K351 and K340), which were truncated fragments of Drosophila two-headed kinesin, has been tested using total internal reflection fluorescence microscopy. One-headed kinesin fragments moved continuously along the microtubules. The maximum distance traveled until the fragments dissociated from the microtubules for both K35 1 and K340 was similar to 600 nm. This value is considerably larger than th e space resolution of the measurement system (SID approximate to 30 nm). Al though the movements of the fragments fluctuated in forward and backward di rections, statistical analysis showed that the average movements for both K 340 and K351 were toward the plus end of the microtubules, i.e., forward di rection. When BDTC (a 1.3-S subunit of Propionibacterium shermanii transcar boxylase, which binds weakly to a microtubule), was fused to the tail (C-te rminus) of K351, its movement was enhanced, smooth, and unidirectional, sim ilar to that of the two-headed kinesin fragment, K411. However, the travel distance and velocity of K351 BDTC molecules were similar to3-fold smaller than that of K411. These observations suggest that a single kinesin head ha s basal motility, but coordination between the two heads is necessary for s tabilizing the basal motility for the normal level of kinesin processivity.