Effects of external strain on the regulation of microtubule sliding induced by outer arm dynein of sea urchin sperm flagella.

Oscillatory bending movement of eukaryotic flagella is powered by orchestrated activity of dynein motor proteins that hydrolyse ATP and produce microtubule sliding. Although the ATP concentration within a flagellum is kept uniform at a few millimoles per litre level, sliding activities of dyneins are dynamically coordinated along the flagellum in accordance with the phase of bending waves. Thus at the organellar level the dynein not only generates force for bending but also modulates its motile activity by responding to bending of the flagellum. Single molecule analyses have suggested that dynein at the molecular level, even if isolated from the axoneme, could alter the modes of motility in response to mechanical strain. However, it still remains unknown whether the coordinated activities of multiple dyneins can be modulated directly by mechanical signals. Here, we studied the effects of externally applied strain on the sliding movement of microtubules interacted with an ensemble of dynein molecules adsorbed on a glass surface. We found that by bending the microtubules with a glass microneedle, three modes of motility that have not been previously characterized without bending can be induced: stoppage, backward sliding and dissociation. Modification in sliding velocities was also induced by imposed bending. These results suggest that the activities of dyneins interacted with a microtubule can be modified and coordinated through external strain in a quite flexible manner, and that such a regulatory mechanism may be the basis of flagellar oscillation.