Ratchetlike properties of in vitro microtubule translocation by a Chlamydomonas inner-arm dynein species c in the presence of flow.

To investigate the force generation properties of Chlamydomonas axonemal inner-arm dyneins in response to external force, we analyzed microtubule gliding on dynein-coated surfaces under shear flow. When inner-arm dynein c was used, microtubule translocation in the downstream direction accelerated with increasing flow speed in a manner that depended on the dynein density and ATP concentration. In contrast, the microtubule translocation velocity in the upstream direction was unaffected by the flow speed. The number of microtubules on the glass surface was almost constant with and without flow, suggesting that gliding acceleration was not simply caused by weakened dynein-microtubule binding. With other inner-arm dynein species, the microtubule gliding velocity was unaffected by the flow regardless of the flow direction or nucleotide concentration. The flow-generated force acting on a single dynein was estimated to be as small as approximately 0.03 pN/dynein. These results indicate that dynein c possesses a ratchetlike property that allows acceleration only in one direction by a very small external force. This property should be important for slow- and fast-moving dyneins to function simultaneously within the axoneme.