Slow Dynein E with No Retardation Effects: Implication of Indirect Cooperation with Fast Dynein C

We highly purified the Chlamydomonas inner-arm dynein “e” and “c,” which reside in a pairwise fashion along the peripheral doublet microtubules. Electron microscopic observations and single particle analysis showed that the head domains of these two dyneins were similar while the tail domain of dynein e was short and bent in contrast to that of dynein c. The ATPase activities, both basal and microtubule-stimulated, of dynein e (kcat = 0.27 s−1 and kcat,MT = 1.09 s−1, respectively) were lower than those of dynein c (kcat = 1.75 s−1 and kcat,MT = 2.03 s−1, respectively). From in vitro motility assays, microtubule translocation by dynein e was found to be slow (V = 1.2 ± 0.1 µm/s) and appeared independent of the surface density, whereas that by dynein c was very fast (Vmax = 15.8 ± 1.5 µm/s) and highly sensitive to the decrease in the surface density (Vmin = 2.2 ± 0.7 µm/s). Dynein e was expected to be a processive motor, judged from the microtubule landing assay. To obtain insight into the in vivo roles of dynein e, we measured the sliding velocity of microtubules driven by a mixture of dyneins e and c of various ratios. The microtubule translocation by the “fast” dynein c became even faster in the presence of the “slow” dynein e, suggesting that dynein e would not retard the microtubule translocation by a fast dynein. In flagella, dynein e may hold adjacent microtubules for the sake of dynein c's power stroke. Moreover, dynein e may be recruited into the flagellar motion when the local velocity of microtubule sliding is not high.