We highly purified the Chlamydomonas inner-arm
dyneins e and c, considered to be single-headed subspecies. These two
dyneins reside side-by-side along the peripheral doublet microtubules of the flagellum. Electron microscopic observations and single particle analysis showed that the head domains of these two
dyneins were similar, whereas the tail domain of
dynein e was short and bent in contrast to the straight tail 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, the apparent velocity of microtubule translocation by
dynein e was found to be slow (Vap = 1.2 ± 0.1 μm/s) and appeared independent of the surface density of the motors, whereas
dynein c was very fast (Vmax = 15.8 ± 1.5 μm/s) and highly sensitive to decreases in the surface density (Vmin = 2.2 ± 0.7 μm/s).
Dynein e was expected to be a processive motor, since the relationship between the microtubule landing rate and the surface density of
dynein e fitted well with first-power dependence. To obtain insight into the in vivo roles of
dynein e, we measured the sliding velocity of microtubules driven by a mixture of
dynein e and c at various ratios. The microtubule translocation by the fast
dynein c became even faster in the presence of the slow
dynein e, which could be explained by assuming that
dynein e does not retard motility of faster
dyneins. In flagella,
dynein e likely acts as a facilitator by holding adjacent microtubules to aid
dynein c's power
stroke.