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Three-headed outer arm dynein from Chlamydomonas that can functionally combine with outer-arm-missing axonemes.

A procedure was developed for isolating Chlamydomonas outer-arm dynein that can functionally combine with the axoneme of an outer-arm-missing mutant, oda1. Previous studies showed that the outer-arm dynein of this organism, containing three heavy chains (alpha, beta, gamma), dissociates upon extraction with a high-salt-concentration buffer solution into an 18-S particle containing the alpha and beta heavy chains and a 12-S particle containing the gamma heavy chain. It was found, however, that the three heavy chains did not dissociate if the high-salt extract was centrifuged in the presence of Mg2+; the three chains constituted a single species (23-S dynein) sedimenting at about 23 S and displayed a three-headed bouquet configuration in electron micrographs. Furthermore, the 23-S dynein had the activity to bind to the axonemes of oda1 and increase the reactivated motility of detergent-extracted cell models; its addition increased the beat frequency from 28 Hz to 53 Hz, a frequency comparable to that of wild-type axoneme. The 18-S and 12-S dyneins, on the other hand, were unable to increase the motility of oda1 axonemes even when added together. The new protocol thus enables purification of outer-arm dynein that retains its functional activity. It will provide a useful experimental system with which to study the mechanism of outer-arm function.