Search for new biological motors

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This research was aimed at elucidating the characteristic functional properties of various biological motor proteins, focusing on axonemal dyneins and plant myosins. Axonemal dyneins, the motor proteins that produce ciliary and flagellar beating, exist as 11 different species arranged along the outer doublet microtubules. Despite extensive studies, their functional characteristics have not been established. In the present study, Chlamydomonas mutants lacking specific species of inner arm dynein were isolated, yielding important clues as to the function and localization of inner-arm dynein subspecies. In addition, through analyses of proteins interacting with various dyneins, a new protein complex was found that anchor dyneins to the microtubule. Finally, force production by a single dynein molecule was measured in vitro, in the first single-molecule measurement on dynein. A new feature of dynein force production was discovered ; dynein changes its force production properties depending on the concentration of ATP. Plant myosin studies identified two new kinds of myosins in cultured tobacco cells. One was found to bind calmodulin. Interestingly, this myosin decreased its motile activity at increased calcium concentrations ; this is one of the first examples that clearly show an inhibitory effect of calcium ion on plant myosin. Also, the gene of Chara (an alga) myosin, a motor protein known to produce an extremely rapid movement, was cloned and the protein was successfully expressed in cultured cells as well as in cellular slime mold. An unexpected finding was that a chimeric construct, with the head motor domain derived from Chara and the tail region from slime mold, displayed much slower speed than native Chara myosin. Therefore, the reason why Chara myosin produces very rapid movement has remained a puzzle.