MECHANICS OF MOTILITY - DISTINCT DYNEIN BINDING DOMAINS ON ALPHA-TUBULIN AND BETA-TUBULIN

Microtubules (MTs) interact with force-generating proteins to generate a variety of intracellular movements, including intracellular particl e transport, ciliary-flagellar beating, and chromosome-spindle movemen ts during mitosis-meiosis. Relatively little is known about the mechan ics of these motor-MT interactions, in part because the motor binding domains of the MT and the corresponding MT binding domains of the moto r have not been well characterized. Using a flagellar motility assay, we report that the MT subunits, alpha- and beta-tubulin, each contain a dynein binding domain located near the C-termini of their respective tubulin subunits. Blocking either alpha- or beta-tubulin binding doma ins of dynein attenuates motility in demembranated sea urchin sperm up to 50%. Interestingly, blocking both alpha- and beta-tubulin binding domains on dynein produces much greater decreases in motility. These d ata suggest that flagellar dynein binds to both subunits of the MT pol ymer, alpha- and beta-tubulin. In addition, the two subunits appear to contribute equivalent, but functionally separate, roles to flagellar motility.