Make room for dynein.

Three classes of cytoskeletal motor protein have been identified--myosins, kinesins and dyneins. Together, these proteins are now thought to be responsible for the remarkable variety of movements that occur in eukaryotic cells and that are essential for reproduction and survival. Crystallographic analysis of the myosin and kinesin motor domains at atomic resolution has provided insight into their mechanism of force production. However, because of its relative intractability to molecular manipulation, definition of the dynein motor domain, let alone progress in understanding how it works, has been slower. Evidence now indicates that the microtubule-binding domain of dynein is spatially isolated from the ATPase domain at the tip of a projecting coiled coil. As proposed here, this curious arrangement might serve to accommodate multiple copies of the outsized and functionally complex motor heads on the microtubule surface.