Dynein shifts into second gear
- Division of Molecular Medicine, Wadsworth Center, Albany, NY 12201; and Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, NY 12201
Although dynein, a microtubule-based molecular motor, has a respectable 40-plus-year research history, only recently has it begun to yield the innermost secrets of how it operates. Current efforts address how the bulky motor domains coordinate their activity to make processive steps along a cytoplasmic microtubule (1–3), suggest that the motor can vary its step size (4), and even demonstrate that dynein can run backward (5). The article by Shima et al. (6) in this issue of PNAS reveals another exceptional property of dynein, namely that the motor has more than one mode of force production. Such a discovery reinforces the view that dynein is more than a simple motor, perhaps indicating that further surprises are yet to come.
Dynein Is Structurally Different from Kinesin or Myosin
Dynein, myosin, and kinesin constitute the three major families of cytoskeleton-based motor proteins that operate in eukaryotic cells (7, 8). The exceptionally large mass (1–2 million Da as a stand-alone macromolecular complex) has long distinguished dynein from the other two families of motors. For both the native molecules and their motor domains, dynein is approximately four times larger than the actin-based myosin II. This size difference is more dramatic when dynein is compared with the other microtubule-based motor family, kinesin. The minimal mass required for complete dynein motor activity is ≈300–400 kDa, whereas kinesin fragments as small as 35–40 kDa support microtubule movement. Yet, despite this size difference, both microtubule-based motors do approximately the same thing. Both move along a microtubule at rates in the range of 0.5–2 μm/s, and both …
*E-mail: koonce{at}wadsworth.org
