Is the dynein motor a winch?

Dyneins are the largest and most complex of the three classes of linear motor proteins in eukaryotic cells. The mass of the dynein motor domain is about ten times that of the other microtubule motor, kinesin. Dynein's homology with the AAA+ superfamily of mechanoenzymes distinguishes it from both kinesin and myosin, which share a common fold and ancestry as members of the G-protein superfamily. In contrast to the other motor proteins, little is known about the mechanism of dynein; its three-dimensional structure is unknown even at low resolution. Recent two-dimensional images from electron microscopy have revealed new details of its structure and how this changes to produce movement. These and the recently solved crystal structure of another AAA+ protein, ClpB, offer tantalising hints about dynein's mechanism, suggesting it may act like a molecular winch.