An extended microtubule-binding structure within the dynein motor domain

Flagellar dynein was discovered over 30 years ago as the first motor protein capable of generating force along microtubules(1). A cytoplasmic form of dynein has also been identified which is involved in mitosis and a wide range of other intracellular movement(2) (reviewed in ref. 3). Rapid progress has been made on understanding the mechanism of force production by kinesins and myosins(4-8). In contrast, progress in understanding the dyneins has been limited by their great size (relative molecular mass 1,000K-2,000K) and subunit complexity. We now report evidence that the entire carboxy-terminal two-thirds of the 532K force-producing heavy chain subunit is required for ATP-binding activity. We further identify a microtubule-binding domain, which, surprisingly, lies well downstream of the entire ATPase region and is predicted to form a hairpin-like stalk Direct ultrastructural analysis of a recombinant fragment confirms this model, and suggests that the mechanism for dynein force production differs substantially from that of other motor proteins.