Cytoplasmic dynein functions as a gear in response to load


Cytoskeletal molecular motors belonging to the kinesin and dynein families transport cargos (for example, messenger RNA, endosomes, virus) on polymerized linear structures called microtubules in the cell1. These ‘nanomachines’ use energy obtained from ATP hydrolysis to generate force2, and move in a step-like manner on microtubules. Dynein3,4,5 has a complex and fundamentally different structure from other motor families. Thus, understanding dynein's force generation can yield new insight into the architecture and function of nanomachines. Here, we use an optical trap6 to quantify motion of polystyrene beads driven along microtubules by single cytoplasmic dynein motors. Under no load, dynein moves predominantly with a mixture of 24-nm and 32-nm steps. When moving against load applied by an optical trap, dynein can decrease step size to 8 nm and produce force up to 1.1 pN. This correlation between step size and force production is consistent with a molecular gear mechanism. The ability to take smaller but more powerful strokes under load—that is, to shift gears—depends on the availability of ATP. We propose a model whereby the gear is downshifted through load-induced binding of ATP at secondary sites in the dynein head.

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Figure 1: Stall force of cytoplasmic dynein.
Figure 2: Dynein takes shorter steps under load.
Figure 3: Cytoplasmic dynein takes predominantly 24- and 32-nm steps under no load.
Figure 4: Model for an ATP-regulated gear.


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R.M. acknowledges a postdoctoral fellowship from the International Human Frontier Science Program Organization. B.C.C. acknowledges support from an NIH training grant. This work was supported by a NIGMS and a CRCC grant (to S.P.G.).

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Correspondence to Steven P. Gross.

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Mallik, R., Carter, B., Lex, S. et al. Cytoplasmic dynein functions as a gear in response to load. Nature 427, 649–652 (2004).

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