Cytoplasmic dynein functions as a gear in response to load

Abstract

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 cell. These 'nanomachines' use energy obtained from ATP hydrolysis to generate force, and move in a step-like manner on microtubules. Dynein 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 trap 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.

Intracellular transport driven by cytoskeletal motors: General mechanisms and defects

“…In [242], it was reported that under no load, dyneins were taking predominantly 24-and 32-nm long steps, and that the step length was decreasing under load. Later, more direct measurements of dynein displacement were performed through high temporal resolution fluorescence.…”

Molecular motors: not quite like clockwork

“…The centre of the head would appear to move an even shorter distance; 3.7nm has been measured for axonemal dynein [48]. However, if the dynein stalk were to flex towards the minus end while first making an attachment (conformation shown dotted in step 6) instead of pointing at 90° to the MT, the cargo could subsequently be moved by 16nm; 24nm shifts also reported during movement under low loads [59] could possibly be produced by simultaneously flexing the bound stalk in the other direction (conformation shown by dotted line in step 3).…”

A modified active Brownian dynamics model using asymmetric energy conversion and its application to the molecular motor system

“…Since the stepping motion of kinesin was first observed by a single-molecule experiment [1], similar discrete motions of various molecular motors have been reported [2][3][4][5]. Singlemolecule techniques [6,7] have shed light on the mechanisms of these tiny biological motors.…”