Key result
The forward stepping rate of myosin VI was proportional to ATP concentration, whereas the backward stepping rate was independent (0.62 s-1), indicating backward steps occur via spontaneous detachment.
Single-molecule imaging reveals that myosin VI backward steps are caused by spontaneous detachment of the leading head, independent of ATP binding.
Hypothesis-generating for myosin VI mechanics in vitro; leaves open relevance to cardiac contractility in vivo.
Myosin VI is an ATP driven molecular motor that normally takes forward and processive steps on actin filaments, but also on occasion stochastic backward steps. While a number of models have attempted to explain the backwards steps, none offer an acceptable mechanism for their existence. We therefore performed single molecule imaging of myosin VI and calculated the stepping rates of forward and backward steps at the single molecule level. The forward stepping rate was proportional to the ATP concentration, whereas the backward stepping rate was independent. Using these data, we proposed that spontaneous detachment of the leading head is uncoupled from ATP binding and is responsible for the backward steps of myosin VI.
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Ikezaki et al. (2013) studied Myosin VI molecular motor function. ATP concentration was evaluated on Forward and backward stepping rates. The forward stepping rate of myosin VI was proportional to ATP concentration, whereas the backward stepping rate was independent (0.62 s-1), indicating backward steps occur via spontaneous detachment.
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