Kinesin-1 is in an unfolded conformation with a sedimentation coefficient of 6 S at high ionic strength, but folds into a compact 9 S conformation at low ionic strength as indicated in the figure. The folding is driven by interaction between a region in the head and a region in the tail of the heavy chain, as the homodimer of only heavy chains also shifts between an unfolded 5 S and a folded 7 S conformation in the absence of light chains. Analysis of microtubule-stimulated ATPase activity indicates that the folded form is inhibited and does not have the maximal velocity or high affinity for microtubules that are required for generation of processive motion. Dimers of isolated head domains possess the required ATPase properties and likely operate in a head-over-head mechanism.
Electron microscopy of head domains bound to microtubules indicates that the orientation of Kinesin-1 and Ncd (Kinesin-14) heads are similar in spite of their different directions of movement. In addition, part of the Kinesin-1 head domain appears to swing in a nucleotide-dependent manner that may be related to the power stoke for generation of movement.
Contributed by David Hackney
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