Domain organization & conformational changes
Many members of the kinesin family contain an extended region of predicted alpha-helical coiled coil in the main chain that likely causes the protein to dimerize. The native complexes of several kinesin family members have also been shown to contain additional peptides, often designated light chains - as all of the noncatalytic subunits that are currently known are smaller than the chain that contains the motor unit. Kinesin-1 is an alpha2-beta2 
heterotetramer of two heavy and two light chains, whereas the Kinesin-5 (formerly BimC) subfamily proteins are homotetrameric and heterotimeric Kinesin-2 (formerly 85/95 or kinesin II) species are also known. Motor proteins share two essential functional components in a motor domain and a cargo binding domain, and most also contain a central linking domain that can be quite extended.
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
Recent reviews
- Hackney, D. D. (1996) Annu. Rev. Physiol. 58, 732-750
- Hackney, D. D. (1995) Nature 376, 215-216
- Cole, D. G. and Scholey, J. M. (1995) Trends Cell Biol. 5, 259-262
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Created 7 July 1996 20:00 GMT
Modified 25 January 2005 7:50 GMT