Molecular Motors


(Click on figures to enlarge and view figure legends)
Vale worked together with Mike Sheetz, Bruce Schnapp and Tom Reese on the mechanism of axonal transport, which led to the development of in vitro motility assays for microtubule-based motility and the discovery of kinesin.  With Joe Howard/Jim Hudspeth and Toshio Yanagida, these assays for refined to probe kinesin motility at a single molecule level.  Together with Robert Fletterick's laboratory at University of California, San Francisco, we determined the atomic resolution structure of the kinesin motor domain and discovered unexpectedly that it is similar in structure to myosin, an actin-based motor. This was an important finding this it allowed us to compare kinesin and myosin (and also G proteins, which are also evolutionarily related) and identify common structural features that might reflect conserved aspects of the motor mechanism.


Using a combination of single-molecule spectroscopy, cryoelectron microscopy (with Ron Milligan's group, Scripps Research Institute), pre-steady-state kinetics (with Ed Taylor), and mutagenesis techniques, we identified a critical mechanical element in kinesin (called the neck linker) and showed that it undergoes nucleotide- and microtubule-dependent conformational changes. This allowed us to construct a structural model that explains the known features of kinesin movement.  This model and comparison with myosin is featured in a review article in 2000 (Vale and Milligan, Science 2000), which still reflects a reasonably good contemporary description of these molecular machines.  The neck linker docking model was later supported by mutagenesis studies (Case et al., 2000), crosslinking experiments (Tomishige and Vale, 2000), demonstration of hand-over-hand motion of kinesin’s two heads (Yildiz et al., 2004), single molecule FRET expeiments (Tomishige et al., 2006), and optical trapping experiments (Yildiz et al., 2008).


The animations of the motility cycle of kinesin and myosin shown below (prepared by Graham Johnson) were from this review. The key features of the kinesin model in this animation from the Science review are as follows. Kinesin is a dimeric motor protein that travels processively towards the microtubule plus end by taking 8 nm steps (shown by Steve Block and colleagues), which corresponds to the distance between adjacent alpha/beta tubulin binding sites. The coiled coil dimerization domain is shown in grey (the attached cargo would be at the end of the coiled coil, which is much longer than shown here). The Rice et al. paper proposed that a small peptide called the neck linker docks to the catalytic core in “ATP” states and undocks in “ADP” or nucleotide-free states. (The docked state is Yellow in the movie and undocked state is Red). When the rear head detaches (after phosphate release), the neck linker docking in the front head biases the position of the detached partner head from a rear to a forward position. After a Brownian search (illustrated by the bouncing motion of the head in the animation), it docks onto the forward tubulin binding site and this interaction causes ADP to be released. This microtubule binding event completes the 8 nm step and generates force. This cycle can then repeat as the kinesin takes many steps along the microtubule and the rear head can pass on either side of front head so as not to build up twist in the coiled coil. Normally, the “step” (rearward detachment, translation past the partner head, diffusional search, and docking) would occur extremely rapidly and occupy a very small fraction of the ATPase cycle (see also studies by Carter and Cross).


Animated Movies


Left: Animated model of processive motion by conventional kinesin. Right: Animated model for myosin based motililty. These animations were prepared by Graham Johnson ( and are based upon atomic structures representing different nucleotide states (Vale and Milligan, 2000).

Many questions remain, such as whether kinesin waits in between steps as a two-head bound intermediate (as shown in this movie) or as a one-head-bound intermediate.  We have suggested a two-head-intermediate at high ATP and a one-head-bound at very low (non-physiological) ATP (Mori et al., 2008).  However, a general one-head-bound waiting state has been favored by other investigators. The mechanism of how the two kinesin motor domains communicate so that their ATPase cycles remain coordinated and out of phase also remains unsettled and a very active topic of investigation in the field (see also our recent work by Yildiz et al, 2008). More detailed information on how kinesin interacts with microtubules also is needed.  These are all questions that remain of interest to our laboratory.


We also have been interested in studying the mechanism of other members of the kinesin family.  With Fletterick, we obtained the crystal structure for the minus-end-directed Kinesin 14 motors (e.g. Ncd)(Sablin et al., 1996, 1998) and with Milligan found that Ncd has a very different mechanical element than the kinesin neck linker and that this mechanical element undergoes a minus-end-directed rigid power stroke (more analogous to myosin (Endres et al., 2006). More recently, with Gohta Goshima (Nagoya University) we are examining the biophysical properties of the kinesin 14 family (minus-end-directed motors) in plants.



Of additional interest is the Kinesin-3 family. We reported that this group of kinesins might undergo a regulated monomer to dimer transition to produce a fully processive motor (Tomishige et al., 2002; Klopfenstein et al., 2002). More recently, we studied kinesin-73, another member of this class of kinesins, which has a similar monomer-dimer equilibrium in vitro but might be dimerized in the cell (Huckaba et al., 2011).

In addition, we have been interested in understanding how kinesin motility is regulated.  Both conventional kinesin (kinesin 1) and Osm-3 (an kinesin 2) shut off processive motility through a fold-back, autoinihibited state between the distal tail and motor domains (Friedman and Vale, 1999; Imanishi et al., 2006).  With Ron Milligan, we also found that Unc104 (a kinesin 3) may have an autoinhibited state in its neck coiled-coil region that inhibits its dimerization (Al-Bassam et al., 2003).



See additional movies and images here.

See also web sites of former lab members who are continuing to study kinesin motors:


A selection of our lab's publications on kinesin:

  • (pdf) - Huckaba, T.M., Gennerich, A., Wilhelm, J.E., Chishti, A.H. and Vale, R.D. (2011) Kinesin-73 is a processive motor that localizes to Rab5-containing organelles. J Biol Chem 286: 7457-7467.
  • (pdf) - Yildiz, A., Tomishige, M., Gennerich, A., Vale, R.D. (2008) Intramolecular strain coordinates kinesin stepping behavior along microtubules. Cell 134: 1030-1041.
  • (pdf) - Mori, T., Vale, R.D. and Tomishige, M. (2007) How kinesin waits between steps. Nature 450: 750-755.
  • (pdf) - Imanishi, M., Endres, N.F., Gennerich, A., and R.D. Vale (2006) Autoinhibition regulates the motility of the C-elegans intraflagellar transport motor OSM-3. J Cell Biol 174: 931-937.
  • (pdf) - Endres, N.F., Yoshioka, C., Milligan, R.A. and R. D. Vale. (2006) A lever arm rotation drives motility of the minus-end-directed kinesin, Ncd. Nature 439: 875-878.
  • (pdf) - Tomishige, M., Stuurman, N., and Vale, R.D. (2006) Single-molecule observations of neck linker conformational changes in the kinesin motor protein. Nat. Struct. Molec. Biol. 13: 887-894.
  • (pdf) - Yildiz, A., Tomishige, M., Vale, R.D. and Selvin, P.R. (2004) Kinesin walks hand-over-hand. Science 303: 676-678.
  • (pdf) - Al-Bassam, J., Cui, Y., Klopfenstein, D., Carragher, B.O., Vale, R.D. and Milligan, R. A. (2003) Distinct conformations of the kinesin Unc104 neck regulate a monomer-to-dimer motor transition. J Cell Biol 163: 743-753.
  • (pdf) - Rice, S., Cui, Y., Sindelar, C., Naber, N., Matuska M., Vale, R. and Cooke R. (2003) Thermodynamic properties of the kinesin neck region docking to the catalytic core. Biophysical J 84:1844-1854.
  • (pdf) - Klopfenstein, D., Tomishige, M., Stuurman, N. and Vale, R.D. (2002) Role of Phosphatidylinositol(4,5)bisphosphate Organization in Membrane Transport by the Unc104 Kinesin Motor. Cell 109: 347-358.
  • (pdf) - Tomishige, M., Klopfenstein, D., and Vale, R.D. (2002) Conversion of Unc104/KIF1A kinesin into a processive motor after dimerization. Science 297: 2263-2267.
  • (pdf) - Case, R. B., Rice, S., Hart, C., Ly, B., and Vale, R.D. (2000) Role of the kinesin neck linker and catalytic core in microtubule-based motility. Curr Biol 10: 157- 160.
  • (pdf) - Thorn, K.S., Ubersax, J.A., and Vale, R.D. (2000) Engineering the processive run length of the kinesin motor. J Cell Biol 151: 1093-1100.
  • (pdf) - Tomishige, M. and Vale, R.D. (2000) Controlling kinesin by reversible disulfide cross-linking: identifying the motility-producing conformational change. J Cell Biol 151: 1081-1092.
  • (pdf) - Vale, R.D., Milligan, R.A. (2000) The way things move: looking under the hood of molecular motor proteins. Science 288: 88-95.
  • (pdf) - Friedman, D. S. and Vale, R. D. (1999) Single molecule analysis of kinesin motility reveals regulation by the cargo-binding tail domain. Nature Cell Biol. 1: 293-297.
  • (pdf) - Rice, S., Lin, A., W., Safer, D., Hart, C. L., Naber, N., Carragher, B. O., Cain, S. M., Pechatnikova, E., Wilson-Kubelek, E. M., Whitaker, M., Pate, E., Cooke R. , Taylor, E. W., Milligan, R. A., and Vale, R. D. (1999) A structural change in the kinesin motor protein that drives motility. Nature 402: 778-783.
  • (pdf) - Romberg, Laura, Pierce, Daniel W., and Vale, Ronald D. (1998) Role of the kinesin neck region in processive microtubule-based motility. J Cell Biol 140: 1407-1416.
  • (pdf) - Sablin E.P., Case R.B., Dai S.C., Hart C.L., Ruby A., Vale R.D. and Fletterick, R. (1998) Direction determination in the minus-end-directed kinesin motor ncd. Nature 395: 813-816.
  • (pdf) - Case, Ryan B., Pierce, Daniel W., Hom-Booher, Nora, Hart, Cynthia L. and Vale, Ronald D. (1997) The directional preference of kinesin motors is specified by an element outside of the motor catalytic domain. Cell 90: 959-966.
  • (pdf) - Sosa, Hernando, Dias, D. Prabha, Hoenger, Andreas, Whittaker, Michael, Wilson-Kubalek, Elizabeth, Sablin, Elena, Fletterick, R., Vale, Ronald D and Milligan, Ronald A. (1997) A model for the microtubule-Ncd motor protein complex obtained by cryo-electron microscopy and image analysis. Cell 90: 217-224.
  • (pdf) - Woehlke, Günther, Ruby, Aaron K., Hart, Cynthia L., Ly, Bernice, Hom-Booher, Nora and Vale, Ronald D. (1997) Microtubule interaction site of the kinesin motor. Cell 90: 207-216.
  • (pdf) - Vale, Ronald D. and Fletterick, R. (1997) The design plan of kinesin motors. Annu Rev Cell Dev Biol 13: 745-77.
  • (pdf) - Kull, F. Jon, Sablin, Elena P., Lau, Rebecca, Fletterick, R. and Vale, Ronald D. (1996) Crystal structure of the kinesin motor domain reveals a structural similarity to myosin. Nature 380: 550-555.
  • (pdf) - Sablin, Elena P., Kull, F. Jon, Cooke R., Vale, Ronald D. and Fletterick, R. (1996) Crystal structure of the motor domain of the kinesin-related motor ncd. Nature 380: 555-559.
  • (pdf) - Vale, Ronald D. (1996) Switches, latches and amplifiers: common themes of G proteins and molecular motors (Commentary). J Cell Biol 135: 291-302.
  • (pdf) - Vale, Ronald D., Funatsu, Takashi, Pierce, Daniel W., Romberg, Laura, Harada, Yoshie and Yanagida, Toshio. (1996) Direct observation of single kinesin molecules moving along microtubules. Nature 380: 451-453.
  • (pdf) - Hoenger, A., Sablin, E.P., Vale, R.D., Fletterick, R., and Milligan, R.A. (1995) Three-dimensional structure of a tubulin-motor protein complex. Nature 376: 271-274.
  • (pdf) - Romberg, L. and Vale, R.D. (1993) Chemomechanical cycle of kinesin differs from that of myosin. Nature 361: 168-170.
  • (pdf) - Howard, J., Hudspeth, A.J. and Vale, R.D. (1989) Movement of microtubules by single kinesin molecules. Nature 342: 154-158.
  • (pdf) - Schnapp, B.J., Vale, R.D., Sheetz, M.P. and Reese, T.S. (1985) Single microtubules from squid axoplasm support bidirectional movement of organelles. Cell 40: 455-462.
  • (pdf) - Vale, R.D., Reese, T.S. and Sheetz, M.P. (1985) Identification of a novel force generating protein, kinesin, involved in microtubule-based motility. Cell 42: 39-50. (pdf) - Vale, R.D., Schnapp, B.J., Mitchison, T., Steuer, E., Reese, T.S. and Sheetz, M.P. (1985) Different axoplasmic proteins generate movement in opposite directions along microtubules in vitro. Cell 43: 623-632.
  • (pdf) - Vale, R.D., Schnapp, B.J., Reese, T.S. and Sheetz, M.P. (1985) Organelle, bead and microtubule translocations promoted by soluble factors form the squid giant axon. Cell 40: 559-569.
  • (pdf) - Vale, R.D., Schnapp, B.J., Sheetz, M.P. and Reese, T.S. (1985) Movement of organelles along filaments dissociated from the axoplasm of the squid giant axon. Cell 40: 449-454. (cover) .


updated 5/15/2012