The Crystal Structure of Dimeric Kinesin and Implications for Microtubule-Dependent Motility

Abstract

The dimeric form of the kinesin motor and neck domain from rat brain with bound ADP has been solved by X-ray crystallography. The two heads of the dimer are connected via a coiled-coil alpha-helical interaction of their necks. They are broadly similar to one another; differences are most apparent in the head-neck junction and in a moderate reorientation of the neck helices in order to adopt to the coiled-coil conformation. The heads show a rotational symmetry (approximately 120 degrees) about an axis close to that of the coiled-coil. This arrangement is unexpected since it is not compatible with the microtubule lattice. In this arrangement, the two heads of a kinesin dimer could not have equivalent interactions with microtubules.

Congruent Docking of Dimeric Kinesin and ncd into Three-dimensional Electron Cryomicroscopy Maps of Microtubule–Motor ADP Complexes

“…A volume of protein density above the left one-half of the bound head that remains unfilled (Figure 6c) is essentially where the tethered head should be positioned to agree with the dimeric kinesin crystal structure (Kozielski et al, 1997), with the attached head corresponding to head B. Although the map has insufficient density at high radius to accommodate all of head A, probably because of disorder, a second copy of the monomer crystal structure (Figure 6, pink), in an orientation close to that of head A in the crystal structure, readily accounted for the extra density.…”

“…Monomeric and dimeric (Kozielski et al, 1997) rat kinesin constructs revealed two additional ␤ strands (␤9 and ␤10) at the C terminus, which are thought to be important for determining the directionality, and an ␣ helix (␣7) that forms a coiled coil in the dimer structure. In crystals of dimeric kinesin two motor domains are asymmetrically related to each other by an ϳ120°rotation.…”

“…On the other hand, attempts to relate the crystal structures of dimeric kinesin (Kozielski et al, 1997;Hoenger et al, 1998) to complexes seen by electron microscopy have been unsatisfactory. When one of the heads ("head B" in the crystal structure) of dimeric kinesin is docked in the orientation chosen by Sosa et al (1997) and Hoenger et al (1998), the coiled coil that dimerizes the two heads points into the microtubule surface.…”

Microtubule shuttles on kinesin-coated glass micro-wire tracks

“…Assuming that all kinesin molecules in solution within the flow cell attach to the glass surfaces, the kinesin surface density from the 4 µM kinesin solution is estimated to be 108,000 molecules per 1 µm 2 . This is well beyond the saturation limit determined by the size of a single kinesin motor head because it corresponds to one kinesin molecule in an area of ~3 nm × 3 nm which is smaller than the size of a kinesin motor head (~8 nm in diameter) (Kozielski et al, 1997). In order to characterize the general aspect of the motility, we observed microtubules gliding on a region of the coverslip (area: ~50 µm × 50 µm) away from the glass wire (Supplementary Movie, SM12).…”

Kinesin motors as molecular machines

“…(41) Although the neck linker was disordered in the first crystal structure of a kinesin motor, (42) presumably due to its mobility in the crystal lattice, subsequent crystal structures show a visible neck linker consisting of two b-strands that interact with other b-strands of the motor domain. (41,43) The mobile or undocked conformation of the neck linker is thought to alternate with docking against the motor core. Undocking of the neck linker would not only potentially enable the two heads of dimeric conventional kinesin to reach between two adjacent binding sites along the microtubule, but could also amplify a small movement of the motor core, producing a power stroke.…”