Nucleotide-dependent conformations of the kinesin dimer interacting with microtubules

Kinesins are crucial to eukaryotic cells. They are a superfamily of motor proteins that use ATP hydrolysis to move along microtubules. Many of these motors are heterotetramers with two heavy and two light chains. The heavy chain has a globular motor domain that interacts with microtubules and shows a similar sequence throughout the family. Compared with myosin and dynein, kinesin provides a 'simple' model for understanding molecular motors.

Electron cryomicroscopy and three-dimensional reconstruction methods have been used to investigate microtubule-kinesin dimer complexes in different nucleotide states. Three-dimensional maps were obtained in the presence of 5'-adenylylimidodiphosphate (AMP-PNP), ADP-AIF4, ADP and apyrase. In all cases, kinesin has one attached and one free head per tubulin heterodimer. The attached heads appear very similar whereas the free heads show distinct conformations and orientations depending on their nucleotide states.

The kinesin dimer is likely to undergo considerable conformational changes during its ATP hydrolysis cycle. In all nucleotide states, the kinesin dimer attaches to a microtubule using one motor domain with the other motor domain hanging free. Only the free domain changes conformation in the presence of different nucleotides, suggesting that it, or the region linking both motor domains to the coiled coil, is the determinant of directionality. These results give some structural clues as to how kinesin moves along microtubules and we describe possible models of kinesin movement based on currently available data.