Visualizing a New Binding Site of ncd-Motor Domain on Tubulin

Ncd is a microtubule minus-end directed motor of the kinesin superfamily. Previously it has been shown that ncd and kinesin motor domains share the same major binding site on microtubules. Here we report a three-dimensional EM reconstruction of negatively stained two-dimensional Zn-induced tubulin crystal sheets (Zn-sheets) decorated with the ncd motor domain at a resolution of 16 Å. This work has revealed a second specific binding site for the ncd motor domain. The motor binding site on the tubulin Zn-sheets spans both α and β tubulin subunits. This binding site is located at a position different from the previously identified ncd binding site on microtubules and may play a role in motor function.