Kinesin-13 proteins are a group of motors that are not motile on microtubules, but instead catalyze the ATP-dependent depolymerization of microtubules in vivo and in vitro. Their functions are important for accurate chromosome segregation in mitosis. Our goal is to elucidate the structural basis of the mechanism-of-action of these motors by studying the interaction of kinesin-13s with microtubules.Previously we have shown that the kinesin-13 motor domain (MD) in ATP-bound state has the unusual property to form rings/spirals around microtubules. We have recently obtained a medium resolution three-dimensional (3D) density map of the kinesin13-ring-microtubule complex by cryo-electron microscopy and image analysis. An atomic model of the complex has been built by docking the crystal structures of tubulin and a kinesin13 MD into the 3D map. Our model reveals a snapshot of the depolymerization mechanism by providing a 3D view of the complex formed between the kinesin13 MDs and a curved tubulin protofilament. It suggests that contacts mediated by kinesin13 class-specific residues in the putative microtubule-binding site stabilize intra-dimer tubulin curvature. In addition, a new tubulin-binding site on the kinesin13 MD was identified. Mutations at this class-conserved site selectively disrupt the formation of microtubule-associated ring complexes.