Kinetochore-Microtubule Attachment Relies on the Disordered N-Terminal Tail Domain of Hec1

Accurate chromosome segregation is dependent upon stable attachment of kinetochores to spindle microtubules during mitosis. A long-standing question is how kinetochores maintain stable attachment to the plus ends of dynamic microtubules that are continually growing and shortening. The Ndc80 complex is essential for persistent end-on kinetochore-microtubule attachment in cells [1, 2], but how the Ndc80 complex forms functional microtubule-binding sites remains unknown. We show that the 80 amino acid N-terminal unstructured tail of Hec1 is required for generating stable kinetochore-microtubule attachments. PtK1 cells depleted of endogenous Hec1 and rescued with Hec1-GFP fusion proteins deleted of the entire N terminus or the disordered N-terminal 80 amino acid tail domain fail to generate stable kinetochore-microtubule attachments. Mutation of nine amino acids within the Hec1 tail to reduce its positive charge also abolishes stable attachment. Furthermore, the mitotic checkpoint remains functional after deletion of the N-terminal 80 amino acid tail, but not after deletion of the N-terminal 207 amino acid region containing both the tail domain and a calponin homology (CH) domain. These results demonstrate that kinetochore-microtubule binding is dependent on electrostatic interactions mediated through the disordered N-terminal 80 amino acid tail domain and mitotic-checkpoint function is dependent on the CH domain of Hec1.