The mitotic spindle is a macromolecular structure utilized to properly align and segregate sister chromatids to two daughter cells. During mitosis, the spindle maintains a constant length, even though the spindle microtubules (MTs) are constantly undergoing polymerization and depolymerization . Members of the kinesin-8 family are important for the regulation of spindle length and for chromosome positioning [2-9]. Kinesin-8 proteins are length-specific, plus-end-directed motors that are proposed to be either MT depolymerases [3, 4, 8, 10, 11] or MT capping proteins . How Kif18A uses its destabilization activity to control spindle morphology is not known. We found that Kif18A controls spindle length independently of its role in chromosome positioning. The ability of Kif18A to control spindle length is mediated by an ATP-independent MT binding site at the C-terminal end of the Kif18A tail that has a strong affinity for MTs in vitro and in cells. We used computational modeling to ask how modulating the motility or binding properties of Kif18A would affect its activity. Our modeling predicts that both fast motility and a low off rate from the MT end are important for Kif18A function. In addition, our studies provide new insight into how depolymerizing and capping enzymes can lead to MT destabilization.
Bibliographical noteFunding Information:
This work was supported by National Institutes of Health grant R01-GM059618 to C.E.W.; an American Society for Cell Biology Scholarship, Center for Modular Biology Fellows Scholarship, and William Townsend Porter Scholarship to L.N.W.; National Science Foundation grant MCB-0920555 to S.L.S.; and a Whitaker International Scholar Award to M.K.G. The authors are especially grateful to David Odde, Clare Waterman, Dyche Mullins, and Wallace Marshall for assistance and inspiration in formulating aspects of this project at the Marine Biology Laboratory. Yvonne Brede, Romy Brauer, Jennifer Rawlinson, and Brandon Hill provided assistance for early work on the project.