The minus end depolymerase KIF2A drives flux-like treadmilling of γTuRC-uncapped microtubules

Abstract

During mitosis, a functional spindle requires high microtubule turnover. Such turnover is highlighted by the multiple functions of spindle poles, where microtubule minus ends are concentrated, and where microtubule nucleation and depolymerization happen side by side. How these seemingly antagonistic processes are coordinated during poleward microtubule flux is not understood. Here we reconstitute this coordination in vitro combining different pole localized activities. We find that the spindle pole-localized kinesin-13 KIF2A is a microtubule minus-end depolymerase, in contrast to its paralog MCAK. Due to its asymmetric activity, KIF2A still allows microtubule nucleation by plus-end growth from the {gamma}-tubulin ring complex ({gamma}TuRC), which in turn serves as a protective cap that shields the minus end against KIF2A binding. Efficient {gamma}TuRC-uncapping requires the combined action of KIF2A and a microtubule severing enzyme, then leading to treadmilling of the uncapped microtubule driven by KIF2A. Together these results provide insight into the molecular mechanisms by which a minimal protein module coordinates microtubule nucleation and depolymerization at spindle poles consistent with their role in poleward microtubule flux.