TinA enables kinesin-14/KlpA to exhibit processive minus-end-directed motility

Kinesin-14 motors contribute to spindle assembly by localizing to spindle poles and anchoring the minus ends of spindle microtubules. Unlike other kinesin-14 motors, KlpA uniquely exhibits plus-end-directed motility on single microtubules as individual homodimers. However, the mechanism by which KlpA achieves minus-end-directed motility on single microtubules remains elusive. Here, we report that TinA, a highly conserved microtubule-anchoring protein, serves as an activator of KlpA for minus-end-directed motility. TinA directly interacts with KlpA to form minus-end-directed complexes that exhibit continuous movement on microtubules with two distinct velocity modes. The assembly of KlpA-TinA complexes depends on TinA binding to the central stalk of KlpA. Furthermore, TinA is a microtubule-binding protein, with its C-terminal region playing a critical role in microtubule interaction. Deletion of the C-terminus of TinA markedly reduces its microtubule-binding ability and severely impairs the formation of KlpA-TinA complexes. Nonetheless, KlpA-TinA complexes formed without the C-terminus of TinA still exhibit minus-end-directed motility, albeit with a single velocity mode. Collectively, these findings provide critical mechanistic insights into how TinA modulates KlpA, enabling the kinesin-14 motor to achieve minus-end-directed motility.