Kinesin-3 KIF1A plays prominent roles in axonal transport and synaptogenesis. KIF1A adopts a monomeric form in vitro but acts as a processive dimer in vivo. The mechanism underlying the motor dimerization is poorly understood. Here, we find that the CC1-FHA tandem of KIF1A exists as a stable dimer. The structure of CC1-FHA reveals that the linker between CC1 and FHA unexpectedly forms a β-finger hairpin, which integrates CC1 with FHA assembling a CC1-FHA homodimer. More importantly, dissociation of the CC1-FHA dimer unleashes CC1 and the β-finger, which are both essential for the motor inhibition. Thus, dimerization of the CC1-FHA tandem not only promotes the KIF1A dimer formation but also may trigger the motor activity via sequestering the CC1/β-finger region. The CC1-FHA tandem likely functions as a hub for controlling the dimerization and activation of KIF1A, which may represent a new paradigm for the kinesin regulation shared by other kinesin-3 motors.
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