Tubulin tyrosination navigates the kinesin-1 motor domain to axons

Neurons form distinctive axonal and dendritic compartments that are important for directional signaling, but the mechanisms that discriminate between axons and dendrites remain elusive. Previous studies have demonstrated that the kinesin-1 motor domain is capable of distinguishing the axon from dendrites. Here we found that the amino acid substitutions in the beta5-loop8 region transformed truncated kinesin-1 from a uni-destination (that is, the axon-specific destination) to a bi-destination (that is, axons and dendrites) state. Furthermore, tyrosinated tubulins that are abundant in somatodendrites prevent the wild-type kinesin-1 from binding to microtubules, whereas the bi-destination-type kinesin-1 does not have this inhibition. Consistently, inhibition of tubulin tyrosination in rat hippocampal neurons resulted in the distribution of truncated kinesin-1 in both axons and dendrites. Our study identifies a molecular mechanism that discriminates the axonal microtubules from somatodendritic microtubules, as well as a previously unknown linkage between tubulin modification and polarized trafficking in neurons.