Kinesin superfamily protein 3 (KIF3) motor transports fodrin-associating vesicles important for neurite building

Kinesin superfamily proteins (KIFs) comprise several dozen molecular motor proteins. The KIF3 heterotrimer complex is one of the most abundantly and u biquitously expressed KIFs in mammalian cells. To unveil the functions of K IF3, microinjection of function-blocking monovalent antibodies against KIF3 into cultured superior cervical ganglion (SCG) neurons was carried out,The y significantly blocked fast axonal transport and brought about inhibition of neurite extension. A yeast two-hybrid binding assay revealed the associa tion of fodrin with the KIF3 motor through KAP3. This was further confirmed by using vesicles collected from large bundles of axons (cauda equina), fr om which membranous vesicles could be prepared in pure preparations. Both i mmunoprecipitation and immunoelectron microscopy indicated the colocalizati on of fodrin and KIF3 on the same vesicles, the results reinforcing the evi dence that the cargo of the KIF3 motor consists of fodrin-associating vesic les. In addition, pulse-labeling study implied partial comigration of both molecules as fast flow components. Taken together, the KIF3 motor is engage d in fast axonal transport that conveys membranous components important for neurite extension.