Translocations of fodrin and its binding proteins

Fodrin, a protein related to erythrocyte spectrin, redistributes within the cell in certain situations. We compare such movements of fodrin and several fodrin binding proteins during the processes of axonal transport in neurons, and capping of surface proteins in lymphocytes. In neurons, three different populations of newly synthesized fodrin appear to be transported down the axons at different velocities corresponding to those of groups of transported proteins designated II, IV, and V. Actin, which can interact with fodrin, is transported at the velocity of group IV. Synapsin, a component of synaptic vesicles, is also reported to bind to fodrin. One population of synapsin is transported more rapidly than fodrin, at the velocity of group I: two additional populations of transported synapsin may overlap fodrin in groups II and IV. We consider possible functional associations of these different populations of fodrin and fodrin binding proteins. We note that the transport of group IV proteins resembles in certain respects the process of capping in lymphocytes, suggesting the possibility of a common mechanism. We outline one of several possible mechanisms.