β-NAP, a cerebellar degeneration antigen, is a neuron-specific vesicle coat protein

We have identified a target antigen in autoimmune cerebellar degeneration, β-NAP, that is closely related to the β-adaptin and β-COP coat proteins. β-NAP is a non-clathrin-associated phosphoprotein expressed exclusively in neurons, from E12 through adulthood. β-NAP is present in the neuronal soma and nerve terminal as soluble and membrane-bound pools and is associated with a discrete set of nerve-terminal vesicles. These results establish β-NAP as a neuron-specific vesicle coat protein. We propose a model in which β-NAP mediates vesicle transport between the soma and the axon terminus and suggest that β-NAP may represent a general class of coat proteins that mediates apical transport in polarized cells.