Presynaptic PKC substrate B-50 (GAP-43) and neurotransmitter release: studies with permeated synaptosomes

Protein B-50 (also known as GAP-43, pp46, neuromodulin and Fl) is a nervous tissue specific protein, which is highly expressed in neurons during development and nerve regeneration, and has been implicated in neurite outgrowth, long-term potentiation, signal transduction and neurotransmitter release. In mature neurons B-50 is expressed in most (if not all) neurons. It is predominantly found in presynaptic membranes and not in dendrites. Our antibody interference experiments show that the N-terminus of B-50 is important for release. The N-terminal domain of B-50 contains the membrane targeting signal, the CaM binding domain and the PKC phosphorylation site. Because most of the B-50 in synaptosomes is membrane attached, it is unlikely that the antibodies affect membrane attachment. In conclusion, using monoclonal anti-B-50 IgGs we established a causal relationship between B-50 and Ca(2+)-induced NA and CCK-8 release. Although a function of the C-terminal B-50 domain 132-226 cannot be excluded, we demonstrated that the N-terminus of B-50 plays an important role in the mechanism of Ca(2+)-induced NA and CCK-8 release.