Neurotransmitter release is dependent on a binding complex (designated as SNAR) of three proteins, synaptic-vesicle-associated protein synaptobrevin/VAMP, syntaxin and SNAP-25 (snaptosome-associated protein-25) with results in a calcium dependent fusion between synaptic vesicles and the presynaptic terminal. SNAPIN, a neuron specific protein found predominately on synaptic vesicles, binds to the SNAR complex, most likely to the SNAP-25. Although the complete function of SNAPIN has not been determined, it appears to regulate a step between vesicle docketing and neurotransmitter release through its ability to potentiate the interaction of synaptotagmin with the SNAREs, which then leads to the final fusion step triggered by calcium influx into nerve terminals through voltage-dependent calcium channels.