SNAP-25.

SNAP-25 belongs to a family of evolutionarily conserved proteins whose members are essential for exocytosis. Neurons and neuroendocrine cells differentially express two SNAP-25 isoforms in a developmentally regulated manner, and related homologues have been detected in most eukaryotic cells. SNAP-25 is localised on the cytoplasmic face of the plasma membrane and on secretory vesicles. It forms a stable ternary complex with two other exocytotic proteins: syntaxin and the synaptic vesicle protein synaptobrevin. A cytosolic ATPase dissociates this complex during priming of the exocytotic apparatus. Subsequent reassembly is promoted by SNAP-25 and may drive Ca(2+)-triggered vesicle-plasma membrane fusion. A mutant mouse that lacks the SNAP-25 gene is defective in neuronal dopamine signalling and exhibits similar behaviour as sufferers from hyperactivity disorders. Use of this animal model thus provides a promising avenue for the development of therapeutic treatments. Additionally, SNAP-25-based peptides that mimic the effect of botulinum neurotoxin A may be used for the treatment of involuntary muscle spasms.