Evolutionary conservation of synaptosome-associated protein 25 kDa (SNAP-25) shown by Drosophila and Torpedo cDNA clones.

The neuron-specific proteins SNAP-25 (synaptosome-associated protein 25 kDa), synaptobrevin and syntaxin, are localized to presynaptic terminals in mammals and have been found to associate with proteins involved in vesicle docking and membrane fusion. We describe here SNAP-25 cDNA clones from the fruit fly Drosophila melanogaster and the ray Torpedo marmorata. In situ hybridization showed that SNAP-25 mRNA is exclusively found in brain and ganglia in Drosophila with a pattern suggesting expression in most neurons. The Drosophila and Torpedo proteins show 61 and 81% amino acid identity to mouse SNAP-25, a degree of conservation similar to that previously reported for synaptobrevin. None of the SNAP-25 sequences has a membrane-spanning region, but all contain a cluster of cysteine residues that can be palmitoylated for membrane attachment. SNAP-25 displays sequence similarity to syntaxin A and B. These data show that SNAP-25 and synaptobrevin, which are both implicated in vesicle docking and/or membrane fusion, have both been highly conserved during evolution. This supports the existence of a basic molecular machinery for synaptic vesicle docking in vertebrate and invertebrate synapses.