Abstract
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.
Highlights
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
We show that SNAP-25 is distantly related to other proteins involved in vesicle docking, namely syntaxin, Sed5p and Pepl2p
Two synapse proteinshave previously been characterized in both mammals and Drosophila, and both were found to display extensive sequence conservation; the integral synaptic vesicle proteins synaptotagmin (Perin et al, 1991) and synaptobrevin/VAMP (Sudhof etal., 1989) both display 57% overall identity between Drosophila and mammals
Summary
Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York. SNAP-25 cDNA clones have previously been isolated from chicken (Catsicas et al, 1991) and thepredicted protein was identical to themouse protein throughout the 206 amino acids (Catsicaset al., 1991).Cloning of the chicken gene (Bark, 1993) has revealed a complex exon organization with eight exons distributed over at least 65 kb.two similar but distinct variants of exon 5 were discovered in chicken as well as in mouse and human. I n Situ Hybridization-12-pm cryostat sections of unfixed Drosophila tissue were processed for in situ hybridization as previously described (Pieribone et al, 1992) usinga %labeled 48-mer DNA probe (see Fig. l ) , which is complementary to the part encoding the cysteine cluster of Drosophila SNAP-25. Sections were counterstained withtoluidin blue (head sections) or cresyl violet (body sections)
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