Organization of the secretory machinery in the rodent brain: distribution of the t-SNAREs, SNAP-25 and SNAP-23

Vesicular transport events appear to be facilitated by the VAMP/synaptobrev in family of membrane proteins in the vesicle (v-SNAREs) and a heterodimeri c complex of syntaxin and SNAP-23/25 family members in the target membrane (t-SNAREs). In this manuscript we examine the tissue distribution and compo sition of the heterodimeric t-SNARE complexes in adult rodent brain. Analys is of protein extracts from brain regions shows that SNAP-25, syntaxin 1, a nd 4 are broadly distributed, while SNAP-23, syntaxin 3, and 7 show distinc t patterns of expression. Further immunohistochemistry and fractionation st udies show that while SNAP-25 is enriched in axons and nerve terminals, SNA P-23 is concentrated in cell bodies. Both SNAP-23 and SNAP-25 associate wit h the plasma membrane and can be metabolically labeled with [H-3] palmitate in AtT-20 cells. Anti-SNAP-25 antibodies co-immunoprecipitate t-SNARE hete rodimers from brain extracts that predominantly contain syntaxin 1 and 2. C ontrary to results from in vitro binding assays, SNAP-23 was found predomin antly associated with syntaxin 3. These observations suggest that t-SNARE, heterodimer composition is governed more by SNARE expression and localizati on than by simple protein-protein affinity. (C) 1999 Elsevier Science B.V. All rights reserved.