VAMP/synaptobrevin

Synaptobrevins (VAMPs) Synaptogyrin Synaptophysins PKA but diverge C-terminally. Synapsins Ia/b contain C-terminal phosphorylation sites for CaMKII and CDK 5. Interact with microfilaments, neurofilaments, microtubules, SH3 domains, calmodulin and annexin VI in vitro. Small-membrane proteins that are cleaved by tetanus toxin and by botulinum toxins B, D, F and G. Polytopic membrane protein that is tyrosine-phosphorylated. Function unknown. Polytopic membrane proteins, including synaptoporin, that are tyrosine-phosphorylated and bind to synaptobrevins. May regulate SNARE function... 

Synaptobrevins (VAMPs)b Synaptophysins, synaptogyrin SV2 A, B, C SCAMPS 1 and 4 SVOP... 

Synaptic exocytosis involves three SNARE proteins the R-SNARE synaptobrevin/VAMP (isoforms 1 and 2) on the vesicle, and the Q-SNAREs syntaxin (isoforms 1 and 2) and SNAP-25 on the plasma membrane (Figure 4). Since SNAP-25 has two SNARE-motifs, synaptobrevin, syntaxin, and SNAP-25 together have four SNARE-motifs. Synaptobrevins and SNAP-25 are relatively simple SNARE proteins that are composed of little else besides SNARE motifs and membrane-attachment sequences (a transmembrane region for synaptobrevin, and a cysteine-rich palmitoylated sequence for SNAP-25). Syntaxins, in contrast, are complex proteins. The N-terminal two-thirds of syntaxins include a separate, autonomously folded domain (the so-called Habc-domain), while the C-terminal third is composed of a SNARE motif and transmembrane region just like synaptobrevin. 

It is now well established that in vivo efficient membrane fusion requires the interaction of small cytoplasmically exposed membrane proteins called soluble N-ethylmaleimide sensitive factor (NSF) attachment receptors (SNAREs) (Sollner et al., 1993). For synaptic vesicle exocytosis, the relevant SNAREs are synaptobrevin/ vesicle-associated membrane protein (VAMP) 1 and 2, syntaxin 1, and synaptosome-associ-ated protein of 25,000 daltons (SNAP-25). Synaptobrevins/ VAMPs are localized primarily on synaptic vesicles, while syntaxin and SNAP-25 are localized primarily on the plasma membrane. Fusion is driven by the progressive zippering of vesicle and plasma membrane SNAREs forming a four-helix bundle (Sutton et al., 1998). Although many other proteins appear to play critical roles in synaptic vesicle exocytosis, it seems likely that SNAREs are the minimal machinery required for fusion (Weber et al., 1998). Once assembled, SNARE complexes are disassembled by NSF, which functions in conjunction with SNAP proteins. 

Yamasaki S, Hu Y, BinzT, Kalkuhl A, Kurazono, Tamura T, Jahn R, Kandel E, Niemann H (1994 b) Synaptobrevin/VAMP of Ap//s/o californica structure and proteolysis by tetanus and botulinal neurotoxins type D and F. In Proc. Natl. Acad. Sci. USA 91 4688-92... 

Serotypes B, D, E, and G cleave different sites on the synaptic vesicle protein, synaptobrevin (VAMP), whereas serotypes A and E cleave the presynaptic membrane-associated protein SNAP-25 (Schiavo et al., 2000 Simpson, 2004). Serotype Cl is unique in that it cleaves two cytoplasmic proteins, syntaxin and SNAP-25 (Wiltiamson et al., 1996). Interaction of these SNAREs on the surface of synaptic vesicles and active zone membranes is required for voltage- and Ca " -dependent release of neurotransmitter cleavage by BoNT inhibits this process, leading to muscle weakness and paralysis (Sutton et al., 1998 Schiavo et al., 2000). Cleavage of SNARE proteins appears to be sufficient to account for all actions of the BoNTs, and the SNARE hypothesis has received near universal acceptance since its introduction in the early 1990s. 

Yamasaki, S., Baumeister, A., Binz, T., Blasi, J., Link, E., Cornihe, F., Roques, B., Fykse, E.M., Sudhof, T.C., and Jahn, R. 1994. Cleavage of members of the synaptobrevin/VAMP family by types D and F botulinal neurotoxins and tetanus toxin. J. Biol. Chem. 269 12764—12772. 

Serotypes B, D, F, and G cleave different sites on the synaptic vesicle protein, synaptobrevin (VAMP), whereas serotypes A and E cleave the presynaptic membrane-associated protein SNAP-25. Serotype Cl is unique in that it cleaves two cytoplasmic proteins, syntaxin and SNAP-25. Interaction of these proteins (designated as SNARE) on the surface of synaptic vesicles and active zone membranes is... 

All botulin neurotoxins act in a similar way. They only differ in the amino-acid sequence of some protein parts (Prabakaran et al., 2001). Botulism symptoms are provoked both by oral ingestion and parenteral injection. Botulin toxin is not inactivated by enzymes present in the gastrointestinal tracts. Foodborne BoNT penetrates the intestinal barrier, presumably due to transcytosis. It is then transported to neuromuscular junctions within the bloodstream and blocks the secretion of the neurotransmitter acetylcholine. This results in muscle limpness and palsy caused by selective hydrolysis of soluble A-ethylmalemide-sensitive factor activating (SNARE) proteins which participate in fusion of synaptic vesicles with presynaptic plasma membrane. SNARE proteins include vesicle-associated membrane protein (VAMP), synaptobrevin, syntaxin, and synaptosomal associated protein of 25 kDa (SNAP-25). Their degradation is responsible for neuromuscular palsy due to blocks in acetylcholine transmission from synaptic terminals. In humans, palsy caused by BoNT/A lasts four to six months. 

Schiavo, G., Malizio, C., Trimble, W.S., Polverino de Laureto, P., Milan, G., Sugiyama, H., Johnson, E.A. and Montecucco, C., Botulinum G neurotoxin cleaves VAMP/synaptobrevin at a single Ala-Ala peptide bond, J. Biol. Chem., 269, 20213-20226, 1994. 

Schiavo, G., Shone, C.C., Rossetto, O., Alexander, F.C. and Montecucco, C., Botulinum neurotoxin serotype 1 is a zinc endopeptidase specific for VAMP/ synaptobrevin, J. Biol. Chern., 268, 11516-11519, 1993. 

The SNAREs involved in the fusion of synaptic vesicles and of secretory granules in neuroendocrine cells, referred to as neuronal SNAREs, have been intensely studied and serve as a paradigm for all SNAREs. They include syntaxin 1A and SNAP-25 at the presynaptic membrane and synaptobrevin 2 (also referred to as VAMP 2) at the vesicle membrane. Their importance for synaptic neurotransmission is documented by the fact that the block in neurotransmitter release caused by botulinum and tetanus neurotoxins is due to proteolysis of the neuronal SNAREs (Schiavo et al. 2000). Genetic deletion of these SNAREs confirmed their essential role in the last steps of neurotransmitter release. Intriguingly, analysis of chromaffin cells from KO mice lacking synaptobrevin or SNAP-25 showed that these proteins can be at least partially substituted by SNAP-23 and cellubrevin, respectively (Sorensen et al. 2003 Borisovska et al. 2005), i.e., the corresponding SNAREs involved in constitutive exocytosis. 

In neurons, the SNARE complex consists of three main proteins the v-SNARE synaptobrevin or VAMP (vesicle-associated membrane protein), and two t-SNAREs, syntaxin and SNAP-25 (synaptosomal associated protein of 25 kD). Synaptobrevins traverse the synaptic vesicle membrane in an asymmetric manner a few amino acids are found inside the vesicle, but most of the molecule lies outside the vesicle, within the cytoplasm. Synaptobrevin makes contact with another protein anchored to the plasma membrane of the presynaptic neuron, syntaxin, which is associated with SNAP-25. Via these interactions, the SNARE proteins play a role in the docking and fusion of synaptic vesicles to the active zone. 

Stimulus-evoked, calcium-dependent release of acetylcholine (ACh) from the cholinergic synapse normally occurs through the formation of a fusion complex between ACh-containing vesicles and the intracellular leaflet of the nerve terminal membrane (Amon et al., 2001). This synaptic vesicle fusion complex consists of several proteins of the SNARE family, including a 25 kDa synaptosomal associated protein (SNAP-25), vesicle-associated membrane protein (VAMP, or synaptobrevin), and the synaptic membrane protein syntaxin. Other SNARE proteins have been identified as components of membrane transport systems in yeast and mammals but have not been implicated as targets for BoNTs. Meanwhile, type A and E neurotoxins cleave SNAP-25 while types B, D, F, and G act on VAMP and type C1 toxin cleaves both syntaxin and SNAP-25. Neurotoxin-mediated cleavage of any of these substrates disrupts the processes involved in the exocytotic release of ACh and leads to flaccid paralysis of the affected skeletal muscles. 

Protease-free preparations of TeTx and BoNT/B, D, F and G cleave a membrane protein of small synaptic vesicles (SSV) called VAMP or synaptobrevin (Schiavo ef ai, 1992 a, 1993 a,c, Yamasaki et ai, 1994 a, b). Conversely, BoNT/A, C and E act on proteins associated with the presynaptic membrane BoNT/A and E cut SNAP-25, while serotype C cleaves syntaxin, in addition to SNAP-25 (Blasi efai, 1993 a, b ... 

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