Vesicle-associated membrane protein (VAMP) or Synaptobrevin, a type II membrane protein of small synaptic vesicles, is essential for neuroexocytosis because its proteolysis by tetanus and botulinum neurotoxins types B, D, F and G blocks neurotransmitter release 1.
Synaptobrevin is a synaptic vesicle protein that has an essential role in exocytosis and forms the SNARE complex with syntaxin and SNAP-25 2.
Baumert et al., discovered synaptobrevin, a membrane protein of small synaptic vesicles with a mol. wt of 18 kDa and published a preliminary report on their work in 1988 3.
Neurotransmitter release occurs when synaptic vesicles fuse with the plasma membrane. A crucial step in this process involves the assembly of a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex, a highly stable, parallel four-helix bundle formed between the synaptic vesicle SNARE synaptobrevin 2 (syb2) and the plasma membrane SNAREs syntaxin 1 and synaptosome-associated protein of 25 kDa (SNAP-25) 4.
Mode of Action
The mechanisms responsible for SNARE complex multimerization remains controversial. Initial studies suggested that multimerization of synaptic SNARE complexes could be achieved via domain swapping, whereby one of the two SNAP-25 helices could be substituted by the equivalent helix from a neighboring complex. Alternative models proposed the involvement of accessory proteins, such as synaptotagmin or complexin, or the transmembrane domains of syb2 and syntaxin 1A, in synaptic SNARE complex multimerization. However, SNARE complexes assembled from recombinant coils and lacking transmembrane domains are able to associate with each other, arguing that at least some of the interactions that support multimerization may require neither accessory proteins nor transmembrane domains. The precise multimeric nature and configuration of these recombinant cytosolic SNARE complexes is ambiguous. Conflicting results have been reported, ranging from dimers involving C-terminal residues of at least one of the two monomers, to mixtures of monomers/trimers in solution 4.
Several protein components thought to be involved in docking and fusion of SSV (small synaptic vesicle) with the presynaptic membrane have been identified, although the actual process of exocytosis remains obscure. VAMP plays an important role in the process. Indeed, when it is cleaved by the zinc endopeptidase activity of tetanus neurotoxin (TeNT) and botulinum neurotoxin (BoNT), types B, D, F and G, neuroexocytosis is blocked. In addition, VAMP is a member of the putative membrane fusion complex. VAMP has been suggested to play the role of vesicle receptor (SNARE) (SNAP, soluble NSF attachment protein) in the process of vesicle docking to the active zones of the presynaptic membrane, where syntaxin and SNAP-25 (synaptosomal associated protein of 25 kDa) would play the corresponding role of target membrane receptors (t-SNAREs) 1.
In the kidney collecting duct, water reabsorption is regulated by exocytotic insertion and endocytotic retrieval of the water channel aquaporin 2 (AQP2). AQP2 resides in intracellular vesicles that fuse with the apical membrane of collecting duct principal cells in the presence of the antidiuretic hormone vasopressin. The SNARE protein VAMP/synaptobrevin-2 (VAMP-2) is functionally involved in cAMP-stimulated AQP2 translocation in renal collecting duct cells. It has been suggested that VAMP-2 plays a major role in the mechanism of vesicle trafficking 5.
The tetanus and botulinum B toxins block neurotransmitter release by cleaving the synaptic vesicle protein synaptobrevin-2. Two peptides containing this cleavage site have been shown to inhibit the in vitro proteolysis of synaptobrevin-2 by both toxins 6.
1. Washbourne P, Schiavo G, Montecucco C (1995). Vesicle-associated membrane protein-2 (synaptobrevin-2) forms a complex with synaptophysin. Biochem. J., 305(3): 721-724.
2. Hazzard J, Südhof TC, Rizo J (1999). NMR analysis of the structure of synaptobrevin and of its interaction with Syntaxin. Journal of Biomol NMR., 14(3): 203-207.
3. Baumert M, Maycox PR, Navone F, De Camilli P, Jahn R (1989). Synaptobrevin: an integral membrane protein of 18 000 daltons present in small synaptic vesicles of rat brain. The EMBO J., 8(2):379-84..
4. Fdez E, Jowitt TA, Wang MC, Rajebhosale M, Foster K, Bella J, Baldock C, Woodman PG, Hilfiker S (2008). A Role for Soluble N-Ethylmaleimide-sensitive Factor Attachment Protein Receptor Complex Dimerization during Neurosecretion Mol. Biol. Cell., 2008 19(8):3379-3389.
5. Gouraud S, Laera A, Calamita G, Carmosino M, Procino G, Rossetto O, Mannucci R, Rosenthal W, Svelto M, Valenti G (2002). Functional involvement of VAMP/synaptobrevin-2 in cAMP-stimulated aquaporin 2 translocation in renal collecting duct cells J Cell Sci., 115(18), 3667-3674.
6. Schiavo G, Benfenati F, Poulain B, Rossetto O, Polverino de Laureto P, DasGupta BR, Montecucco C. 1992. Tetanus and botulinum-B neurotoxins block neurotransmitter release by proteolytic cleavage of synaptobrevin. Nature, 359(6398):832-835.
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