What is the function of synaptobrevin?

ANSWER: (A) Presynaptic vesicle fusionREF: Ganongs 23rd Ed page 116-119, European Journal of Biochemistry Volume 249 Issue 2 page 540-546Synaptobrevins./VAMPs (vesicle associated membrane protein)represents a family of integral membrane proteins of 11-13 kDa with the N-terminal region exposed to the cytoplasm and a C-terminal transmembrane domain. Synaptobrevin/VAMP is an essential component of the exocytotic fusion machine, related to a larger protein family referred to as v-SNAREs. The primary role of SNARE proteins is to mediate vesicle fusion, that is, the exocytosis of cellular transport vesicles with the cell membrane at the porosome or with a target compartment (such as a lysosome).Two isoforms were identified in the mammalian CNSSynaptobrevin 1 (VAMP 1 or pl8-l); Synaptobrevin 1 is highly conserved between vertebrates and invertebrates. It is a major constituent of synaptic vesicles and peptidergic secretory granules in all neurons examined so far. In addition, it is present on secretory granules of neuroendocrine cells.Synaptobrevin 2 (VAMP 2 or pi 8-2) that differ in their distribution within different brain regions. Low levels of synaptobrevin 2 are present In many other tissues where the protein resides on specialized microvesicles.In non-neuronal cells the third isoform, cellubrevin (VAMP 3), is present where it is localized to an endosomal membrane pool.SNAREs can be divided into two categories: vesicle or v-SNAREs, which are incorporated into the membranes of transport vesicles during budding, and target or t-SNAREs, which are located in the membranes of target compartments. In synaptic transmission, vesicles are proposed to dock at presynaptic active zones by the association of synaptobrevin (v-SNARE) with syntaxin (t-SNARE) in a Ca+- triggered process.Note:Tetanus toxin and botulinum toxins B, D, F, and G act on synaptobrevinBotulinum toxin C acts on syntaxinin