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Any of a family of proteins that facilitate fusion between intracellular transport vesicles and the plasma membrane (or other target membrane) and are essential for secretion of cellular materials by exocytosis. Each has a characteristic SNARE motif of 60–70 amino acids, which can associate with similar motifs in other SNAREs to form a SNARE complex. SNARE proteins are vital for normal release of neurotransmitter from synaptic vesicles at the active zones of synapses. Essentially, SNARE proteins in the vesicle membrane (v-SNARES) form a complex with other SNARE proteins in the target membrane (t-SNARES), which leads to docking of the vesicle, fusion of the membranes, and formation of a fusion pore, allowing the contents of the vesicle to escape. The principal v-SNARE is synaptobrevin (belonging to a family called vesicle-associated membrane proteins, or VAMPs). The first step involves activation of the SNARE proteins by N-ethymaleimide-sensitive factor (NSF), soluble NSF attachment protein (SNAP), and ATP. Then, following tethering of the vesicle to its target membrane by a protein called RAB1, synaptobrevin associates with two t-SNARES, called syntaxin and SNAP-25 (synaptosome-associated protein of 25 kDa), to form a SNARE complex; this causes the vesicle to become irreversibly docked with the target membrane. A further protein, synaptotagmin, is recruited; this is sensitive to the presence of calcium ions (Ca2+) and is thought to act as a switch mechanism, regulating the completion of membrane fusion in response to the influx of Ca2+ions through calcium channels, and subsequent dissociation of the SNARE complex. Tetanus and botulinum toxins are proteases that degrade components of the SNARE complex, hence their potent effects on nerve function.

Subjects: Biological Sciences.

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