Synaptobrevin is a membrane-anchored SNARE protein associated with secretory vesicles, including synaptic vesicles. Its cytosolic helix joins complementary helices from syntaxin and SNAP-25 to form a SNARE complex. When the partners initially occupy opposing lipid bilayers, their assembly helps bring those lipid bilayers close enough for membrane fusion. The protein helps couple the membranes mechanically; it is not a pore through which the neurotransmitter simply leaks. [ref]
Molecular Biology of the Cell, 4th edition by Bruce Alberts and others. Chapter 13, Molecular Mechanisms of Vesicle Budding and Fusion
Reconstituting synaptobrevin and its complementary SNARE proteins into separate liposomes made fusion measurable outside a cell. The ability to accumulate docked intermediates at low temperature and trigger fusion on warming also distinguished membrane docking from the subsequent merger. Living synapses add regulation that this minimal assay does not reproduce. [ref]
SNAREpins: minimal machinery for membrane fusion by T. Weber and others. 1998, abstract: recombinant v- and t-SNAREs and temperature-dependent intermediates
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