Involved in the targeting and/or fusion of transport vesicles to their target membrane (PubMed:12364587, PubMed:22270918). Major SNARE protein of synaptic vesicles which mediates fusion of synaptic vesicles to release neurotransmitters (PubMed:9482790, PubMed:12364587). Essential for fast vesicular exocytosis and activity-dependent neurotransmitter release as well as fast endocytosis that mediates rapid reuse of synaptic vesicles (PubMed:12364587). Also involved in a neuron-specific sort-and-degrade mechanism that promotes endolysosomal degradation and is required for neuronal maintenance (PubMed:22270918). Part of the SNARE core complex containing Snap25 and syntaxin. Localizes to synaptic vesicles and to a subset of early endosomal compartments, predominantly at synapses. Specifically expressed in neurons and synapses. Transcripts are first detectable at stage 13 or 14 (PubMed:8229205). The expression is restricted to the nervous system, becoming quite robust in both the central and peripheral nervous system (CNS and PNS, respectively) by late embryogenesis (PubMed:8229205). Embryos develop normally, but their nerve terminals do not release transmitter in response to an action potential (PubMed:9482790). Spontaneous neurotransmitter release is reduced, but not abolished (PubMed:9482790, PubMed:10460261). Slow degeneration in adult photoreceptor neurons is also observed: defects are caused by an accumulation of endosomal vesicles, leading to transmembrane protein degradation defects and a secondary increase in autophagy (PubMed:22270918). Belongs to the synaptobrevin family.