Involved in the targeting and/or fusion of transport vesicles to their target membrane (By similarity). Major SNARE protein of synaptic vesicles which mediates fusion of synaptic vesicles to release neurotransmitters. Essential for fast vesicular exocytosis and activity-dependent neurotransmitter release as well as fast endocytosis that mediates rapid reuse of synaptic vesicles (By similarity) (PubMed:30929742). Modulates the gating characteristics of the delayed rectifier voltage-dependent potassium channel KCNB1.