Essential component of the high affinity receptor for the general membrane fusion machinery and an important regulator of transport vesicle docking and fusion. Homotetramer (via coiled-coil domain), also forms heterotetramers with STX4 and VAMP3 (By similarity). Found in a complex with VAMP8 and STX1A (By similarity). Found in a complex with VAMP8 and STX4 in pancreas (PubMed:15363411). Interacts simultaneously with SNAPIN and SYN4 (By similarity). Interacts with STX1A (PubMed:9507000). Interacts with STX12 (PubMed:9507000). Interacts tightly to multiple syntaxins and synaptobrevins/VAMPs (By similarity). Interacts with ZDHHC13 (via ANK repeats) (PubMed:26198635). Interacts with ZDHHC17 (via ANK repeats) (PubMed:26198635). Mainly localized to the plasma membrane. Expressed in non-neuronal tissues. (Microbial infection) Targeted and hydrolyzed by C.botulinum neurotoxin type A (BoNT/A, botA) which hydrolyzes the 202-Thr-|-Arg-203 bond; the in vitro reaction is not highly efficient (PubMed:9886085). (Microbial infection) Targeted and hydrolyzed by C.botulinum neurotoxin type E (BoNT/E) which hydrolyzes the 185-Arg-|-Ile-186 bond; the in vitro reaction is more efficient than that of BoNT/A (PubMed:9886085). Belongs to the SNAP-25 family.