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 (PubMed:12556468). Found in a complex with VAMP8 and STX1A (PubMed:12130530). Found in a complex with VAMP8 and STX4 in pancreas (By similarity). Interacts simultaneously with SNAPIN and SYN4 (By similarity). Interacts with STX1A (By similarity). Interacts with STX12 (By similarity). Interacts tightly to multiple syntaxins and synaptobrevins/VAMPs (By similarity). Interacts with ZDHHC13 (via ANK repeats) (By similarity). Interacts with ZDHHC17 (via ANK repeats) (PubMed:28882895). Mainly localized to the plasma membrane. Ubiquitous. Highest levels where found in placenta. Belongs to the SNAP-25 family.