Forms non-fusogenic complexes with SNAP25 and STX1A and may thereby modulate the formation of functional SNARE complexes and exocytosis. Part of a ternary complex containing SNAP25 and STX1A that can be dissociated by NAPA and NSF. Interacts with STX4A. Detected at low levels in brain, and at very low levels in heart, adrenal gland, testis, liver and kidney. May be due to an intron retention. May be due to an intron retention.