Potentially involved in docking of synaptic vesicles at presynaptic active zones. Apical receptor involved in membrane fusion of apical vesicles. Essential for survival of retinal photoreceetors. Interacts with REEP6 (By similarity). Interacts with PRPH2 in rod and cone photoreceptors (By similarity). Interacts with ROM1 (By similarity). Interacts with SNAP25 (By similarity). Interacts with VAMP2 (By similarity). Localized to the inner and outer plexiform layers, the cell body and the inner segments of photoreceptors. Heart, spleen, lung and kidney. Belongs to the syntaxin family.