Potentially involved in docking of synaptic vesicles at presynaptic active zones. May mediate Ca(2+)-regulation of exocytosis acrosomal reaction in sperm (By similarity). Interacts with OTOF. Interacts with SYT6 and SYT8; the interaction is Ca(2+)-dependent (By similarity). Phosphorylated by CK2. Belongs to the syntaxin family.