Enables syntaxin-1 binding activity. Involved in positive regulation of exocytosis; regulation of synaptic vesicle exocytosis; and regulation of synaptic vesicle priming. Acts upstream of or within exocytosis and regulation of exocytosis. Part of acetylcholine-gated channel complex. Is active in hippocampal mossy fiber to CA3 synapse and presynapse. Is extrinsic component of neuronal dense core vesicle membrane. Orthologous to human STXBP5 (syntaxin binding protein 5). [provided by Alliance of Genome Resources, Apr 2022]