Enables syntaxin-1 binding activity. Involved in synaptic vesicle exocytosis. Located in dendrite; neuronal cell body; and synapse. Part of synaptobrevin 2-SNAP-25-syntaxin-1a-complexin I complex. Is active in postsynapse and presynapse. Human ortholog(s) of this gene implicated in developmental and epileptic encephalopathy 63. Orthologous to human CPLX1 (complexin 1). [provided by Alliance of Genome Resources, Apr 2022]