Putative function in synaptic vesicle exocytosis by binding to STXBP1, an essential component of the synaptic vesicle exocytotic machinery. May modulate processing of the amyloid-beta precursor protein (APP) and hence formation of APP-beta. Part of a multimeric complex containing STXBP1 and syntaxin-1. Binds to the cytoplasmic domain of amyloid-beta protein, and to the nuclear factor NF-kappa-B/p65 via its PDZ domain. Interacts with the N-terminal domain of NECAB3. Brain. Composed of an N-terminal domain that binds STXBP1, a middle phosphotyrosine-binding domain (PID/PTB) that mediates binding with the cytoplasmic domain of the amyloid-beta precursor protein, and two C-terminal PDZ domains thought to attach proteins to the plasma membrane.