Amyloid beta A4 precursor protein-binding family A member 1 (APBA1) functions in synaptic vesicle exocytosis by binding to Munc18-1, an essential component of the synaptic vesicle exocytotic machinery. APBA1 modulates processing of the beta-amyloid precursor protein (APP) and hence formation of beta-APP. APBA1 is composed of an N-terminal domain that binds Munc18-1 and LIN-2/CASK, a middle phosphotyrosine-binding domain (PID/PTB) that mediates binding with the cytoplasmic domain of the beta-amyloid precursor protein, and two C-terminal PDZ domains thought to attach proteins to the plasma membrane.