Induces KLC1 association with vesicles and functions as a cargo in axonal anterograde transport. Complex formation with APBA2 and APP, stabilizes APP metabolism and enhances APBA2-mediated suppression of beta-APP40 secretion, due to the retardation of intracellular APP maturation. In complex with APBA2 and C99, a C-terminal APP fragment, abolishes C99 interaction with PSEN1 and thus APP C99 cleavage by gamma-secretase, most probably through stabilization of the direct interaction between APBA2 and APP. As intracellular fragment AlcICD, suppresses APBB1-dependent transactivation stimulated by APP C-terminal intracellular fragment (AICD), most probably by competing with AICD for APBB1-binding. May modulate calcium-mediated postsynaptic signals. Directly interacts with APBA2. Forms a tripartite complex with APBA2 and APP. The CTF1 chain interacts with PSEN1. The intracellular fragment AlcICD interacts with APBB1; this interaction stabilizes AlcICD metabolism. Interacts with KLC1 and APBB1. Neurite tips. Localized in the postsynaptic membrane of both excitatory and inhibitory synapses. The AlcICD fragment is translocated to the nucleus upon interaction with APBB1 (By similarity). Highly expressed in the brain (at protein level), with over 90% of the neurons expressing detectable amounts. In the brain, relatively high levels in the cerebral cortex, striatum, hippocampus and thalamus. Moderate levels in the cerebellum. Low levels in the olfactory bulb, midbrain and pons (at protein level). Not detected in Purkinje cells. Expressed at low levels in the lung (at protein level). At the mRNA level, weakly detected in the kidney, lung, skeletal muscle, heart and testis. Not expressed in the sciatic nerve fiber. Expression in the brain gradually increases during the first postnatal week, reaching a peak at P7. In the gray matter, highly expressed in both developing and adult brain. In the white matter, at P6 highly expressed in all major fiber tracts, including the anterior commissure and the corpus callosum, as well as the external and internal capsules, while in the adult, axonal expression in fiber tracts is only faint (at protein level). The cytoplasmic domain is involved in interaction with APBA2, as well as the binding of synaptic Ca(2+). Proteolytically processed under normal cellular conditions. A primary zeta-cleavage generates a large extracellular (soluble) N-terminal domain (sAlc) and a short C-terminal transmembrane fragment (CTF1). A secondary cleavage catalyzed by presenilin gamma-secretase within the transmembrane domain releases the beta-Alc-alpha chain in the extracellular milieu and produces an intracellular fragment (AlcICD). Beta-Alc-alpha secretion is largely dependent upon PSEN1 and PSEN2. This processing is strongly suppressed in the tripartite complex formed with APBA2 and APP, which seems to prevent the association with PSEN1. Extended N-terminus.