May modulate calcium-mediated postsynaptic signals. 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. Directly interacts with APBA2. Forms a tripartite complex with APBA2 and APP. Interacts with low affinity with KLC1 (By similarity). Most prominent in the postsynaptic specializations of asymmetric (type I) synapses with both axodendritic and axospinous localization. According to PubMed:12498782, expressed predominantly in the brain and in kidney. Low levels in heart, skeletal muscle, liver, placenta, pancreas and lung. According to PubMed:12972431, predominant expression in brain, and only marginal in kidney. In brain, present throughout all cortical layers, highest levels in GABAergic neurons (based on morphology and distribution pattern). Binds synaptic Ca(2+) with its cytoplasmic domain. 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 gamma-secretase within the transmembrane domain releases the beta-Alc-beta chain in the extracellular milieu and produces an intracellular fragment (AlcICD). This processing is strongly suppressed in the tripartite complex formed with APBA2 and APP, which seems to prevent the association with gamma-secretase (By similarity). Extended N-terminus.