Plays a role in the maintenance of lens transparency, and may also play a role in muscle cell strength (PubMed:25757569, PubMed:27734846). Involved in hippocampal neurite branching and neuromuscular junction formation, as a result plays a role in spatial memory functioning (PubMed:27734846). Activates transcription of APP (By similarity). Interacts (via C-terminus) with APP (via C-terminus) (PubMed:18650440). Interacts with APLP2 (via cytoplasmic domain) (By similarity). Expressed in the brain, retinal lens and muscle cells (at protein level). Knockout mice develop cataracts from 16 months of age with defects such as ulcer-like anomalies in the cornea, and opacity in the lens cortex or wider lens. Decreased muscle strength, however clasping ability is unaffected (PubMed:25757569). Impaired spatial memory retrieval and learning (PubMed:27734846). Reduced branching of hippocampal neurites and increased fragmentation of neuromuscular junctions (PubMed:27734846). APBB1 and APBB2 double knockout mice show progressive retinal lens disruption from 1 month of age, morphologically lenses show massive vacuolization, lens capsule rupture and disruption of the lens fiber cells organization. Decreased muscle strength, however clasping ability is unaffected (PubMed:25757569, PubMed:27734846). Defects in peripheral motor function including balance and coordination, reduced environmental anxiety, reduced hippocampal basal synaptic transmission and synaptic plasticity (PubMed:27734846).