Required to anchor acetylcholinesterase (ACHE) to the basal lamina of the neuromuscular junction and to the membrane of neuronal synapses in brain. Organizes ACHE into tetramers (By similarity). Interacts with ACHE, probably through disulfide bonds. In the brain, PRIMA linked to ACHE is found in membrane rafts. Isoforms 1 and 2 are expressed in the adult brain. In matured cortical neurons, only isoform 1 is detectable. Up-regulated during the differentiation of in vitro cultured cortical neurons. The proline-rich attachment domain (PRAD) binds the AChE catalytic subunits.