Required for perception of chronic pain through NMDA receptor signaling. Regulates surface expression of NMDA receptors in dorsal horn neurons of the spinal cord. Interacts with the cytoplasmic tail of NMDA receptor subunits as well as inward rectifying potassium channels. Involved in regulation of synaptic stability at cholinergic synapses. Part of the postsynaptic protein scaffold of excitatory synapses. Interacts with NOS1/nNOS through second PDZ domain. Interacts with KCNJ2/Kir2.1 (via C-terminus) through one of its PDZ domains (By similarity). Interacts with KCNJ4 (PubMed:11997254). Interacts with FRMPD4 (via C-terminus) (By similarity). Interacts through its PDZ domains with NETO1 (PubMed:19243221). Interacts with LRFN1, LRFN2 and LRFN4. Interacts with FASLG (By similarity). Interacts with KCNJ4 (By similarity). Interacts with ADAM22 (PubMed:20089912). Interacts with DGKI (via PDZ-binding motif) (By similarity). Concentrated in soma and postsynaptic density of a subset of neurons. Brain. Highest levels of isoform 1 in cortex, olfactory bulb, thalamus, hypothalamus, striatum and hippocampus. Highest level of isoform 2 in olfactory bulb. Reduced levels in cortex and hippocampus. Highest level of isoform 4 in spinal cord. Low levels of isoform 4, isoform 6, and isoform 7 in superior cervical ganglion. Isoform 7 has an L27 domain close to N-terminus. Palmitoylation of isoform 1 and isoform 2 is not required for targeting to postsynaptic density. Mice do not respond to persistent pain. Postsynaptic surface expression of NMDA receptors and NMDA receptor-mediated synaptic function are reduced in dorsal horn neurons of the spinal chord. Incomplete sequence.