Member of the NMDAR signaling complex that may play a role in control of AMPAR potentiation and synaptic plasticity in excitatory synapses (By similarity). Promotes clustering of HT2RC at the cell surface (By similarity). Interacts with CLDN5, DLG4, GRIN1, SYNGAP1, CAMK2A and CAMK2B, HTR2A, HTR2B, HTR2C, PLEKHA1/TAPP1 and PLEKHA2/TAPP2 (By similarity). Interacts with F11R/JAM, CLDN1, NG2, CXADR, CRB1, MPP4 and PALS1. Interacts with FAT4 (via cytoplasmic domain). Interacts with DLL1 (PubMed:15509766). Colocalizes with HTR2C on the apical membrane of epithelial choroid plexus cells. Highly enriched in postsynaptic densities (PSD) (By similarity). Localized to punctae on dendrites of hippocampal neurons and colocalizes with the synaptic marker DLG4. Enriched at the tight junctions of epithelial cells. Association to the tight junctions depends on CXADR (By similarity). In the retina, localizes to the sub-apical region adjacent to the adherens junction complex at the outer limiting membrane. Localized mainly in the Schmidt-Lanterman incisures of myelinating Schwann cells. In the brain, it is strongly expressed in the choroid plexus. Within the hippocampal formation, strongest expression was seen in the soma of CA1-4 pyramidal cells. Expressed in most neocortical regions with the strongest expression in piriform cortex and amygdaloid nuclei but also detected in the subiculum and olfactory bulb. In the cerebellum, the highest level of expression was found in Purkinje cells. Moderately expressed in the granular layer and molecular layer. Expressed in the pontine nuclei, parts of spinal trigeminal nuclei, and the principal sensory trigeminal nuclei of the metencephalon. Expressed in all thalamic and hypothalamic nuclei, and the substantia nigra (at protein level). Ubiquitously expressed. Expressed at the outer limiting membrane of the retina at 3 months of age. The PDZ domain 2 mainly binds CAMK2A and CAMK2B. The PDZ domains 7 and 10 bind the Ad9 E4-ORF1 oncoprotein. The PDZ domain 10 binds the C-terminal PDZ-binding motif of HTR2C. The PDZ domains 10 and 13 bind PLEKHA1 and PLEKHA2. The PDZ domain 13 binds SYNGAP1 (By similarity). The PDZ domain 1 binds NG2. The PDZ domain 9 binds F11R. The PDZ domain 10 binds the C-terminus of CLDN1 and KIT. The PDZ domain 13 binds CXADR. Probable cloning artifact.