MPDZ is a 2,042 amino acid peripheral membrane protein that colocalizes with SR-2C on the apical membrane of epithelial choroid plexus cells. Expressed in heart, brain, placenta, liver, skeletal muscle, kidney and pancreas, MPDZ causes clustering of SR-2C, a serotonin receptor, at the cell surface. MPDZ is member of the NMDAR signaling complex that is involved in regulating AMPAR potentiation and synaptic plasticity in excitatory synapses. As a tight junction protein in epithelial cells, MPDZ interacts with SSTR3, a G-protein-coupled receptor, to regulate transepithelial permeability in a pertussis toxin sensitive manner. MPDZ, along with Kir4.2, may form a complex with other proteins in the nephron and regulate ion transport. MPDZ contains one L27 domain and thirteen PDZ domains.