Component of NMDA receptor complexes that function as heterotetrameric, ligand-gated ion channels with high calcium permeability and voltage-dependent sensitivity to magnesium. Channel activation requires binding of the neurotransmitter glutamate to the epsilon subunit, glycine binding to the zeta subunit, plus membrane depolarization to eliminate channel inhibition by Mg(2+) (PubMed:1377365, PubMed:26912815). Sensitivity to glutamate and channel kinetics depend on the subunit composition (PubMed:1377365). In concert with DAPK1 at extrasynaptic sites, acts as a central mediator for stroke damage. Its phosphorylation at Ser-1303 by DAPK1 enhances synaptic NMDA receptor channel activity inducing injurious Ca2+ influx through them, resulting in an irreversible neuronal death (PubMed:20141836). Contributes to neural pattern formation in the developing brain (PubMed:8789948). Plays a role in long-term depression (LTD) of hippocampus membrane currents and in synaptic plasticity (PubMed:8789948). Heterotetramer. Forms heterotetrameric channels composed of two zeta subunits (GRIN1), and two epsilon subunits (GRIN2A, GRIN2B, GRIN2C or GRIN2D) (in vitro) (PubMed:1377365, PubMed:26912815). Can also form heterotetrameric channels that contain at least one zeta subunit (GRIN1), at least one epsilon subunit, plus GRIN3A or GRIN3B (PubMed:12008020, PubMed:14602821). In vivo, the subunit composition may depend on the expression levels of the different subunits (Probable). Found in a complex with GRIN1, GRIN3A and PPP2CB (By similarity). Found in a complex with GRIN1 and GRIN3B (PubMed:12008020, PubMed:14602821). Interacts with MAGI3 (By similarity). Interacts with HIP1 and NETO1 (PubMed:17329427, PubMed:19243221). Interacts with PDZ domains of PATJ, DLG3 and DLG4. Interacts with DAPK1 (PubMed:20141836). Found in a complex with GRIN1 and PRR7. Interacts with PRR7 (By similarity). Interacts with CAMK2A (By similarity). Interacts with ARC; preventing ARC oligomerization (By similarity). Interacts with TMEM25 (PubMed:31424425). Co-localizes with the motor protein KIF17 along microtubules. Detected in brain (at protein level) (PubMed:8789948). Detected throughout the brain, and in brain stem trigeminal nucleus (PubMed:8789948). Detected in forebrain (PubMed:1377365). A hydrophobic region that gives rise to the prediction of a transmembrane span does not cross the membrane, but is part of a discontinuously helical region that dips into the membrane and is probably part of the pore and of the selectivity filter. Phosphorylated on tyrosine residues (PubMed:12451687). Phosphorylation at Ser-1303 by DAPK1 enhances synaptic NMDA receptor channel activity (PubMed:20141836). Mutant pups are born at the expected Mendelian rate and appear grossly normal, but lack suckling behavior. As a consequence, all die shortly after birth, except when they are fed manually via a soft tube that delivers milk directly into the stomach. While mutant neonate brain structures are grossly normal, the mutant brain stem trigeminal complex lacks the neural repeating units called barrelettes that correspond to whisker-associated nerve fibers. Primary afferent nerve fibers from whiskers fail to show normal clustering in the region where barrelette structures form in wild-type. In contrast, nasolabial motor neurons appear normal. Contrary to wild-type neonates, brain slices from the mutant neonate hippocampus CA1 region lack NMDA receptor-type ion channel activity. Contrary to wild-type pups, prolonged low frequency stimulation of afferent fibers does not induce long-term depression (LTD) in the hippocampus. Belongs to the glutamate-gated ion channel (TC 1.A.10.1) family. NR2B/GRIN2B subfamily.