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:16214956, PubMed:19524674, PubMed:21677647, PubMed:25008524, PubMed:26912815, PubMed:27135925, Ref.11, PubMed:28232581). Sensitivity to glutamate and channel kinetics depend on the subunit composition (Probable). Channel activity is modulated by zinc ions. The activity of the heterotetramer with grin2b is stimulated by micromolar levels of Zn(2+) (PubMed:19524674). The activity of the heterotetramer with grin2a is inhibited by nanomolar levels of Zn(2+) (Ref.11). Heterotetramer (PubMed:27062927). Forms heterotetrameric channels composed of two zeta subunits (grin1), and two epsilon subunits (grin2a, grin2b, grin2c or grin2d) (in vitro) (PubMed:16214956, PubMed:19524674, PubMed:21677647, PubMed:25008524, PubMed:26912815, PubMed:27135925, Ref.11, PubMed:28232581). Does not form functional channels by itself (PubMed:16214956). In vivo, the subunit composition may depend on the expression levels of the different subunits (Probable). 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. Belongs to the glutamate-gated ion channel (TC 1.A.10.1) family. NR1/GRIN1 subfamily.