Component of N-methyl-D-aspartate (NMDA) receptors (NMDARs) that function as heterotetrameric, ligand-gated cation channels with high calcium permeability and voltage-dependent block by Mg(2+) (PubMed:26875626, PubMed:27616483, PubMed:28126851, PubMed:9489750). Participates in synaptic plasticity for learning and memory formation (By similarity). Channel activation requires binding of the neurotransmitter L-glutamate to the GluN2 subunit, glycine or D-serine binding to the GluN1 subunit, plus membrane depolarization to eliminate channel inhibition by Mg(2+) (PubMed:26875626, PubMed:27616483, PubMed:28126851, PubMed:9489750). NMDARs mediate simultaneously the potassium efflux and the influx of calcium and sodium (By similarity). Each GluN2 subunit confers differential attributes to channel properties, including activation, deactivation and desensitization kinetics, pH sensitivity, Ca2(+) permeability, and binding to allosteric modulators (PubMed:26875626, PubMed:28095420, PubMed:28126851, PubMed:9489750). {ECO:0000250|UniProtKB:P35438, ECO:0000250|UniProtKB:Q14957, ECO:0000269|PubMed:26875626, ECO:0000269|PubMed:27616483, ECO:0000269|PubMed:28095420, ECO:0000269|PubMed:28126851, ECO:0000269|PubMed:9489750}. This is the function of GRIN2D (glutamate ionotropic receptor NMDA type subunit 2D, ENSG00000105464).