This is a very short highly conserved domain that is C-terminal to the cytosolic transmembrane region IV of the NMDA-receptor 1. It has been shown to bind Calmodulin-Calcium with high affinity. The ionotropic N-methyl-D-aspartate receptor (NMDAR) is a major source of calcium flux into neurons in the brain and plays a critical role in learning, memory, neural development, and synaptic plasticity. Calmodulin (CaM) regulates NMDARs by binding tightly to the C0 and C1 regions of their NR1 subunit. The conserved tryptophan is considered to be the anchor residue [1].

1: The NMDA receptor NR1 C1 region bound to calmodulin: structural insights into functional differences between homologous domains. Ataman ZA, Gakhar L, Sorensen BR, Hell JW, Shea MA; Structure. 2007;15:1603-1617. PMID:18073110