IDENTIFICATION OF AMINO-ACIDS IN THE N-METHYL-D-ASPARTATE RECEPTOR NR1 SUBUNIT THAT CONTRIBUTE TO THE GLYCINE BINDING-SITE

The mammalian N-methyl-D-aspartate (NMDA) receptor complex is thought to consist of an NR1 subunit in combination with one or more of the fo ur NR2 subunits (A, B, C, and D). When corresponding cDNAs are express ed in Xenopus oocytes, ion channels with the characteristic profile of NMDA receptors are formed. The receptor is unique in requiring two co agonists, glutamate and glycine, for activation of the channel. We hav e used site-directed mutagenesis to study amino acids in the human NR1 subunit that contribute to the glycine binding site of the NMDA recep tor without affecting the agonist site for glutamate. Mutations to D48 1 and K483 produced receptors with up to 160-fold lower affinities for glycine, as well as other agonists and partial agonists, without affe cting maximum current size or the degree of agonist efficacy, The D481 A mutation also led to 40-50-fold lower affinities for two structurall y diverse glycine site antagonists. From these data we propose that th e carboxyl group of this aspartate interacts with the amino moiety of glycine and the equivalent group contained in other agonists and antag onists.