Role of histidyl residues in the binding of ligands to the porcine N-methyl-D-aspartate receptor.

Possible involvement of histidyl residues in the binding of ligands to ionotropic glutamate receptors and to modulatory sites on the N-methyl-D-aspartate (NMDA) receptor was assessed in porcine cortical synaptic plasma membranes after covalent modification with diethyl pyrocarbonate (DEPC). Binding of [3H]glutamate to the NMDA sites was enhanced but to the 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and kainate receptors unaffected by 1 and 5 mM DEPC. Binding of 3-[(R)-carboxypiperazin-4-yl]-[1,2-(3)H]propyl-1-phosphonate ([3H]CPP) was reduced in a dose-dependent manner by DEPC and the activation of binding by 1-hydroxy-3-amino-2-pyrrolidone (HA-966) blocked by 10 mM DEPC. DEPC reduced the strychnine-insensitive binding of [3H]glycine and the glycine- and glutamate-activated binding of [3H]dizocilpine. Protection experiments indicated that histidyl residues are directly involved in the binding of glycine (but not HA-966) and allosterically modulate the binding of glutamate, CPP and dizocilpine. The results corroborate the existence of agonist- and antagonist-preferring sites or conformational states of the NMDA receptors.