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-methy l-D-aspartate (NMDA) receptor was assessed in porcine cortical synapti c plasma membranes after covalent modification with diethyl pyrocarbon ate (DEPC). Binding of [H-3]glutamate to the NMDA sites was enhanced b ut to the 2-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) and kainate receptors unaffected by 1 and 5 mM DEPC. Binding of rboxypipe razin-4-yl]-[1,2-H-3]propyl-1-phosphonate ([H-3]CPP) was reduced in a dose-dependent manner by DEPC and the activation of binding by 1-hydro xy-3-amino-2-pyrrolidone (HA-966) blocked by 10 mM DEPC. DEPC reduced the strychnine-insensitive binding of [H-3]glycine and the glycine- an d glutamate-activated binding of [H-3]dizocilpine. Protection experime nts indicated that histidyl residues are directly involved in the bind ing of glycine (but not HA-966) and allosterically modulate the bindin g of glutamate, CPP and dizocilpine. The results corroborate the exist ence of agonist- and antagonist-preferring sites or conformational sta tes of the NMDA receptors. (C) 1997 Elsevier Science Ireland Ltd.