Identification and mechanism of action of two histidine residues underlying high-affinity Zn2+ inhibition of the NMDA receptor.
Zinc (Zn2+) inhibition of N-methyl-D-aspartate receptor (NMDAR) activity involves both voltage-independent and voltage-dependent components. Recombinant NR1/NR2A and NR1/NR2B receptors exhibit similar voltage-dependent block, but voltage-independent Zn2+ inhibition occurs with much higher affinity for NR1/NR2A than NR1/NR2B receptors (nanomolar versus micromolar IC50, respectively). Here, we show that two neighboring histidine residues on NR2A represent the critical determinant (termed the "short spacer") for high-affinity, voltage-independent Zn2+ inhibition using the Xenopus oocyte expression system and site-directed mutagenesis. Mutation of either one of these two histidine residues (H42 and H44) in the extracellular N-terminal domain of NR2A shifted the IC50 for high-affinity Zn2+ inhibition approximately 200-fold without affecting the EC50 of the coagonists NMDA and glycine. We suggest that the mechanism of high-affinity Zn2+ inhibition on the NMDAR involves enhancement of proton inhibition.
Choi
Y B
YB
Cerebrovascular and NeuroScience Research Institute, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Lipton
S A
SA
D000818:Animals; D004047:Diethyl Pyrocarbonate / Q000494:pharmacology; D005260:Female; D006639:Histidine / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D009154:Mutation / Q000502:physiology; D009865:Oocytes; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms / Q000037:antagonists & inhibitors; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014982:Xenopus laevis; D015032:Zinc / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D020033:Protein Isoforms; D016194:Receptors, N-Methyl-D-Aspartate; D006639:Histidine; D015032:Zinc; D004047:Diethyl Pyrocarbonate