Yb. Choi et Sa. Lipton, Identification and mechanism of action of two histidine residues underlying high-affinity Zn2+ inhibition of the NMDA receptor, NEURON, 23(1), 1999, pp. 171-180
Zinc (Zn2+) inhibition of N-methyl-D-aspartate receptor (NMDAR) activity in
volves both voltage-independent and voltage-dependent components. Recombina
nt NR1/NR2A and NR1/NR2B receptors exhibit similar voltage-dependent block,
but voltage-independent Zn2+ inhibition occurs with much higher affinity f
or NR1/NR2A than NR1/NR2B receptors (nanomolar versus micromolar IC50, resp
ectively). Here, we show that two neighboring histidine residues on NR2A re
present the critical determinant (termed the "short spacer") for high-affin
ity, voltage-independent Zn2+ inhibition using the Xenopus oocyte expressio
n 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 similar to 200-fol
d 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.