Molecular determinants of proton-sensitive N-methyl-D-aspartate receptor gating.
Extracellular protons inhibit N-methyl-D-aspartate (NMDA) receptors with an IC50 value in the physiological pH range. To identify the molecular determinants of proton sensitivity, we used scanning mutagenesis of the NR1 subunit to search for residues that control proton inhibition of NMDA receptors. Homology modeling of the extracellular domains suggested that residues at which mutations perturbed pH sensitivity were localized in discrete regions. The majority of mutations that strongly affected proton sensitivity were clustered in the extracellular end of the second transmembrane domain (M3) and adjacent linker leading to the S2 portion of the glycine-binding domain of NR1. Mutations in NR2A confirmed that the analogous region controls the pH sensitivity of this subunit and also identified the linker region between the third transmembrane domain (M4) and the S2 portion of the NR2 glutamate binding domain as an additional determinant of proton sensitivity. One mutant receptor, NR1(A649C)/NR2A(A651T), showed a 145-fold reduction in the IC50 for protons (IC50, 17.3 microM corresponding to pH 4.9). The M3-S2 linker region has been suggested to control NMDA receptor gating, leading to the hypothesis that the proton sensor and receptor gate may be structurally and functionally integrated.
Low
Chian-Ming
CM
Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, 4301 W. Markham St., Little Rock, AR 77203-7199, USA.
Lyuboslavsky
Polina
P
French
Adam
A
Le
Phuong
P
Wyatte
Karen
K
Thiel
William H
WH
Marchan
Edward M
EM
Igarashi
Kazuei
K
Kashiwagi
Keiko
K
Gernert
Kim
K
Williams
Keith
K
Traynelis
Stephen F
SF
Zheng
Fang
F
D000595:Amino Acid Sequence; D000818:Animals; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D016202:N-Methylaspartate / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D011522:Protons; D016194:Receptors, N-Methyl-D-Aspartate / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis
D021122:Protein Subunits; D011522:Protons; D016194:Receptors, N-Methyl-D-Aspartate; D016202:N-Methylaspartate