The Journal of Neuroscience, December 1, 2002, 22(23):10209-10216
DRPEER: A Motif in the Extracellular Vestibule Conferring High
Ca2+ Flux Rates in NMDA Receptor Channels
Junryo
Watanabe2,
Christine
Beck3,
Thomas
Kuner3, 4,
Louis S.
Premkumar5, and
Lonnie P.
Wollmuth1
1 Department of Neurobiology and Behavior and
2 Graduate Program in Neurobiology and Behavior, State
University of New York at Stony Brook, Stony Brook, New York
11794-5230, 3 Abteilung Molekulare Neurobiologie and
4 Zellphysiologie, Max-Planck-Institut für
medizinische Forschung, D-69120 Heidelberg, Germany, and
5 Department of Pharmacology, Southern Illinois University
School of Medicine, Springfield, Illinois 62702
The high flux rate of Ca2+ through NMDA receptor
(NMDAR) channels is critical for their biological function and may
depend on a Ca2+ binding site in the extracellular
vestibule. We screened substitutions of hydrophilic residues exposed in
the vestibule and identified a cluster of charged residues and a
proline, the DRPEER motif, positioned C terminal to M3, that is unique
to the NR1 subunit. Charge neutralization or conversion of residues in
DRPEER altered fractional Ca2+ currents in a manner
consistent with its forming a binding site for Ca2+.
Similarly, in a mutant channel in which all of the negative charges are
neutralized (ARPAAR), the block by extracellular
Ca2+ of single-channel current amplitudes is
attenuated. In these same channels, the block by extracellular
Mg2+ is unaffected. DRPEER is located
extracellularly, and its contribution to Ca2+ influx
is distinct from that of the narrow constriction. We conclude that key
residues in DRPEER, acting as an external binding site for
Ca2+, along with a conserved asparagine in the M3
segment proper, contribute to the high fractional
Ca2+ currents in these channels under physiological
conditions. Therefore, these domains represent critical molecular
determinants of NMDAR function in synaptic physiology.
Key words:
glutamate receptor; fractional Ca2+
currents; Ca2+ permeability; extracellular
vestibule; synaptic physiology; Ca2+ binding
site
Copyright © 2002 Society for Neuroscience 0270-6474/02/222310209-08$05.00/0
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