Intracellular domains of NR2 alter calcium-dependent inactivation of N-methyl-D-aspartate receptors.
At central excitatory synapses, the transient elevation of intracellular calcium reduces N-methyl-D-aspartate (NMDA) receptor activity. Such 'calcium-dependent inactivation' is mediated by interactions of calcium/calmodulin and alpha-actinin with the C terminus of NMDA receptor 1 (NR1) subunit. However, inactivation is also NR2-subunit specific, because it occurs in NR2A- but not NR2C-containing receptors. We examined the molecular basis for NR2-subunit specificity using chimeric and mutated NMDA receptor subunits expressed in HEK293 cells. We report that the intracellular loop immediately distal to the pore-forming P-loop M2 (M2-3 loop), as well as a short region in the C terminus, are involved in NR2-subunit specificity. Within the M2-3 loop, substitution of residue 619 in NR2A (valine) for the corresponding NR2C residue (isoleucine) reduced inactivation without affecting calcium permeability of the channel. In contrast, a Q620E mutation in NR2A reduced the relative calcium permeability without altering inactivation. Mutation of three serine/threonine residues in the M2-3 loop also reduced inactivation, as did substitution of the intracellular C terminus of NR2A for NR2C. We speculate that the M2-3 loop of NR2 modulates calcium-dependent inactivation by interacting with the NR1 C terminus, a region known to be essential for inactivation.
Vissel
Bryce
B
Molecular Neurobiology Laboratory, the Salk Institute, La Jolla, California, USA.
Krupp
Johannes J
JJ
Heinemann
Stephen F
SF
Westbrook
Gary L
GL
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004594:Electrophysiology; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000235:genetics; D009435:Synaptic Transmission
C120997:NR2A NMDA receptor; D021122:Protein Subunits; D016194:Receptors, N-Methyl-D-Aspartate; D012694:Serine; D002118:Calcium