| UniProt ID | [Q13224](https://www.uniprot.org/uniprot/Q13224) |
| Molecular Weight | 166 kDa |
| Subcellular Localization | Plasma membrane, postsynaptic density |
| PDB Structures | 4PE5, 5FXG, 6MMQ |
| Gene | [GRIN2B](/entities/grin2b) |
NMDA receptor NR2B subunit, glutamate-binding modulatory subunit, regulates channel kinetics and synaptic localization.
The NMDA receptor subunit NR2B (GRIN2B gene product) is a modulatory subunit that combines with NR1 to form functional NMDA receptors. NR2B confers unique biophysical and pharmacological properties:
Structure and Assembly
- Large N-terminal domain with ifenprodil binding site (NR2B-selective antagonist)
- Glutamate-binding domain (distinct from NR1's glycine site)
- C-terminal domain with PDZ-binding motif for synaptic anchoring
- Forms heterotetramers: typically 2 NR1 + 2 NR2 subunits
Developmental Regulation
- Predominantly expressed early in development
- Gradual switch from NR2B to NR2A during maturation (synaptic pruning)
- NR2B-rich receptors mediate developmental plasticity
- Adult expression concentrated in forebrain, hippocampus, cortex
Biophysical Properties
- Longer channel open time compared to NR2A-containing receptors
- Higher affinity for glutamate (prolonged activation)
- Enhanced calcium influx per activation event
- Slower deactivation kinetics
Synaptic Function
- Critical for spine development and synaptic maturation
- Mediates long-term potentiation in hippocampus
- PSD-95 interaction via C-terminus anchors receptors at synapses
- Activity-dependent trafficking regulates surface expression
NR2B-containing NMDA receptors are particularly implicated in excitotoxic neurodegeneration:
Excitotoxicity Vulnerability
- NR2B-rich receptors generate larger calcium loads than NR2A-containing receptors
- Extrasynaptic NR2B receptors particularly linked to cell death signaling
- Prolonged glutamate exposure preferentially activates NR2B receptors
- Distinct downstream signaling: NR2B → calpain, mitochondrial dysfunction, cell death
Alzheimer's Disease
- Aβ oligomers increase surface expression of NR2B receptors
- Enhanced NR2B-dependent calcium influx contributes to synaptic loss
- NR2B-Fyn interaction promotes tau pathology
- NR2B antagonists show neuroprotection in AD models
- Memantine preferentially blocks overactive NR2B-containing receptors
Huntington's Disease
- Striatal NR2B upregulation observed in HD models
- Mutant huntingtin enhances NR2B surface expression
- NR2B-selective antagonists reduce striatal degeneration
- Enhanced sensitivity to quinolinic acid excitotoxicity
Stroke and Hypoxia-Ischemia
- NR2B-containing receptors mediate hypoxic neuronal death
- Ifenprodil (NR2B antagonist) reduces infarct size in animal models
- Clinical trials limited by side effects and therapeutic window
Epilepsy and Developmental Disorders
- GRIN2B mutations cause epileptic encephalopathy
- Gain-of-function variants: increased seizure susceptibility
- Loss-of-function: intellectual disability, autism features
- Some variants respond to memantine or ketamine
NR2B-selective targeting offers potential advantages in neurodegeneration:
NR2B-Selective Antagonists
- Ifenprodil: Prototypical NR2B antagonist; binds allosteric site on N-terminal domain
- Traxoprodil (CP-101,606): Investigated for stroke and depression
- EVT-101: Phase II trials for depression and neuropathic pain
- Radiprodil: Under investigation for developmental disorders with GRIN2B gain-of-function
Clinical Experience
- NR2B antagonists generally well-tolerated compared to non-selective NMDA antagonists
- Less impairment of synaptic plasticity than channel blockers
- Potential applications in HD, PD dyskinesia, stroke, depression
- Therapeutic window still narrow for acute neuroprotection
Emerging Strategies
- Activity-dependent blockers: Enhanced inhibition during sustained activation
- Bi-functional compounds: NR2B antagonist + additional neuroprotective mechanism
- Gene therapy: Antisense oligonucleotides targeting NR2B
- Combination therapy: NR2B antagonists + antioxidants or anti-inflammatory agents