Mechanism of activity inversion for GluN2B-selective negative allosteric modulators.

N-methyl-D-aspartate receptors are ionotropic glutamate receptors that mediate the slow component of excitatory neurotransmission. Modulators of N-methyl-D-aspartate receptor function have long been evaluated as pharmacotherapies to treat neurological disorders such as Parkinson's disease, Alzheimer's disease, schizophrenia, stroke, and other neuropsychiatric and neurodegenerative disorders. We describe the mechanisms of action and explore the structural determinants underlying a phenomenon where GluN2B-specific negative allosteric modulators from the 93- and 96-series can be inverted to act as positive allosteric modulators by mutations at 2 GluN1 residues in their binding pocket located within the amino-terminal domain. Mutations at GluN1-Y109 that invert the activity could each conceivably strengthen the interaction between the residue and 93-31, resulting in a switch from enhancement to relief of tonic inhibition of the receptor by protons. The demonstration that this binding site is capable of being tuned for either inhibition or potentiation provides an opportunity to design novel positive allosteric modulators for potential therapeutic development in humans. SIGNIFICANCE STATEMENT: Mutations of 2 residues in the N-methyl-D-aspartate receptor GluN1 subunit amino-terminal domain independently interconvert GluN2B-selective negative allosteric modulators into positive allosteric modulators. This work provides a path for the discovery of the structural requirements for GluN2B-specific positive allosteric modulation.