The human NMDA receptor GluN2A^N615K variant influences channel blocker potency

N-methyl-D-aspartate (NMDA) receptors are glutamate receptors with key roles in synaptic plasticity, due in part to their Mg²⁺ mediated voltage-dependence. A large number of genetic variants affecting NMDA receptor subunits have been found in people with a range of neurodevelopmental disorders, including GluN2A^N615K (GRIN2A^C1845A) in two unrelated individuals with severe epileptic encephalopathy. This missense variant substitutes a lysine in place of an asparagine known to be important for blockade by Mg²⁺ and other small molecule channel blockers. We therefore measured the impact of GluN2A^N615K on a range of NMDA receptor channel blockers using two-electrode voltage clamp recordings made in Xenopus oocytes. We found that GluN2A^N615K resulted in block by Mg²⁺ 1 mmol/L being greatly reduced (89% vs 8%), block by memantine 10 micromol/L (76% vs 27%) and amantadine 100 micromol/L (45% vs 17%) being substantially reduced, block by ketamine 10 micromol/L being modestly reduced (79% vs 73%) and block by dextromethorphan 10 micromol/L being enhanced (45% vs 55%). Coapplying Mg²⁺ with memantine or amantadine did not reduce the GluN2A^N615K block seen with either small molecule. In addition, we measured single-channel conductance of GluN2A^N615K-containing NMDA receptors in outside-out patches pulled from Xenopus oocytes, finding a 4-fold reduction in conductance (58 vs 15 pS). In conclusion, the GluN2A^N615K variant is associated with substantial changes to important physiological and pharmacological properties of the NMDA receptor. Our findings are consistent with GluN2A^N615K having a disease-causing role, and inform potential therapeutic strategies.