Schematic representation of the super-active GluN1-E698C/GluN2B-L795C receptor locked in the "rolled" conformation, showing the NTD binding sites for spermine, zinc and ifenprodil, positive (+) and negative (-) allosteric modulators, respectively. Open circles indicate that the binding site is on the other side of the GluN2B NTD. The allosteric inhibitor H+ is also indicated, although its binding site remains i 