Crystal structure of the GluA2o LBD in complex with glutamate and HBT1

influx assay in primary neurons and, from a chemical library, discovered two AMPA-R potentiators with lower agonistic effects: 2-(((5-methyl-3-(trifluoromethyl)-1H-pyrazol-1-yl)acetyl)amino)-4,5,6,7-tetrahydro-1-benzothiophene-3-carboxamide (HBT1) and (3S)-1-(4-tert-butylphenyl)-N-((1R)-2-(dimethylamino)-1-phenylethyl)-3-isobutyl-2-oxopyrrolidine-3-carboxamide (OXP1). In a patch-clamp study using primary neurons, HBT1 showed little agonistic effect, whereas both LY451395 and OXP1 showed remarkable agonistic effects. HBT1, but not OXP1, did not show remarkable bell-shaped response in BDNF production in primary neurons. HBT1 bound to the ligand-binding domain (LBD) of AMPA-R in a glutamate-dependent manner. The mode of HBT1 and LY451395 binding to a pocket in the LBD of AMPA-R differed: HBT1, but not LY451395, formed hydrogen bonds with S518 in the LBD. OXP1 may bind to a cryptic binding pocket on AMPA-R. Lower agonistic profile of HBT1 may associate with its lower risks of bell-shaped responses in BDNF production in primary neurons.