Amino acid residue 200 on the α1 subunit of GABAA receptors affects the interaction with selected benzodiazepine binding site ligands

Mutant alpha(1) subunits of the GABA(A) receptor were coexpressed in combination with the wild-type beta(2) and gamma(2) subunits in human embryonic kidney (HEK) 293 cells. The binding properties of various benzodiazepine site ligands were determined by displacement of ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5a]-[1,4]benzodiazepine-3-carboxylate ([H-3]Ro 15-1788). The mutation G200E led to a decrease in zolpidem and 3-methyl-6-[3-(trifluoromethyl)phenyl]- 1,2,4-triazolo[4,3-b]pyridazine (CL 218872) affinity amounting to 16- and 8-fold. Receptors containing a conservative T206V substitution showed a 41- and 38-fold increase in methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) and CL 218872 affinity combined with a decrease in diazepam and zolpidem affinity, amounting to 7- and 10-fold. Two mutations, Q203A and Q203S showed almost no effects on the binding of benzodiazepine site ligands, indicating that this residue is not involved in the binding of benzodiazepines and related compounds. (C) 1998 Elsevier Science B.V. All rights reserved.