GAMMA-AMINOBUTYRIC-ACID TYPE-A RECEPTOR POINT MUTATION INCREASES THE AFFINITY OF COMPOUNDS FOR THE BENZODIAZEPINE SITE

Recombinantly expressed gamma-aminobutyric acid type A (GABA(A)) receptors consisting of alpha-1, beta-2, and gamma-2-subunits contain a binding site for benzodiazepines that differs in its properties from that of alpha-3-beta-2-gamma-2-receptors. Amino acid substitutions between the GABA(A) receptor alpha-subunits were analyzed for their effect on the binding of compounds to the benzodiazepine site. By converting ever smaller regions of the alpha-3-subunit sequence to that of the alpha-1-subunit, we show that a single substitution (glycine for glutamic acid) increases the affinity for several compounds approximately 10-fold without changing the affinity for nonselective compounds. Hence, the identified amino acids may interact directly with the ligand and define part of the benzodiazepine binding sites in these receptors.