Alterations of the benzodiazepine site of rat alpha 6 beta 2 gamma 2-GABAA receptor by replacement of several divergent amino-terminal regions with the alpha 1 counterparts.
1. The benzodiazepine site of the alpha 6 beta 2 gamma 2 subtype of gamma-aminobutyric acidA (GABAA) receptors is distinguishable from that of the alpha 1 beta 2 gamma 2 subtype by its inability to interact with classical benzodiazepines (i.e., diazepam) and its agonistic response to Ro 15-1788, which behaves as an antagonist in the alpha 1 beta 2 gamma 2 subtype. 2. The point mutation of Arg 100 of the alpha 6 subunit to histidine (the corresponding residue in alpha 1) has been shown to enable the alpha 6 beta 2 gamma 2 subtype to interact with diazepam but failed in this study to abolish the ability of Ro 15-1788 to enhance GABA-induced Cl- currents. 3. Here we identified the segment of P161 to L187 of alpha 6 to contain the functional region responsible for the agonistic action of Ro 15-1788. Its replacement with the corresponding alpha 1 sequence abolished the ability of Ro 15-1788 to enhance GABA currents without appreciable effects on its binding affinity to the benzodiazepine site or on the functionality of the other benzodiazepine site ligands such as diazepam, U-92330 and 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate. These data support the evidence that the functionality of a given ligand could arise from a single region of the benzodiazepine site, not shared by others. 4. In addition we have learned that several residues in the N-terminal region of alpha 6, such as R100, V142 and N143, have the ability to influence GABA-dependent Cl- current induction probably by allosterically modulating low affinity GABA sites.
Im
W B
WB
Pharmacia & Upjohn, INC. Kalamazoo, Michigan 49001, USA.
Pregenzer
J F
JF
Binder
J A
JA
Alberts
G L
GL
Im
H K
HK
D000595:Amino Acid Sequence; D000818:Animals; D001569:Benzodiazepines / Q000378:metabolism* / Q000494:pharmacology; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D018118:Chloride Channels / Q000187:drug effects; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques; D051381:Rats; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018118:Chloride Channels; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D005680:gamma-Aminobutyric Acid