Stoichiometry of a pore mutation that abolishes picrotoxin-mediated antagonism of the GABAA receptor.
Picrotoxin, a potent antagonist of the inhibitory central nervous system GABAA and glycine receptors, is believed to interact with residues that line the central ion pore. These pore-lining residues are in the second transmembrane domain (TM2) of each of the five constituent subunits. One of these amino acids, a threonine at the 6' location, when mutated to phenylalanine, abolishes picrotoxin sensitivity. It has been suggested that this threonine, via hydrogen bonding, directly interacts with the picrotoxin molecule. We previously demonstrated that this mutation, in the alpha, beta or gamma subunit, can impart picrotoxin resistance to the GABA receptor. Since the functional pentameric GABA receptor contains two alpha subunits, two beta subunits and one gamma subunit, it is not clear how many alpha and beta subunits must carry this mutation to impart the resistant phenotype. In this study, by coexpression of mutant alpha or beta subunits with their wild-type counterparts in various defined ratios, we demonstrate that any single subunit carrying the 6' mutation imparts picrotoxin resistance. Implications of this finding in terms of the mechanism of antagonism are considered.
Sedelnikova
Anna
A
Department of Physiology, UTHSCSA, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA.
Erkkila
Brian E
BE
Harris
Holly
H
Zakharkin
Stanislav O
SO
Weiss
David S
DS
D000818:Animals; D004305:Dose-Response Relationship, Drug; D018756:GABA Antagonists / Q000494:pharmacology*; D058787:GABA-A Receptor Antagonists; D008564:Membrane Potentials / Q000187:drug effects; D008845:Microinjections; D008958:Models, Molecular; D009154:Mutation; D017711:Nonlinear Dynamics; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000494:pharmacology*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011963:Receptors, GABA-A / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D014982:Xenopus laevis
D018756:GABA Antagonists; D058787:GABA-A Receptor Antagonists; D010852:Picrotoxin; D021122:Protein Subunits; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; C546242:Gabra1 protein, rat; C502185:Gabrb2 protein, rat; C546281:Gabrg2 protein, rat