Site-specific fluorescence reveals distinct structural changes with GABA receptor activation and antagonism.
Neurotransmitter-operated ion channels, such as the GABA (gamma-aminobutyric acid) receptor, are important in fast synaptic transmission between neurons. Using site-specific fluorescent labeling and simultaneous electrophysiological analysis in Xenopus laevis oocytes expressing recombinant rho1 GABA receptors, we identified agonist-mediated molecular rearrangements at three positions within and near the agonist-binding pocket that were highly correlated with receptor activation. We also show that competitive antagonists induced distinct rearrangements on their own that stabilized the receptor in a closed state. Finally, the allosteric antagonist picrotoxin induced a global conformational change that was sensed in the subunit-subunit interface of the amino (N)-terminal domain, distant from its presumed site of action within the transmembrane domains. This first detection in real time of molecular rearrangements of a ligand-activated receptor provides insights into the structural correlates of activation, antagonism and allosteric modulation.
D000494:Allosteric Regulation; D000818:Animals; D001667:Binding, Competitive / Q000502:physiology; D005260:Female; D005456:Fluorescent Dyes; D018756:GABA Antagonists / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D010852:Picrotoxin / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D018079:Receptors, GABA / Q000737:chemistry* / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry; D013329:Structure-Activity Relationship; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D005456:Fluorescent Dyes; D018756:GABA Antagonists; D010852:Picrotoxin; D018079:Receptors, GABA; D011994:Recombinant Proteins; D005680:gamma-Aminobutyric Acid