GABA_A receptor interactions with propofol: Binding site location and conformational changes

The GABA_A receptor is a major target of the intravenous anesthetic propofol. In order to obtain an understanding of propofol's actions at a molecular level we have attempted to identify the propofol binding site and the conformational changes that propofol binding induces. Using changes in the reactivity of cysteines substituted in the M3 membrane-spanning segment we show that propofol stabilizes a receptor conformational state that is distinct from the states stabilized by GABA and by diazepam. Separately, we have used propofol's ability to protect engineered cysteines from modification by the sulfhydryl-reactive reagent, pCMBS^-, to identify propofol binding site residues. β₂Met286, near the M3 extracellular end, is protected but the aligned residue α₁Ala291 and the M2 15′ residues are not. We infer that β₂Met286 is part of a propofol binding site. These studies are beginning to provide a molecular level description of general anesthetic action on GABA_A receptors.