Megan M. Eaton, Allison L. Germann, Ruby Arora, Lily Q. Cao, Xiaoyi Gao, Daniel J. Shin, Albert Wu, David C. Chiara, Jonathan B. Cohen, Joe Henry Steinbach, Alex S. Evers and Gustav Akk Pages 772 - 780 ( 9 )
Background: Propofol is a sedative agent that at clinical concentrations acts by allosterically activating or potentiating the γ-aminobutyric acid type A (GABAA) receptor. Mutational, modeling, and photolabeling studies with propofol and its analogues have identified potential interaction sites in the transmembrane domain of the receptor. At the "+" of the β subunit, in the β-α interface, meta-azipropofol labels the M286 residue in the third transmembrane domain. Substitution of this residue with tryptophan results in loss of potentiation by propofol. At the "-" side of the β subunit, in the α-β interface (or β-β interface, in the case of homomeric β receptors), ortho-propofol diazirine labels the H267 residue in the second transmembrane domain. Structural modeling indicates that the β(H267) residue lines a cavity that docks propofol with favorable interaction energy.
Method: We used two-electrode voltage clamp to determine the functional effects of mutations to the "+" and "-" sides of the β subunit on activation of the α1β3 GABAA receptor by propofol.
Results: We found that while the individual mutations had a small effect, the combination of the M286W mutation with tryptophan mutations of selected residues at the α-β interface leads to strong reduction in gating efficacy for propofol.
Conclusion: We conclude that α1β3 GABAA receptors can be activated by propofol interactions with the β-β, α-β, and β-α interfaces, where distinct, non-equivalent regions control channel gating. Any interface can mediate activation, hence substitutions at all interfaces are required for loss of activation by propofol.
Activation, binding site, GABAA receptor, mutation, propofol, structure.
Department of Anesthesiology, Washington University, Campus Box 8054, 660 South Euclid Ave, St. Louis, MO 63110.