The pentameric γ-aminobutyric acid type A receptors (GABA_ARs) are the major inhibitory ligand-gated ion channels in the central nervous system. They mediate diverse physiological functions, mutations in them are associated with mental disorders and they are the target of many drugs such as general anesthetics, anxiolytics and anti–convulsants. The five subunits of synaptic GABA_ARs are arranged around a central pore in the order β-α-β-α-γ. In the outer third of the transmembrane domain (TMD) drugs may bind to five homologous intersubunit binding sites. Etomidate binds between the pair of β – α subunit interfaces (designated as β⁺/α^–) and R–mTFD-MPAB binds to an α⁺/β^– and an γ⁺/β^– subunit interface (a β^– selective ligand). Ligands that bind selectively to other homologous sites have not been characterized. We have synthesized a novel photolabel, (2,6-diisopropyl-4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenyl)methanol or pTFD-di-iPr-BnOH). It is a potent general anesthetic that positively modulates agonist and benzodiazepine binding. It enhances GABA–induced currents, shifting the GABA concentration-response curve to lower concentrations. Photolabeling–protection studies show that it has negligible affinity for the etomidate sites and high affinity for only one of the two R–mTFD-MPAB sites. Exploratory site–directed mutagenesis studies confirm the latter conclusions and hint that pTFD-di-iPr-BnOH may bind between the α⁺/β^– and α⁺/γ^– subunits in the TMD, making it an α⁺ ligand. The latter α⁺/γ^– site has not previously been implicated in ligand binding. Thus, pTFD-di-iPr-BnOH is a promising new photolabel that may open up a new pharmacology for synaptic GABA_ARs.

五聚体A型γ-氨基丁酸受体（GABA _A Rs）是中枢神经系统中主要的抑制配体门控离子通道。它们介导多种生理功能，其中的突变与精神障碍有关，并且它们是诸如全身麻醉药，抗焦虑药和抗惊厥药等许多药物的靶标。突触GABA _A Rs的五个亚基以β-α-β-α-γ的顺序排列在中心孔周围。在跨膜结构域（TMD）的外部三分之一中，药物可能会结合到五个同源的亚基结合位点。该对β之间依托咪酯结合- α亚基接口（命名为β ⁺ /α ^- ）和R-mTFD-MPAB结合到α ⁺ /β ^-和γ⁺ /β ^-亚单位界面（一个β ^-选择性配体）。尚未选择性结合其他同源位点的配体。我们已经合成了一种新型的光敏标签，（2,6-二异丙基-4-（3-（三氟甲基）-3H-二氮杂-3-基）苯基）甲醇或pTFD-di-iPr-BnOH。这是一种有效的全身麻醉剂，可积极调节激动剂和苯并二氮杂卓的结合。它增强了GABA诱导的电流，将GABA浓度-响应曲线移至较低浓度。光标记保护研究表明，它对依托咪酯位点的亲和力可忽略不计，对两个R–mTFD-MPAB位点中的仅一个具有高亲和力。探索性定点诱变研究证实了后者的结论，并暗示pTFD-di-iPr-BnOH可能在α ⁺之间结合/β ^-和α ⁺ /γ ^-在TMD亚基，使得它的α ⁺配体。后者α ⁺ /γ ^-网站已经先前未在配体结合牵连。因此，pTFD-di-iPr-BnOH是一种有前途的新光敏标签，可以为突触GABA _A Rs开辟新的药理学。