This study examines how site-specific binding to three identified neurosteroid-binding sites in the α1β3 GABAA receptor (GABAAR) contributes to neurosteroid allosteric modulation. We found that the potentiating neurosteroid, allopregnanolone, but not its inhibitory 3β-epimer epi-allopregnanolone, binds to the canonical β3(+)–α1(-) intersubunit site that mediates receptor activation by neurosteroids. In contrast, both allopregnanolone and epi-allopregnanolone bind to intrasubunit sites in the β3 subunit, promoting receptor desensitization and the α1 subunit promoting effects that vary between neurosteroids. Two neurosteroid analogues with diazirine moieties replacing the 3-hydroxyl (KK148 and KK150) bind to all three sites, but do not potentiate GABAAR currents. KK148 is a desensitizing agent, whereas KK150 is devoid of allosteric activity. These compounds provide potential chemical scaffolds for neurosteroid antagonists. Collectively, these data show that differential occupancy and efficacy at three discrete neurosteroid-binding sites determine whether a neurosteroid has potentiating, inhibitory, or competitive antagonist activity on GABAARs.

中文翻译：

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神经类固醇对 GABAA 受体活化和脱敏的位点特异性作用

本研究探讨了与 α1β3 GABAA 受体 (GABAAR) 中三个已确定的神经类固醇结合位点的位点特异性结合如何促进神经类固醇变构调节。我们发现增强神经类固醇，别孕酮，但不是它的抑制性 3β-差向异构体表异孕酮，与介导神经类固醇激活受体的典型 β3(+)–α1(-) 亚基间位点结合。相比之下，别孕酮和表异孕酮都与 β3 亚基中的亚基内位点结合，促进受体脱敏和 α1 亚基促进作用，这些作用因神经类固醇而异。具有取代 3-羟基的二氮丙啶部分的两种神经类固醇类似物（KK148 和 KK1​​50）与所有三个位点结合，但不会增强 GABAAR 电流。KK148 是一种脱敏剂，而 KK150 没有变构活性。这些化合物为神经类固醇拮抗剂提供了潜在的化学支架。总的来说，这些数据表明，三个离散的神经类固醇结合位点的不同占有率和功效决定了一种神经类固醇是否对 GABAAR 具有增强、抑制或竞争性拮抗剂活性。