Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory , 7000 East Avenue, Livermore, California 94550, United States.
Chem Res Toxicol. 2013 Oct 21;26(10):1444-54. doi: 10.1021/tx400167b. Epub 2013 Oct 2.
The type A GABA receptors (GABARs) are ligand-gated ion channels (LGICs) found in the brain and are the major inhibitory neurotransmitter receptors. Upon binding of an agonist, the GABAR opens and increases the intraneuronal concentration of chloride ions, thus hyperpolarizing the cell and inhibiting the transmission of the nerve action potential. GABARs also contain many other modulatory binding pockets that differ from the agonist-binding site. The composition of the GABAR subunits can alter the properties of these modulatory sites. Picrotoxin is a noncompetitive antagonist for LGICs, and by inhibiting GABAR, picrotoxin can cause overstimulation and induce convulsions. We use addition of picrotoxin to probe the characteristics and possible mechanism of an additional modulatory pocket located at the interface between the ligand-binding domain and the transmembrane domain of the GABAR. Picrotoxin is widely regarded as a pore-blocking agent that acts at the cytoplasmic end of the channel. However, there are also data to suggest that there may be an additional, secondary binding site for picrotoxin. Through homology modeling, molecular docking, and molecular dynamics simulations, we show that binding of picrotoxin to this interface pocket correlates with these data, and negative modulation occurs at the pocket via a kinking of the pore-lining helices into a more closed orientation.
A型 GABA 受体 (GABARs) 是存在于大脑中的配体门控离子通道 (LGICs)，是主要的抑制性神经递质受体。当与激动剂结合时，GABAR 打开并增加细胞内氯离子浓度，从而使细胞超极化并抑制神经动作电位的传递。GABAR 还包含许多其他调节性结合口袋，这些口袋与激动剂结合位点不同。GABAR 亚基的组成可以改变这些调节性结合位点的性质。苦杏仁酸是 LGICs 的非竞争性拮抗剂，通过抑制 GABAR，苦杏仁酸可以引起过度刺激并引发惊厥。我们使用添加苦杏仁酸来探测位于 GABAR 配体结合域和跨膜域界面的附加调节性口袋的特征和可能的机制。苦杏仁酸被广泛认为是一种位于通道胞质末端的孔阻断剂。然而，也有数据表明可能存在另一个次要的苦杏仁酸结合位点。通过同源建模、分子对接和分子动力学模拟，我们表明，苦杏仁酸与该界面口袋的结合与这些数据相关，并且通过将孔衬螺旋向内折叠成更封闭的取向，在口袋处发生负调节。
