School of Life Sciences, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju, Korea.
Mol Pharmacol. 2012 Aug;82(2):143-55. doi: 10.1124/mol.112.078097. Epub 2012 Apr 30.
As previously reported, the activity of the large-conductance calcium (Ca(2+))-activated potassium (K(+)) (BK(Ca)) channel is strongly potentiated from the extracellular side of the cell membrane by certain benzofuroindole derivatives. Here, the mechanism of action of one of the most potent activators, 4-chloro-7-(trifluoromethyl)-10H-benzofuro[3,2-b]indole-1-carboxylic acid (CTBIC), is characterized. This compound, Compound 22 in the previous report (Chembiochem 6:1745-1748, 2005), potentiated the activity of the channel by shifting its conductance-voltage relationship toward the more negative direction. Cotreatment with CTBIC reduced the affinity of charybdotoxin, a peptide pore-blocker, whereas that of tetraethylammonium, a small pore-blocking quaternary ammonium, was not significantly altered. Guided by these results, scanning mutagenesis of the outer vestibule of the BK(Ca) channel was launched to uncover the molecular determinants that affect CTBIC binding. Alanine substitution of several amino acid residues in the turret region and the S6 helix of the channel decreased potentiation by CTBIC. Homology modeling and molecular dynamics simulation showed that some of these residues formed a CTBIC binding pocket between two adjacent α-subunits in the outer vestibule of the channel. Thus, it can be envisioned that benzofuroindole derivatives stabilize the open conformation of the channel by binding to the residues clustered across the extracellular part of the subunit interface. The present results indicate that the interface between different α-subunits of the BK(Ca) channel may play a critical role in the modulation of channel activity. Therefore, this interface represents a potential therapeutic target site for the regulation of K(+) channels.
如前所述，某些苯并呋喃吲哚衍生物从细胞膜的细胞外侧面强烈增强大电导钙（Ca(2+))激活钾（K(+)) (BK(Ca))) 通道的活性。在此，描述了最有效的激活剂之一 4-氯-7-(三氟甲基）-10H-苯并呋喃[3,2-b]吲哚-1-羧酸（CTBIC）的作用机制。这种化合物，前一份报告中的化合物 22（Chembiochem 6:1745-1748, 2005），通过将其电导-电压关系移向更负的方向来增强通道的活性。与 CTBIC 共同处理可降低沙雷毒素（一种肽孔阻断剂）的亲和力，而对四乙铵（一种小的孔阻塞季铵盐）的亲和力则没有明显改变。基于这些结果，对 BK(Ca) 通道外腔的扫描诱变展开，以揭示影响 CTBIC 结合的分子决定因素。通道的炮塔区域和 S6 螺旋中的几个氨基酸残基的丙氨酸取代降低了 CTBIC 的增强作用。同源建模和分子动力学模拟表明，这些残基中的一些在通道外腔的两个相邻α-亚基之间形成了一个 CTBIC 结合口袋。因此，可以设想苯并呋喃吲哚衍生物通过与亚基界面胞外部分上聚集的残基结合来稳定通道的开放构象。目前的结果表明，BK(Ca) 通道不同α-亚基之间的界面可能在调节通道活性中起关键作用。因此，该界面代表了调节 K(+) 通道的潜在治疗靶位。
