Department of Chemistry, Grinnell College, Grinnell, Iowa, USA.
Mol Pharmacol. 2012 Feb;81(2):239-49. doi: 10.1124/mol.111.076059. Epub 2011 Nov 7.
We are interested in the allosteric modulation of neuronal nicotinic acetylcholine receptors (nAChRs). We have postulated that the anthelmintic morantel (Mor) positively modulates (potentiates) rat α3β2 receptors through a site located at the β(+)/α(-) interface that is homologous to the canonical agonist site (J Neurosci 29:8734-8742, 2009). On this basis, we aimed to determine the site specificity by studying differences in modulation between α3β2 and α4β2 receptors. We also compared modulation by Mor with that of the related compound oxantel (Oxa). Whereas Mor and Oxa each potentiated α3β2 receptors 2-fold at saturating acetylcholine (ACh) concentrations, Mor had no effect on α4β2 receptors, and Oxa inhibited ACh-evoked responses. The inhibition was noncompetitive, but not due to open channel block. Furthermore, the nature and extent of modulation did not depend on subunit stoichiometry. We studied six positions at the α(-) interface that differ between α3 and α4. Two positions (α3Ile57 and α3Thr115) help mediate the effects of the modulators but do not seem to contribute to specificity. Mutations in two others (α3Leu107 and α3Ile117) yielded receptors with appreciable α4-character; that is, Mor potentiation was reduced compared with wild-type α3β2 control and Oxa inhibition was evident. A fifth position (α3Glu113) was unique in that it discriminated between the two compounds, showing no change in Mor potentiation from control but substantial Oxa inhibition. Our work has implications for rational drug design for nicotinic receptors and sheds light on mechanisms of allosteric modulation in nAChRs, especially the subtle differences between potentiation and inhibition.
我们对神经元烟碱型乙酰胆碱受体（nAChRs）的别构调节很感兴趣。我们假设驱虫药莫仑特（Mor）通过位于β(+)/α(-)界面的一个与经典激动剂位点同源的位点正向调节（增强）大鼠α3β2 受体（J Neurosci 29:8734-8742, 2009）。在此基础上，我们旨在通过研究α3β2 和 α4β2 受体之间的调节差异来确定该位点的特异性。我们还比较了 Mor 与相关化合物奥沙托嗪（Oxa）的调节作用。虽然 Mor 和 Oxa 都在饱和乙酰胆碱（ACh）浓度下使α3β2 受体增强 2 倍，但 Mor 对 α4β2 受体没有影响，而 Oxa 抑制 ACh 诱发的反应。这种抑制是非竞争性的，但不是由于开放通道阻塞引起的。此外，调节的性质和程度不依赖于亚基计量关系。我们研究了在α(-)界面上的六个位置，这些位置在α3 和α4 之间不同。两个位置（α3Ile57 和 α3Thr115）有助于调节因子的作用，但似乎不贡献于特异性。另外两个位置（α3Leu107 和 α3Ile117）的突变产生了具有明显α4 特征的受体，即与野生型α3β2 对照相比，Mor 增强作用降低，而 Oxa 抑制作用明显。第五个位置（α3Glu113）是独特的，它区分了这两种化合物，Mor 增强作用与对照相比没有变化，但 Oxa 抑制作用显著。我们的工作对烟碱型受体的合理药物设计具有启示意义，并阐明了 nAChRs 别构调节的机制，特别是增强作用和抑制作用之间的细微差异。
