The muscarinic M₂ acetylcholine receptor, one of the few G-protein coupled receptors that has not only been crystallized in both active and inactive conformations but also in the presence of a positive allosteric modulator, is an interesting system to study the molecular mechanisms of GPCR activation and ligand allosterism. Here, we have employed molecular dynamics (MD) simulations (adding to 14 μs in total) to study conformational changes triggered by the inverse agonist R-(−)-3-quinuclidinyl-benzilate (QNB) in the structure of the active M₂ receptor (PBD ID 4MQS) after replacement of the agonist iperoxo by the inverse agonist QNB. This permitted us to identify the sequence of events in the deactivation mechanism of the M₂ acetylcholine receptor, which results first in the rearrangement of the transmission switch, the subsequent opening of the extracellular portion of the receptor and finally, the closure of the intracellular part. We also evaluate the effect of the positive allosteric modulator LY2119620 when bound simultaneously with the orthosteric agonist iperoxo and find that it restricts the conformation of Trp422^7.35 in a position that modulates the orientation of the Tyr426^7.39 at the orthosteric-binding pocket.

中文翻译：

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M ₂毒蕈碱型乙酰胆碱受体的配体触发结构变化

毒蕈碱M ₂乙酰胆碱受体是少数几个G蛋白偶联受体，不仅在有活性和无活性构象中均已结晶，而且在正构构调节剂的存在下结晶，是研究GPCR分子机制的有趣系统。激活和配体变构。在这里，我们采用了分子动力学（MD）模拟（总共加起来为14μs）来研究由反向激动剂R -（-）-3-奎宁环基-苯甲酸酯（QNB）在活性M ₂的结构中触发的构象变化。反向激动剂QNB代替激动剂哌酮类药物（PBD ID 4MQS）。这使我们能够确定M ₂停用机制中的事件顺序乙酰胆碱受体，其首先导致传输开关的重排，随后受体的胞外部分打开，最后导致细胞内部分闭合。我们还评估了正构构调节剂LY2119620与正构激动剂iperoxo同时结合的效果，发现它在调节正构结合口袋中Tyr426 ^7.39方向的位置上限制了Trp422 ^7.35的构象。