Gong Zhou, Zhang Xu, Liu Maili, Jin Changwen, Hu Yunfei
State Key Laboratory of Magnetic Resonance Spectroscopy and Imaging, National Center for Magnetic Resonance in Wuhan, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan 430071, China.
Beijing NMR Center, College of Chemistry and Molecular Engineering and Beijing National Laboratory for Molecular Sciences, Peking University, Beijing 100871, China.
Proc Natl Acad Sci U S A. 2025 Mar 11;122(10):e2418559122. doi: 10.1073/pnas.2418559122. Epub 2025 Mar 7.
Despite the growing number of G protein-coupled receptor (GPCR) structures being resolved, the dynamic process of how GPCRs transit from the inactive toward the active state remains unclear. In this study, comprehensive molecular dynamics simulations were performed to explore how ligand binding modulates the conformational dynamics of the M2 muscarinic acetylcholine receptor (M2R). We observed a sequential occurrence of structural changes in the inactive-to-active transition of M2R induced by a superagonist iperoxo, which includes the orthosteric binding site contraction, the TM6 opening into an intermediate conformation, and a further structural change toward full activation upon binding to G protein or a G protein mimetic nanobody. Two activation intermediates were identified, which show structural features different from those reported for apo-GPCRs. Moreover, our results suggest that stabilization of a specific W400 conformation and enhanced F396 dynamics are crucial for activation, whereas distinct side-chain rotamer equilibriums of Y206 in the cytoplasmic cavity are correlated with agonist efficacies. Our work provides atomic-level structural insights into the agonist-induced M2R activation pathway and highlights a mechanism by which ligand efficacy can be encoded and transduced in the form of aromatic ring dynamics.
尽管已解析出的G蛋白偶联受体（GPCR）结构数量不断增加，但GPCR从非活性状态转变为活性状态的动态过程仍不清楚。在本研究中，我们进行了全面的分子动力学模拟，以探索配体结合如何调节M2型毒蕈碱乙酰胆碱受体（M2R）的构象动力学。我们观察到，超激动剂iperoxo诱导M2R从非活性状态向活性状态转变时，结构变化依次发生，包括正构结合位点收缩、TM6向中间构象开放，以及在与G蛋白或G蛋白模拟纳米抗体结合后向完全激活的进一步结构变化。我们鉴定出了两种激活中间体，它们的结构特征与报道的无配体GPCR不同。此外，我们的结果表明，特定W400构象的稳定和F396动力学的增强对激活至关重要，而细胞质腔内Y206不同的侧链旋转异构体平衡与激动剂效力相关。我们的工作为激动剂诱导的M2R激活途径提供了原子水平的结构见解，并突出了一种机制，通过该机制，配体效力可以以芳香环动力学的形式进行编码和传导。
