Saleh Noureldin, Saladino Giorgio, Gervasio Francesco Luigi, Clark Timothy
Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials , Friedrich-Alexander-Universität Erlangen-Nürnberg , Nägelsbachstraße 25 , 91052 Erlangen , Germany . Email:
Department of Chemistry , University College London , London WC1H 0AJ , UK.
Chem Sci. 2017 May 1;8(5):4019-4026. doi: 10.1039/c6sc04647a. Epub 2017 Mar 24.
Signalling by G-protein coupled receptors usually occurs ternary complexes formed under cooperative binding between the receptor, a ligand and an intracellular binding partner (a G-protein or β-arrestin). While a global rational for allosteric effects in ternary complexes would be of great help in designing ligands with specific effects, the paucity of structural data for ternary complexes with β-arrestin, together with the intrinsic difficulty of characterizing the dynamics involved in the allosteric coupling, have hindered the efforts to devise such a model. Here we have used enhanced-sampling atomistic molecular-dynamics simulations to investigate the dynamics and complex formation mechanisms of both β-arrestin- and G-complexes with the β2-adrenergic receptor (ADRB2) in its apo-form and in the presence of four small ligands that exert different allosteric effects. Our results suggest that the structure and dynamics of arrestin-ADRB2 complexes depend strongly on the nature of the small ligands. The complexes exhibit a variety of different coupling orientations in terms of the depth of the finger loop in the receptor and activation states of ADRB2. The simulations also allow us to characterize the cooperativity between the ligand and intracellular binding partner (IBP). Based on the complete and consistent results, we propose an experimentally testable extended ternary complex model, where direction of the cooperative effect between ligand and IBP (positive or negative) and its magnitude are predicted to be a characteristic of the ligand signaling bias. This paves the avenue to the rational design of ligands with specific functional effects.
G蛋白偶联受体的信号传导通常发生在受体、配体和细胞内结合伴侣（G蛋白或β-抑制蛋白）之间通过协同结合形成的三元复合物中。虽然三元复合物变构效应的整体原理对设计具有特定效应的配体有很大帮助，但β-抑制蛋白三元复合物的结构数据匮乏，加上表征变构偶联中涉及的动力学存在内在困难，阻碍了构建此类模型的努力。在此，我们使用增强采样原子分子动力学模拟，研究了β2-肾上腺素能受体（ADRB2）在无配体状态以及存在四种具有不同变构效应的小配体时，与β-抑制蛋白和G蛋白复合物的动力学及复合物形成机制。我们的结果表明，抑制蛋白-ADRB2复合物的结构和动力学强烈依赖于小配体的性质。就受体中手指环的深度和ADRB2的激活状态而言，这些复合物呈现出多种不同的偶联取向。模拟还使我们能够表征配体与细胞内结合伴侣（IBP）之间的协同作用。基于完整且一致的结果，我们提出了一个可通过实验验证的扩展三元复合物模型，其中配体与IBP之间协同效应的方向（正向或负向）及其大小预计是配体信号偏向的一个特征。这为合理设计具有特定功能效应的配体铺平了道路。
