Ligand Binding Ensembles Determine Graded Agonist Efficacies at a G Protein-coupled Receptor
Ligand Binding Ensembles Determine Graded Agonist Efficacies at a G Protein-coupled Receptor
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DOI：
10.1074/jbc.m116.735431
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发表时间：
2016-07-29
影响因子：
4.8
通讯作者：
Mohr, Klaus
中科院分区：
文献类型：
--
作者：
Bock, Andreas;Bermudez, Marcel;Mohr, Klaus
G蛋白偶联受体是最大的膜受体家族，几乎调节人体的所有生理过程。激动剂与G蛋白偶联受体的结合诱导从非活性到活性受体构象的转变。受体动态平衡的生物物理学研究表明，即使在饱和浓度的激动剂和G蛋白模拟物存在下，一部分受体也可以保持在非活性状态。然而，激动剂结合的非活性受体的分子细节知之甚少。在这里，我们使用的模型，双体的正构/变构（即双构）激动剂的毒蕈碱M-2受体，以证明这种非活性激动剂受体复合物的存在和功能的分子水平。使用全原子分子动力学模拟，dynophores（即静态三维药效团和分子动力学为基础的构象采样的组合），配体设计，和受体诱变，我们表明，非活性激动剂。受体复合物可以从激动剂单独结合到变构前庭，而双构结合模式产生活性受体。每种激动剂形成不同的配体结合系综，并且不同的激动剂功效取决于纯变构（即无活性）与双变构（即活性）结合模式的比例。我们认为，这一概念可以解释激动剂-受体复合物为什么可以是无活性的，并且采用多种结合模式也可以推广到小激动剂，其中结合模式将仅细微不同并且仅限于一个结合位点。
G protein-coupled receptors constitute the largest family of membrane receptors and modulate almost every physiological process in humans. Binding of agonists to G protein-coupled receptors induces a shift from inactive to active receptor conformations. Biophysical studies of the dynamic equilibrium of receptors suggest that a portion of receptors can remain in inactive states even in the presence of saturating concentrations of agonist and G protein mimetic. However, the molecular details of agonist-bound inactive receptors are poorly understood. Here we use the model of bitopic orthosteric/allosteric (i.e. dualsteric) agonists for muscarinic M-2 receptors to demonstrate the existence and function of such inactive agonist.receptor complexes on a molecular level. Using all-atom molecular dynamics simulations, dynophores (i.e. a combination of static three-dimensional pharmacophores and molecular dynamics-based conformational sampling), ligand design, and receptor mutagenesis, we show that inactive agonist.receptor complexes can result from agonist binding to the allosteric vestibule alone, whereas the dualsteric binding mode produces active receptors. Each agonist forms a distinct ligand binding ensemble, and different agonist efficacies depend on the fraction of purely allosteric (i.e. inactive) versus dualsteric (i.e. active) binding modes. We propose that this concept may explain why agonist.receptor complexes can be inactive and that adopting multiple binding modes may be generalized also to small agonists where binding modes will be only subtly different and confined to only one binding site.