Institute for Pharmaceutical and Medicinal Chemistry, Heinrich Heine University, Universitätsstr. 1, 40225 Düsseldorf, Germany.
Clinic for Gastroenterology, Hepatology, and Infectious Diseases, Heinrich Heine University, Universitätsstr. 1, 40225 Düsseldorf, Germany.
Eur J Med Chem. 2015 Nov 2;104:57-72. doi: 10.1016/j.ejmech.2015.09.024. Epub 2015 Sep 24.
TGR5 (Gpbar-1, M-Bar) is a class A G-protein coupled bile acid-sensing receptor predominately expressed in brain, liver and gastrointestinal tract, and a promising drug target for the treatment of metabolic disorders. Due to the lack of a crystal structure of TGR5, the development of TGR5 agonists has been guided by ligand-based approaches so far. Three binding mode models of bile acid derivatives have been presented recently. However, they differ from one another in terms of overall orientation or with respect to the location and interactions of the cholane scaffold, or cannot explain all results from mutagenesis experiments. Here, we present an extended binding mode model based on an iterative and integrated computational and biological approach. An alignment of 68 TGR5 agonists based on this binding mode leads to a significant and good structure-based 3D QSAR model, which constitutes the most comprehensive structure-based 3D-QSAR study of TGR5 agonists undertaken so far and suggests that the binding mode model is a close representation of the "true" binding mode. The binding mode model is further substantiated in that effects predicted for eight mutations in the binding site agree with experimental analyses on the impact of these TGR5 variants on receptor activity. In the binding mode, the hydrophobic cholane scaffold of taurolithocholate orients towards the interior of the orthosteric binding site such that rings A and B are in contact with TM5 and TM6, the taurine side chain orients towards the extracellular opening of the binding site and forms a salt bridge with R79(EL1), and the 3-hydroxyl group forms hydrogen bonds with E169(5.44) and Y240(6.51). The binding mode thus differs in important aspects from the ones recently presented. These results are highly relevant for the development of novel, more potent agonists of TGR5 and should be a valuable starting point for the development of TGR5 antagonists, which could show antiproliferative effects in tumor cells.
TGR5（Gpbar-1，M 受体）是一种 A 类 G 蛋白偶联胆汁酸感应受体，主要表达于脑、肝和胃肠道，是治疗代谢紊乱的有前途的药物靶点。由于缺乏 TGR5 的晶体结构，迄今为止，TGR5 激动剂的开发一直以配体为基础的方法为指导。最近提出了三种胆汁酸衍生物的结合模式模型。然而，它们在整体取向或胆烷支架的位置和相互作用方面存在差异，或者不能解释所有的突变体实验结果。在这里，我们提出了一个基于迭代和综合计算和生物学方法的扩展结合模式模型。基于该结合模式对 68 种 TGR5 激动剂进行对齐，得到了一个显著的和良好的基于结构的 3D-QSAR 模型，这是迄今为止对 TGR5 激动剂进行的最全面的基于结构的 3D-QSAR 研究，并表明结合模式模型是对“真实”结合模式的一个很好的代表。该结合模式模型进一步得到证实，因为对结合位点 8 个突变的预测作用与这些 TGR5 变体对受体活性的影响的实验分析一致。在结合模式中，牛磺胆酸的疏水性胆烷支架朝向正位结合位点的内部定向，使得环 A 和环 B 与 TM5 和 TM6 接触，牛磺酸侧链朝向结合位点的细胞外开口定向，并与 R79（EL1）形成盐桥，3-羟基与 E169（5.44）和 Y240（6.51）形成氢键。因此，该结合模式在重要方面与最近提出的模式不同。这些结果对于开发新型、更有效的 TGR5 激动剂具有重要意义，并且应该是开发 TGR5 拮抗剂的有价值的起点，TGR5 拮抗剂可能在肿瘤细胞中显示出抗增殖作用。
