Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, USA.
Molecules. 2021 Sep 5;26(17):5397. doi: 10.3390/molecules26175397.
After we identified pGlu-βGlu-Pro-NH as the first functional antagonist of the cholinergic central actions of the thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH), we became interested in finding the receptor-associated mechanism responsible for this antagonism. By utilizing a human TRH receptor (hTRH-R) homology model, we first refined the active binding site within the transmembrane bundle of this receptor to enhance TRH's binding affinity. However, this binding site did not accommodate the TRH antagonist. This directed us to consider a potential allosteric binding site in the extracellular domain (ECD). Searches for ECD binding pockets prompted the remodeling of the extracellular loops and the -terminus. We found that different trajectories of ECDs produced novel binding cavities that were then systematically probed with TRH, as well as its antagonist. This led us to establish not only a surface-recognition binding site for TRH, but also an allosteric site that exhibited a selective and high-affinity binding for pGlu-βGlu-Pro-NH. The allosteric binding of this TRH antagonist is more robust than TRH's binding to its own active site. The findings reported here may shed light on the mechanisms and the multimodal roles by which the ECD of a TRH receptor is involved in agonist and/or antagonist actions.
在鉴定出 pGlu-βGlu-Pro-NH 是促甲状腺素释放激素 (TRH，pGlu-His-Pro-NH) 对中枢胆碱能作用的第一个功能性拮抗剂之后，我们对发现负责这种拮抗作用的受体相关机制产生了兴趣。通过利用人促甲状腺素释放激素受体 (hTRH-R) 同源模型，我们首先对该受体跨膜束内的活性结合位点进行了精细化处理，以增强 TRH 的结合亲和力。然而，这个结合位点容纳不下 TRH 的拮抗剂。这促使我们考虑在细胞外域 (ECD) 中存在潜在的变构结合位点。对 ECD 结合口袋的搜索促使细胞外环和 -末端发生重塑。我们发现，ECD 的不同轨迹产生了新的结合腔，然后用 TRH 以及其拮抗剂对这些结合腔进行了系统探测。这使我们不仅建立了 TRH 的表面识别结合位点，还建立了一个变构结合位点，该结合位点对 pGlu-βGlu-Pro-NH 表现出选择性和高亲和力的结合。这种 TRH 拮抗剂的变构结合比 TRH 与其自身活性位点的结合更牢固。这里报道的发现可能阐明了 ECD 参与激动剂和/或拮抗剂作用的机制和多模态作用。
