Serotonin receptors are important targets for established therapeutics and drug development as they are expressed throughout the human body and play key roles in cell signaling. There are 12 serotonergic G protein-coupled receptor members encoded in the human genome, of which the 5-hydroxytryptamine (5-HT)_5A receptor (5-HT_5AR) is the least understood and lacks selective tool compounds. Here, we report four high-resolution (2.73–2.80 Å) structures of human 5-HT_5ARs, including an inactive state structure bound to an antagonist AS2674723 by crystallization and active state structures bound to a partial agonist lisuride and two full agonists, 5-carboxamidotryptamine (5-CT) and methylergometrine, by cryo-EM. Leveraging the new structures, we developed a highly selective and potent antagonist for 5-HT_5AR. Collectively, these findings both enhance our understanding of this enigmatic receptor and provide a roadmap for structure-based drug discovery for 5-HT_5AR.

血清素受体是已建立的治疗和药物开发的重要靶标，因为它们在整个人体中表达并在细胞信号传导中发挥关键作用。人类基因组中编码有 12 个血清素能 G 蛋白偶联受体成员，其中 5-羟色胺 (5-HT) _5A受体 (5-HT _5A R) 是了解最少且缺乏选择性工具化合物的。_{在这里，我们报告了人类 5-HT 5A} Rs 的四种高分辨率（2.73–2.80 Å）结构，包括通过结晶与拮抗剂 AS2674723 结合的非活性态结构，以及与部分激动剂麦角乙脲和两种完全激动剂结合的活性态结构， 5-甲酰胺色胺 (5-CT) 和甲基麦角新碱，通过冷冻电镜观察。利用新结构，我们开发了一种高度选择性和有效的 5-HT _5A R 拮抗剂。总的来说，这些发现既增强了我们对这种神秘受体的理解，又为基于结构的 5-HT _5A R药物发现提供了路线图。