The bioactive lysophospholipid sphingosine-1-phosphate (S1P) acts via five different subtypes of S1P receptors (S1PRs) - S1P_1-5. S1P₅ is predominantly expressed in nervous and immune systems, regulating the egress of natural killer cells from lymph nodes and playing a role in immune and neurodegenerative disorders, as well as carcinogenesis. Several S1PR therapeutic drugs have been developed to treat these diseases; however, they lack receptor subtype selectivity, which leads to side effects. In this article, we describe a 2.2 Å resolution room temperature crystal structure of the human S1P₅ receptor in complex with a selective inverse agonist determined by serial femtosecond crystallography (SFX) at the Pohang Accelerator Laboratory X-Ray Free Electron Laser (PAL-XFEL) and analyze its structure-activity relationship data. The structure demonstrates a unique ligand-binding mode, involving an allosteric sub-pocket, which clarifies the receptor subtype selectivity and provides a template for structure-based drug design. Together with previously published S1PR structures in complex with antagonists and agonists, our structure with S1P₅-inverse agonist sheds light on the activation mechanism and reveals structural determinants of the inverse agonism in the S1PR family.

生物活性溶血磷脂 1-磷酸鞘氨醇 (S1P) 通过五种不同亚型的 S1P 受体 (S1PR) - S1P _1-5发挥作用。 S1P ₅主要在神经和免疫系统中表达，调节自然杀伤细胞从淋巴结的排出，并在免疫和神经退行性疾病以及癌发生中发挥作用。已经开发出几种S1PR治疗药物来治疗这些疾病；然而，它们缺乏受体亚型选择性，这会导致副作用。在本文中，我们描述了人类 S1P ₅受体与选择性反向激动剂复合物的 2.2 Å 分辨率室温晶体结构，该结构通过浦项加速器实验室 X 射线自由电子激光器 (PAL-XFEL) 的系列飞秒晶体学 (SFX) 测定）并分析其结构-活性关系数据。该结构展示了一种独特的配体结合模式，涉及变构子口袋，阐明了受体亚型选择性，并为基于结构的药物设计提供了模板。与之前发表的与拮抗剂和激动剂复合的S1PR结构一起，我们的S1P _5-反向激动剂结构揭示了激活机制，并揭示了S1PR家族中反向激动的结构决定因素。