Prostaglandin D₂ (PGD₂) signals through the G protein–coupled receptor (GPCR) CRTH2 to mediate various inflammatory responses. CRTH2 is the only member of the prostanoid receptor family that is phylogenetically distant from others, implying a nonconserved mechanism of lipid action on CRTH2. Here, we report a crystal structure of human CRTH2 bound to a PGD₂ derivative, 15R-methyl-PGD₂ (15mPGD₂), by serial femtosecond crystallography. The structure revealed a “polar group in”–binding mode of 15mPGD₂ contrasting the “polar group out”–binding mode of PGE₂ in its receptor EP3. Structural comparison analysis suggested that these two lipid-binding modes, associated with distinct charge distributions of ligand-binding pockets, may apply to other lipid GPCRs. Molecular dynamics simulations together with mutagenesis studies also identified charged residues at the ligand entry port that function to capture lipid ligands of CRTH2 from the lipid bilayer. Together, our studies suggest critical roles of charge environment in lipid recognition by GPCRs.

前列腺素 D ₂ (PGD ₂ ) 通过 G 蛋白偶联受体 (GPCR) CRTH2 发出信号以介导各种炎症反应。CRTH2 是前列腺素受体家族中唯一在系统发育上远离其他受体的成员，这意味着脂质对 CRTH2 的作用是非保守机制。在这里，我们通过连续飞秒晶体学报告了与 PGD ₂衍生物 15R-甲基-PGD ₂ (15mPGD ₂ )结合的人 CRTH2 的晶体结构。该结构揭示了 15mPGD ₂的“极性基团输入”-结合模式，与 PGE _{2的“极性基团输出”-结合模式形成对比}在其受体 EP3 中。结构比较分析表明，这两种脂质结合模式与配体结合口袋的不同电荷分布相关，可能适用于其他脂质 GPCR。分子动力学模拟以及诱变研究还确定了配体入口处的带电残基，其功能是从脂质双层中捕获 CRTH2 的脂质配体。总之，我们的研究表明电荷环境在 GPCR 识别脂质中的关键作用。