羟基羧酸受体3（HCAR3）是一种A类G蛋白偶联受体，是一种重要的细胞能量代谢传感器，在人体脂肪分解调节中发挥关键作用。 HCAR3深度参与多种生理过程，是代谢性疾病、肿瘤、免疫疾病治疗的重要靶点。在这里，我们报道了含有或不含激动剂的人类 HCAR3-Gi1 复合物的四种冷冻电镜 (cryo-EM) 结构：内源性配体 3-羟基辛酸、药物烟酸、高度亚型特异性的激动剂化合物 5c (4-(n-丙基)氨基-3-硝基苯甲酸)，以及apo形式。结合诱变和功能分析，我们揭示了 HCAR3 对不同激动剂的识别机制。此外，还阐明了决定HCAR2和HCAR3之间配体选择性的关键残基。总体而言，这些发现为HCAR3的配体识别、激活和选择性以及G蛋白偶联机制提供了结构基础，有助于设计具有高效能和选择性的HCAR3靶向药物。版权所有©2024 。由爱思唯尔公司出版。保留所有权利。

Hydroxycarboxylic acid receptor 3 (HCAR3), a class A G-protein-coupled receptor, is an important cellular energy metabolism sensor with a key role in the regulation of lipolysis in humans. HCAR3 is deeply involved in many physiological processes and serves as a valuable target for the treatment of metabolic diseases, tumors, and immune diseases. Here, we report four cryoelectron microscopy (cryo-EM) structures of human HCAR3-Gi1 complexes with or without agonists: the endogenous ligand 3-hydroxyoctanoic acid, the drug niacin, the highly subtype-specific agonist compound 5c (4-(n-propyl)amino-3-nitrobenzoic acid), and the apo form. Together with mutagenesis and functional analyses, we revealed the recognition mechanisms of HCAR3 for different agonists. In addition, the key residues that determine the ligand selectivity between HCAR2 and HCAR3 were also illuminated. Overall, these findings provide a structural basis for the ligand recognition, activation, and selectivity and G-protein coupling mechanisms of HCAR3, which contribute to the design of HCAR3-targeting drugs with high efficacy and selectivity.Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.