Maintaining pH at cellular, tissular, and systemic levels is essential for human health. Proton-sensing GPCRs regulate physiological and pathological processes by sensing the extracellular acidity. However, the molecular mechanism of proton sensing and activation of these receptors remains elusive. Here, we present cryoelectron microscopy (cryo-EM) structures of human GPR4, a prototypical proton-sensing GPCR, in its inactive and active states. Our studies reveal that three extracellular histidine residues are crucial for proton sensing of human GPR4. The binding of protons induces substantial conformational changes in GPR4's ECLs, particularly in ECL2, which transforms from a helix-loop to a β-turn-β configuration. This transformation leads to the rearrangements of H-bond network and hydrophobic packing, relayed by non-canonical motifs to accommodate G proteins. Furthermore, the antagonist NE52-QQ57 hinders human GPR4 activation by preventing hydrophobic stacking rearrangement. Our findings provide a molecular framework for understanding the activation mechanism of a human proton-sensing GPCR, aiding future drug discovery.
Organizational Affiliation:
Department of Pathology of Sir Run Run Shaw Hospital, Department of Pharmacology, MOE Frontier Science Center for Brain Research and Brain-Machine Integration, and Liangzhu Laboratory, Zhejiang University School of Medicine, Hangzhou 310058, China.
Medical Basic Research Innovation Center for Cardiovascular and Cerebrovascular Diseases, Ministry of Education, School of Pharmacy, Nanjing Medical University, Nanjing 211166, China.
Department of Pathology of Sir Run Run Shaw Hospital, Department of Pharmacology, MOE Frontier Science Center for Brain Research and Brain-Machine Integration, and Liangzhu Laboratory, Zhejiang University School of Medicine, Hangzhou 310058, China; State Key Laboratory of Digital Medical Engineering, Department of Otolaryngology Head and Neck Surgery, Zhongda Hospital, School of Life Sciences and Technology, School of Medicine, Advanced Institute for Life and Health, Jiangsu Province High-Tech Key Laboratory for Bio-Medical Research, Southeast University, Nanjing 210096, China.
Department of Pathology of Sir Run Run Shaw Hospital, Department of Pharmacology, MOE Frontier Science Center for Brain Research and Brain-Machine Integration, and Liangzhu Laboratory, Zhejiang University School of Medicine, Hangzhou 310058, China; Institute of Cytology and Genetics, School of Basic Medical Sciences, Hengyang Medical School, University of South China, Hengyang, Hunan 421001, China.
State Key Laboratory of Digital Medical Engineering, Department of Otolaryngology Head and Neck Surgery, Zhongda Hospital, School of Life Sciences and Technology, School of Medicine, Advanced Institute for Life and Health, Jiangsu Province High-Tech Key Laboratory for Bio-Medical Research, Southeast University, Nanjing 210096, China.
College of Computer Science and Technology, Zhejiang University, Hangzhou 310027, China.
Department of Pharmacology, Zhejiang University School of Medicine, Hangzhou 310058, China.
Medical Basic Research Innovation Center for Cardiovascular and Cerebrovascular Diseases, Ministry of Education, School of Pharmacy, Nanjing Medical University, Nanjing 211166, China. Electronic address: fenghan169@njmu.edu.cn.
Department of Pathology of Sir Run Run Shaw Hospital, Department of Pharmacology, MOE Frontier Science Center for Brain Research and Brain-Machine Integration, and Liangzhu Laboratory, Zhejiang University School of Medicine, Hangzhou 310058, China; Center for Structural Pharmacology and Therapeutics Development, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310016, China; Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310016, China. Electronic address: maochunyou@zju.edu.cn.
Department of General Surgery, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou 310016, China; National Engineering Research Center of Innovation and Application of Minimally Invasive Instruments, Hangzhou 310016, China; Zhejiang Minimal Invasive Diagnosis and Treatment Technology Research Center of Severe Hepatobiliary Disease, Hangzhou 310016, China. Electronic address: srrsh_cxj@zju.edu.cn.
Department of Pathology of Sir Run Run Shaw Hospital, Department of Pharmacology, MOE Frontier Science Center for Brain Research and Brain-Machine Integration, and Liangzhu Laboratory, Zhejiang University School of Medicine, Hangzhou 310058, China. Electronic address: zhang_yan@zju.edu.cn.
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