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. 2025 Feb 6;188(3):653-670.e24.
doi: 10.1016/j.cell.2024.12.001. Epub 2025 Jan 2.

Evolutionary study and structural basis of proton sensing by Mus GPR4 and Xenopus GPR4

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Evolutionary study and structural basis of proton sensing by Mus GPR4 and Xenopus GPR4

Xin Wen et al. Cell. .

Abstract

Animals have evolved pH-sensing membrane receptors, such as G-protein-coupled receptor 4 (GPR4), to monitor pH changes related to their physiology and generate adaptive reactions. However, the evolutionary trajectory and structural mechanism of proton sensing by GPR4 remain unresolved. Here, we observed a positive correlation between the optimal pH of GPR4 activity and the blood pH range across different species. By solving 7-cryoelectron microscopy (cryo-EM) structures of Xenopus tropicalis GPR4 (xtGPR4) and Mus musculus GPR4 (mmGPR4) under varying pH conditions, we identified that protonation of HECL2-45.47 and H7.36 enabled polar network establishment and tighter association between the extracellular loop 2 (ECL2) and 7 transmembrane (7TM) domain, as well as a conserved propagating path, which are common mechanisms underlying protonation-induced GPR4 activation across different species. Moreover, protonation of distinct extracellular HECL2-45.41 contributed to the more acidic optimal pH range of xtGPR4. Overall, our study revealed common and distinct mechanisms of proton sensing by GPR4, from a structural, functional, and evolutionary perspective.

Keywords: GPCR; GPR4; cryo-EM; evolution; proton sensing.

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Conflict of interest statement

Declaration of interests The authors declare no competing interests.

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