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Researchers determined high-resolution cryo-EM structures of the GPR174 receptor bound to two different G proteins (Gs at 2.0 Angstrom and Gi at 3.4 Angstrom), revealing that structured water molecules form a continuous intracellular network linking key functional motifs including the sodium-binding pocket, the NPxxY and DRY motifs, and the G protein-binding interface. This hydration network stabilizes the active conformation of the receptor and reshapes its intracellular cavity in ways that allow selective coupling to either Gs or Gi. Through molecular dynamics simulations and functional assays, the authors further identified three conserved hydration cavities across class A GPCRs, whose composition is partly determined by residue properties at position 5.58.
Why it matters
GPR174 plays a role in regulating autoimmune responses and immune homeostasis, so understanding its activation mechanism at atomic resolution could inform the design of selective therapeutics targeting autoimmune diseases. More broadly, the framework for water-mediated regulation described here may guide drug discovery efforts across the large and pharmacologically important class A GPCR family.
by Ying-Jun Dong, Kun Xi, Ya-Zhi Zhang, Jian-Heng Xue, Dan-Dan Shen, Shao-Kun Zang, Ruozhu Zhao, Hai Qi, Chunyou Mao, Wei-Wei Wang, Yan Zhang
G protein-coupled receptor 174 (GPR174), a key modulator of autoimmune responses, maintains immune homeostasis through distinct G protein signaling pathways, particularly Gs and Gi. Although the structural mechanism of lysophosphatidylserine (LysoPS)-activated GPR174 in the Gs pathway has been characterized, how hydration-mediated interactions influence GPR174 activation and signaling selectivity remains unclear. Here, we determined high-resolution cryo-electron microscopy (cryo-EM) structures of LysoPS-activated human GPR174 bound to Gs (2.0 Å) and Gi (3.4 Å), revealing a continuous hydration-mediated signal transduction network that bridges the sodium-binding pocket, the NPxxY and DRY motifs, and the G protein-binding interface. This network stabilizes the active-state conformation of GPR174 and dynamically reshapes the intracellular cavity, thereby enabling differential engagement of Gs and Gi. Molecular dynamics simulations and functional assays demonstrated that the hydration network is essential for receptor activation and selectively modulates G protein coupling. To evaluate its conservation, we performed sequence alignments and structural analyses across class A GPCRs, defining three hydration cavities: the conserved water cavity (CWC), the junctional water cavity (JWC), and the extended water cavity (EWC), whose hydration is determined by residue properties at position 5.58. Together, our study reveals a hydration-driven molecular mechanism that underlies the activation of GPR174 and its dual G protein selectivity. These findings advance the understanding of hydration-mediated signaling in GPR174 and provide a framework for investigating water-mediated regulation across class A GPCRs.
Source: Structured water molecules drive activation and G protein selectivity in the GPR174 receptor