Scientists map activation of prostaglandin E₂ receptor EP1 at atomic level

To overcome the instability of EP1, the researchers employed a multi-pronged engineering strategy, including BRIL fusion, truncation of flexible loops, incorporation of a mini-Gq chimera, and NanoBiT-assisted complex stabilization. They resolved the structure of the EP1–PGE₂–Gq complex at 2.55 Å resolution using single-particle cryo-EM, enabling detailed analysis of both ligand binding and G protein coupling interfaces.

The researchers observed that the activation of EP1 induced a modest outward shift of transmembrane helix 6 (TM6) by approximately 12°, which was notably smaller than the nearly 18° displacement seen in EP2–EP4, suggesting a subtype-specific activation mechanism. In addition, they identified a unique constellation of residues (S42^1.42, H88^2.54, G92^2.58, and F334^7.36) that formed a distinct binding motif for PGE₂, absent in other EP receptors.

Functional assays confirmed that these residues are critical for ligand-induced activation. Notably, the researchers found that EP1 diverged from canonical class A GPCR motifs: It lacks the conserved DRY sequence and features an unusual cysteine at position 3.51, further highlighting its unique signaling profile.

On the intracellular side, the EP1 receptor engaged Gq protein through both conserved and receptor-specific interactions. Residues such as R63^ICL1, E294^6.32, and Q298^6.36 contributed to the precise orientation of the Gα5 helix within the cytoplasmic cavity. Additional compensatory interactions such as those involving S69^2.35 appeared to stabilize G protein coupling, compensating for missing contacts found in related receptors FP and TP.

The findings of this study not only complete the structural framework of PGE₂ signaling through its receptor family, but also provide a blueprint for developing selective EP1-targeted therapies. Given EP1’s involvement in pain, cardiovascular disease, and certain cancers, structure-based drug design informed by this study holds significant translational potential.