Structural Superimposition

Abstact

Lysophosphatidic acid receptor 5 (LPAR5) is a non-endothelial differentiation gene class A G protein-coupled receptor that regulates neuropathic pain, itch, and cancer progression through coupling to G proteins. Here, we report the cryo-EM structure of LPAR5 bound to 1-oleoyl-lysophosphatidic acid (LPA) in complex with G(q) at 2.96 A resolution, revealing a distinct mode of receptor activation and G protein coupling. The phosphate headgroup of LPA forms extensive polar interactions with residues from extracellular loop 2 and transmembrane helices TM5-TM7, while the lipid tail inserts into a deep hydrophobic cavity formed by TM3-TM5. Site-directed mutagenesis confirms the functional importance of these interactions. Remarkably, LPAR5 exhibits a noncanonical G protein coupling mode. Unlike previously reported GPCR-G protein structures in which the Galpha C-terminal alpha5 helix ("wavy hook") primarily engages TM6, the wavy hook in LPAR5 is positioned toward the intracellular loop 1-helix 8 interface. This configuration is associated with limited TM6 outward displacement and modest rearrangement at the toggle-switch position (6.48). The resulting interface is stabilized by receptor-specific interactions and supported by functional data. Together, these findings reveal an alternative mode of GPCR-G protein coupling and highlight the structural plasticity underlying signaling specificity in LPA receptors.