Fig. 5: Gα₁₃ activation by GPR55 and selectivity over Gα₁₂.

a Overview of the GPR55-G₁₃-ML184 signaling complex. ML184 and CLR are shown as salmon and green spheres, respectively. Colored rectangles highlight specific G protein interaction sections as described in panels (e, f), respectively. The map quality of one water molecule deviates significantly from four well-resolved water molecules. The modeling of this water molecule was guided by its coordination with R119^3.50, helix VI, and helix VII. b, c G protein dissociation assays of (b) GPR55 and (c) TBXA2R with Gα₁₂ and Gα₁₃. Assays were performed in HEK293H cells transiently transfected with wt Gβ₃, Gγ₉-GFP, and Gα₁₂-Rluc8 or Gα₁₃-Rluc8. Data represents means ± SEM from 3–7 independent experiments as specified in Supplementary Table S3. The negative control data for U-46619 at GPR55 and ML184 or LPI at the TBXA2R was analyzed from three independent experiments. d Sequence alignment of different G protein segments of Gα₁₃ involved in GPR55 binding with the respective residues of Gα₁₂. Black arrows highlight amino acid differences between Gα₁₂ and Gα₁₃ within 4 Å of GPR55. Residues R360 and Q338 are predominantly solvent-exposed and not shown in the following panels. e Protein-protein interface between Gα₁₃ (green cartoon and sticks) and GPR55 (cyan cartoon and sticks) with a focus on the C-terminal α5-helix of Gα₁₃. The cryo-EM composite map (EMDB-51284) for five water molecules is shown with orange mesh. f Protein-protein interactions of residues between the α4-helix and β6-sheet of Gα₁₃ as well as of the initial α5-helix residues with GPR55.