Figure 5.

PGD₂ binding. (A) Potential binding pocket for PGD₂ as shown by the transparent grey cavity. The polar residues that may be involved in the interactions with the carboxylate group in PGD₂ are labeled in purple. (B) Cell surface expression levels of wild-type CRTH2 (wtCRTH2) and three mutants (left) and their specific saturation binding of ³H-PGD₂ (right). The cell surface expression of each construct in HEK-293T cells was assessed by measuring the binding of fluorescent anti-FLAG antibodies to the FLAG epitope displayed at the N-terminus of the receptor through flow cytometry. The specific saturation binding assays were performed using cell membranes. The W283A mutant is shown as a positive control, in which the binding of PGD₂ was not significantly altered. Data points are presented as the mean values +/− SEM, n=3. (C) Succinate (pink) and propylene glycol (brown) molecules modeled in the structures of fevipiprant-bound CRTH2 (blue) and CAY10471-bound CRTH2 (slate). The hydrogen bonds are shown as black dashed lines. (D) Charge distribution of the ligand-binding pocket of CRTH2 (open-book view). Fevipiprant is shown as orange sticks. (E) Cartoon diagram of the proposed PGD₂ binding process. The positive charge potential is indicated as “+”. The lipid bilayer is shown as the pink background. The carboxylate group in PGD₂ is colored in green, while the rest hydrophobic moiety of PGD₂ is colored in yellow.