Fig. 3. Specific engagement of TAP with EP2.

(A) Detail interactions of TAP (marine) with EP2 (orange) were shown. H-bonds were depicted as red dashed lines. (B) 2D representation of contacts between EP2 with the ligand TAP. The polar bonds were presented by red dotted lines. Residues F188^ECL2 and W186^ECL2 that were implicated in hydrophobic interactions with the region A subpocket were presented in green. T82^2.54 and S86^2.58 formed stronger H-bond engagements with the region B subpocket and were presented in blue. The hydrophobic contacts of EP2 with TAP were colored pink. (C and D) Effects of mutations of TAP contacting residues in ligand binding and G_s signaling. The competitive binding curve of TAP toward EP2 was created using ³H-PGE₂ as the isotope probe (C). Bars represent the differences in calculated potency of TAP (△pEC₅₀) for each mutation according to wild-type (WT) EP2. ***P < 0.0001 [one-way analysis of variance (ANOVA) compared with the response of WT] (D). See fig. S5 (E and F) for detailed statistical evaluation and fig. S4D for receptor expression levels. (E) Sequence alignment of prostonoid receptors. Note that the combination of F112^3.28 and L301^7.39 was only found in EP2, DP1, and FP; I85^2.57, F119^3.35, S305^7.43, and S308^7.46exhibited great diversity among prostonoid receptor families.