FIGURE 1.

Differential effects of human GLP-1R and human GCGR point mutations on GLP-1 and glucagon binding. A, comparison of the effects of 66 GLP-1R point mutations on GLP-1 binding and 66 GCGR mutations on glucagon binding, based on IC₅₀ values in ¹²⁵I-GLP-1 (for GLP-1R) and ¹²⁵I-glucagon (for GCGR) displacement assays (including 50 GCGR mutants determined previously (11)). Mutated residues that had <4-fold change (blue), 4–10-fold increase (orange), and >10-fold increase (red) in IC₅₀ values for GLP-1 binding to GLP-1R or glucagon binding to GCGR are shown. Mutant receptors with expression <30% of wild-type are colored gray. For each position, the results of mutations that show the most distinct differences between GLP-1R and GCGR are reported (see Table 1). The effects of previously reported human GLP-1R mutants are presented in supplemental Table S1 (7, 8, 19, 20, 25, 28–30, 32) and rat GLP-1R mutation data in supplemental Table S2 (26, 27). The most conserved residues in TM helices 1–7 of class B GPCRs (19) are boxed. B–D, representative ¹²⁵I-GLP-1/GLP-1R (B and D) and ¹²⁵I-glucagon/GCGR (C) displacement dose-response curves. Data are expressed as a percentage of specific ¹²⁵I-GLP-1 or ¹²⁵I-glucagon binding in the presence of 3.57 pm unlabeled peptide. Each point (±S.E.) represents the mean value of at least three independent experiments done in triplicate (IC₅₀ data presented in Table 1 and supplemental Tables S1 and S3).