Identification of GLP-1-interacting residues in the second half of GLP1R ECL3.
A, the potency of GLP-1 toward chimeric GLP1R, which has the second half of VPAC1R ECL3 (G/V[E3b]), or mutant G/V[E3b], into which residues from GLP1R ECL3 were introduced. B, schematic diagram for ECL3 mutations and log EC50 values of GLP-1. The diagram shows that amino acid residues Leu379, Arg380, Phe381, and/or Leu384 were reintroduced into G/V[E3b]. The data on the sigmoidal curves and EC50 values represent the means ± S.E. of at least three independent experiments. a, versus wild-type GLP1R (p < 0.05); b, versus G/V[E3b] (p < 0.05).