Ligand binding pocket formed by evolutionarily conserved residues in the glucagon-like peptide-1 (GLP-1) receptor core domain.

Glucagon-like peptide-1 (GLP-1) plays a pivotal role in glucose homeostasis through its receptor GLP1R. Due to its multiple beneficial effects, GLP-1 has gained great attention for treatment of type 2 diabetes and obesity. However, little is known about the molecular mechanism underlying the interaction of GLP-1 with the heptahelical core domain of GLP1R conferring high affinity ligand binding and ligand-induced receptor activation. Here, using chimeric and point-mutated GLP1R, we determined that the evolutionarily conserved amino acid residue Arg(380) flanked by hydrophobic Leu(379) and Phe(381) in extracellular loop 3 (ECL3) may have an interaction with Asp(9) and Gly(4) of the GLP-1 peptide. The molecular modeling study showed that Ile(196) at transmembrane helix 2, Met(233) at ECL1, and Asn(302) at ECL2 of GLP1R have contacts with His(1) and Thr(7) of GLP-1. This study may shed light on the mechanism underlying high affinity interaction between the ligand and the binding pocket that is formed by these conserved residues in the GLP1R core domain.