Crystal Structure of the Ligand-bound Glucagon-like Peptide-1 Receptor Extracellular Domain

• Published in: The Journal of biological chemistry 2008-04, Vol.283 (17), p.11340-11347
• Main Authors: Runge, Steffen, Thøgersen, Henning, Madsen, Kjeld, Lau, Jesper, Rudolph, Rainer
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Cell Membrane - metabolism; Crystallography, X-Ray - methods; Exenatide; Glucagon-Like Peptide-1 Receptor; Humans; Insulin-Secreting Cells - metabolism; Ligands; Magnetic Resonance Spectroscopy; Molecular Sequence Data; Peptides - chemistry; Protein Binding; Protein Conformation; Protein Structure, Secondary; Receptors, Glucagon - chemistry; Receptors, Glucagon - physiology; Sequence Homology, Amino Acid; Tryptophan - chemistry; Venoms - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M708740200

The glucagon-like peptide-1 receptor (GLP-1R) belongs to Family B1 of the seven-transmembrane G protein-coupled receptors, and its natural agonist ligand is the peptide hormone glucagon-like peptide-1 (GLP-1). GLP-1 is involved in glucose homeostasis, and activation of GLP-1R in the plasma membrane of pancreatic β-cells potentiates glucose-dependent insulin secretion. The N-terminal extracellular domain (nGLP-1R) is an important ligand binding domain that binds GLP-1 and the homologous peptide Exendin-4 with differential affinity. Exendin-4 has a C-terminal extension of nine amino acid residues known as the “Trp cage”, which is absent in GLP-1. The Trp cage was believed to interact with nGLP-1R and thereby explain the superior affinity of Exendin-4. However, the molecular details that govern ligand binding and specificity of nGLP-1R remain undefined. Here we report the crystal structure of human nGLP-1R in complex with the antagonist Exendin-4(9–39) solved by the multiwavelength anomalous dispersion method to 2.2Å resolution. The structure reveals that Exendin-4(9–39) is an amphipathic α-helix forming both hydrophobic and hydrophilic interactions with nGLP-1R. The Trp cage of Exendin-4 is not involved in binding to nGLP-1R. The hydrophobic binding site of nGLP-1R is defined by discontinuous segments including primarily a well defined α-helix in the N terminus of nGLP-1R and a loop between two antiparallel β-strands. The structure provides for the first time detailed molecular insight into ligand binding of the human GLP-1 receptor, an established target for treatment of type 2 diabetes.