The major determinant of exendin‐4/glucagon‐like peptide 1 differential affinity at the rat glucagon‐like peptide 1 receptor N‐terminal domain is a hydrogen bond from SER‐32 of exendin‐4

• Published in: British journal of pharmacology Vol. 160; no. 8; pp. 1973 - 1984
• Main Authors: Mann, RJ, Nasr, NE, Sinfield, JK, Paci, E, Donnelly, D
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-08-2010; Nature Publishing Group
• Subjects: Animals; Aspartic Acid; Binding Sites; Binding, Competitive; Biological and medical sciences; Cell Line; diabetes; Diabetes. Impaired glucose tolerance; Endocrine pancreas. Apud cells (diseases); Endocrinopathies; Etiopathogenesis. Screening. Investigations. Target tissue resistance; Exenatide; exendin‐4; GLP‐1; Glucagon-Like Peptide-1 Receptor; Glutamic Acid; GPCR; hormone; Humans; Hydrogen Bonding; Hydrogen bonds; Hypoglycemic Agents - chemistry; Hypoglycemic Agents - metabolism; Hypoglycemic Agents - pharmacology; ligand; Medical sciences; Models, Molecular; Molecular Structure; Mutagenesis, Site-Directed; Peptides; Peptides - chemistry; Peptides - metabolism; Peptides - pharmacology; Pharmacology. Drug treatments; Protein Conformation; Protein Structure, Tertiary; Radioligand Assay; Rats; receptor; Receptors, Glucagon - chemistry; Receptors, Glucagon - genetics; Receptors, Glucagon - metabolism; Recombinant Proteins - chemistry; Research Papers; Serine; Structure-Activity Relationship; Transfection; Venoms - chemistry; Venoms - metabolism; Venoms - pharmacology; Endocrinopathy; GLP-1; Rat; Ligand; Diabetes mellitus; Rodentia; Exenatide; Glucagon like peptide 1; hormone; Vertebrata; Hypoglycemic agent; Gastrointestinal hormone; Mammalia; receptor; G protein coupled receptor; Analog; Animal; Affinity; GPCR; diabetes; exendin-4; Hydrogen bond; Biological receptor
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.2010.00834.x

BACKGROUND AND PURPOSE
Exendin‐4 (exenatide, Ex4) is a high‐affinity peptide agonist at the glucagon‐like peptide‐1 receptor (GLP‐1R), which has been approved as a treatment for type 2 diabetes. Part of the drug/hormone binding site was described in the crystal structures of both GLP‐1 and Ex4 bound to the isolated N‐terminal domain (NTD) of GLP‐1R. However, these structures do not account for the large difference in affinity between GLP‐1 and Ex4 at this isolated domain, or for the published role of the C‐terminal extension of Ex4. Our aim was to clarify the pharmacology of GLP‐1R in the context of these new structural data.
EXPERIMENTAL APPROACH
The affinities of GLP‐1, Ex4 and various analogues were measured at human and rat GLP‐1R (hGLP‐1R and rGLP‐1R, respectively) and various receptor variants. Molecular dynamics coupled with in silico mutagenesis were used to model and interpret the data.
KEY RESULTS
The membrane‐tethered NTD of hGLP‐1R displayed similar affinity for GLP‐1 and Ex4 in sharp contrast to previous studies using the soluble isolated domain. The selectivity at rGLP‐1R for Ex4(9–39) over Ex4(9–30) was due to Ser‐32 in the ligand. While this selectivity was not observed at hGLP‐1R, it was regained when Glu‐68 of hGLP‐1R was mutated to Asp.
CONCLUSIONS AND IMPLICATIONS
GLP‐1 and Ex4 bind to the NTD of hGLP‐1R with similar affinity. A hydrogen bond between Ser32 of Ex4 and Asp‐68 of rGLP‐1R, which is not formed with Glu‐68 of hGLP‐1R, is responsible for the improved affinity of Ex4 at the rat receptor.