Ligand binding and activation mechanism og the glucagon-like peptide-1 receptor

In recent years, G-protein coupled receptors (GPCRs) have become important drug targets, which makes elucidation of their molecular structure and functional domains increasingly important for designing new and better therapeutic agents. The Glucagon-Like Peptide-1 receptor (GLP-1R) is a GPCR. Its endogenous agonist, Glucagon-Like Peptide-1 (GLP-1), has a number of physiological effects that contribute to reducing blood sugar and body weight.

Therefore, GLP-1R has become a promising target for the treatment of type 2 diabetes (T2D). The overall purpose of the Ph.D. project has been to investigate how GLP-1R interacts with receptor agonists. The thesis includes four studies, which investigate different aspects of these interactions. The first study elucidates GLP-1 binding to the extracellular domain of GLP-1R (ECD) (Study I), whereas the second study identifies receptor domains important for small molecule-mediated activation of GLP-1R (Study II).

A fully functional, cysteine-deprived and Cterminally truncated GLP-1R is developed and characterised in Study III. In Study IV, a cAMP biosensor is used to investigate the cAMP kinetics of GLP-1R upon stimulation with different receptor agonists. Collectively, the work has contributed to a more detailed understanding of GLP-1R pharmacology in a number of ways.

A crystal structure elucidated the molecular details of GLP- 1 binding to the ECD of GLP-1R and supported the existence of different binding modes of GLP-1 and exendin-4. In addition, the work established that seven cysteine residues in GLP-1R and more than half of the C-terminal tail are not required for GLP-1 binding or function.

Last but not least, site-directed mutagenesis identified receptor domains and specific residues involved in small molecule-mediated activation of GLP-1R.