title: A small molecule ligand of the glucagon-like peptide 1 receptor targets its amino-terminal hormone binding domain.
abstract: The glucagon-like peptide 1 receptor (GLP-1R) belongs to a distinct subgroup of G protein-coupled peptide hormone receptors (class B) that has been difficult to target by small molecule drugs. Here, we report that a non-peptide compound, T-0632, binds with micromolar affinity to the human GLP-1R and blocks GLP-1-induced cAMP production. Furthermore, the observation that T-0632 has almost 100-fold selectivity for the human versus the highly homologous rat GLP-1R provided an opportunity to map determinants of non-peptide binding. Radioligand competition experiments utilizing a series of chimeric human/rat GLP-1R constructs revealed that partial substitution of the amino terminus of the rat GLP-1R with the corresponding sequence from the human homolog was sufficient to confer high T-0632 affinity. Follow-up analysis of receptors where individual candidate amino acids had been exchanged between the human and rat GLP-1Rs identified a single residue that explained species selectivity of non-peptide binding. Replacement of tryptophan 33 in the human GLP-1R by serine (the homologous amino acid in the rat GLP-1R) resulted in a 100-fold loss of T-0632 affinity, whereas the converse mutation in the rat GLP-1R led to a reciprocal gain-of-function phenotype. These observations suggest that in a class B receptor, important determinants of non-peptide affinity reside within the extracellular amino-terminal domain. Compound T-0632 may mimic, and thereby interfere with, the putative "pseudo-tethering" mechanism by which the amino terminus of class B receptors initiates the binding of cognate hormones.
authors.affiliation: Department of Medicine and Molecular Pharmacology Research Center, Tupper Research Institute, New England Medical Center, Boston, Massachusetts 02111, USA.
authors.forename: E C
authors.initials: EC
authors.lastname: Tibaduiza
authors.forename: C
authors.initials: C
authors.lastname: Chen
authors.forename: M
authors.initials: M
authors.lastname: Beinborn
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D019556:COS Cells; D000067757:Glucagon-Like Peptide-1 Receptor; D006801:Humans; D007211:Indoles / Q000378:metabolism; D008024:Ligands; D009154:Mutation; D018027:Receptors, Glucagon / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C000593833:GLP1R protein, human; C000593835:Glp1r protein, rat; D000067757:Glucagon-Like Peptide-1 Receptor; D007211:Indoles; D008024:Ligands; D018027:Receptors, Glucagon; C103722:T 0632