title: Structural Mapping and Functional Characterization of Zebrafish Class B G-Protein Coupled Receptor (GPCR) with Dual Ligand Selectivity towards GLP-1 and Glucagon.
abstract: GLP-1 and glucagon regulate glucose metabolism through a network of metabolic pathways initiated upon binding to their specific receptors that belong to class B G-protein coupled receptors (GPCRs). The therapeutic potential of glucagon is currently being evaluated, while GLP-1 is already used in the treatment of type 2 diabetes and obesity. Development of a second generation of GLP-1 based therapeutics depends on a molecular and structural understanding of the interactions between the GLP-1 receptor (GLP-1R) and its ligand GLP-1. There is considerable sequence conservation between GLP-1 and glucagon and between the hGLP-1R and human glucagon receptor (hGCGR), yet each receptor recognizes only its own specific ligand. Glucagon receptors in fish and frogs also exhibit ligand selectivity only towards glucagon and not GLP-1. Based on competitive binding experiments and assays of increase in intracellular cAMP, we demonstrate here that a GPCR in zebrafish (Danio rerio) exhibits dual ligand selectivity towards GLP-1 and glucagon, a characteristic not found in mammals. Further, many structural features found in hGLP-1R and hGCGR are also found in this zebrafish GPCR (zfGPCR). We show this by mapping of its sequence and structural features onto the hGLP-1R and hGCGR based on their partial and complementary crystal structures. Thus, we propose that zfGPCR represents a dual GLP-1R/GCGR. The main differences between the three receptors are in their stalk regions that connect their N-terminal extracellular domains (NECDs) with their transmembrane domains and the absence of loop 3 in the NECD in zfGLP-1R/GCGR. These observations suggest that the interactions between GLP-1 and glucagon with loop 3 and the stalk regions may induce different conformational changes in hGLP-1R and hGCGR upon ligand binding and activation that lead to selective recognition of their native ligands.
authors.affiliation: The Rockefeller University, New York, New York, United States of America.
authors.forename: Deena A
authors.initials: DA
authors.lastname: Oren
authors.affiliation: The Rockefeller University, New York, New York, United States of America.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wei
authors.affiliation: Applied Bioinformatics Core, Weill Cornell Medical College, New York, New York, United States of America.
authors.forename: Luce
authors.initials: L
authors.lastname: Skrabanek
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China.
authors.forename: Billy K C
authors.initials: BK
authors.lastname: Chow
authors.affiliation: Department of Biochemistry, University of Victoria, Victoria, British Columbia, Canada.
authors.forename: Thomas
authors.initials: T
authors.lastname: Mommsen
authors.affiliation: The Rockefeller University, New York, New York, United States of America.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Mojsov
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005934:Glucagon / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism*; D008024:Ligands; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015027:Zebrafish / Q000378:metabolism*
chemical_list: D008024:Ligands; D043562:Receptors, G-Protein-Coupled; D052216:Glucagon-Like Peptide 1; D005934:Glucagon