Characterization of glucagon-like peptide-1 receptor-binding determinants

Abstract

Glucagon-like peptide 1 (GLP-1) is a potent insulinotropic hormone currently under study as a therapeutic agent for type 2 diabetes. Since an understanding of the molecular mechanisms leading to high-affinity receptor (

Mechanisms of action of glucagon-like peptide 1 in the pancreas

“…Together these studies have formulated a picture of how GLP-1 and Ex-4 bind to this receptor and what regions of GLP-1R are important for agonist recognition. The isolated N-terminus of the rat (Lopez de Maturana et al, 2003;Wilmen et al, 1996;Xiao et al, 2000) and human (Bazarsuren et al, 2002) GLP-1R associate with GLP-1, although with lower affinity than with the native receptor (Bazarsuren et al, 2002;Xiao et al, 2000). Similar to the glucagon receptor and other members of this subfamily, GLP-1R has six cysteine residues in the extracellular region that are highly conserved (Thorens et al, 1993).…”

“…1 (W 87 is not essential) and in particular, the imidazole ring of W 39 -are all essential for binding (Wilmen et al, 1996;Wilmen et al, 1997). While Ex-4 interacts primarily with the N-terminal portion of the receptor there is evidence of binding determinants for GLP-1 elsewhere in GLP-1R (Lopez de Maturana et al, 2003): notably residues in the EC 1 and TM 2 domains are of importance (Xiao et al, 2000). Substitution of the negatively charged aspartate residue at 198 in the TM 2 region with the neutral asparagine, does not alter affinity for the receptor indicating that the negative charge is not essential for affinity (Lopez de Maturana and Donnelly, 2002).…”

“…Substitution of the negatively charged aspartate residue at 198 in the TM 2 region with the neutral asparagine, does not alter affinity for the receptor indicating that the negative charge is not essential for affinity (Lopez de Maturana and Donnelly, 2002). In contrast, substitution with alanine, at 198 results in a significant reduction in binding to GLP-1 (Lopez de Maturana and Donnelly, 2002;Xiao et al, 2000). However N-terminally truncated exendin-4 (i.e.…”

“…GLP-1 15-36) maintained their affinity for the receptor with the alanine mutation at 198, demonstrating that the aspartate residue is probably important for association of GLP-1R to the N-terminus of GLP-1. Xiao and colleagues show that further charged residues concentrated at the distal TM 2 /EC 1 region (K 197 , K 202 , D 215 and R 227 ) are also probable binding determinants for GLP-1 (Xiao et al, 2000). Lopez de Maturana performed a further series of double alanine scan mutagenesis studies for the entirety of EC 1 (Lopez de Maturana et al, 2004).…”

International Union of Pharmacology. XXXV. The Glucagon Receptor Family

“…The receptor sequence contains a large hydrophilic, extracellular domain preceded by a short leader sequence required for receptor translocation across the endoplasmic reticulum during biosynthesis, and seven hydrophobic membranespanning domains that are linked by hydrophilic intraand extracellular loops (Thorens and Widmann, 1996). Distinct amino acids within the amino-terminal domain of the receptor are crucial for ligand binding (Parker et al, 1998;Tibaduiza et al, 2001;Wilmen et al, 1997), and the region encompassing transmembrane domains 1 to 3 is also involved in ligand binding (Xiao et al, 2000b). Different domains in the third intracellular loop of the GLP-1 receptor are responsible for specific G proteincoupling (and G␣ s , G i , and G o activation) (Hallbrink et al, 2001), and in the best studied cellular model, islet ␤-cells, GLP-1 receptor signaling acts predominantly via G s to increase cAMP accumulation; however, activation of downstream signaling pathways may occur in a protein kinase A-independent manner (Bode et al, 1999;Holz et al, 1999).…”