Jesper Lau

Liraglutide is an acylated glucagon-like peptide-1 (GLP-1) analogue that binds to serum albumin in vivo and is approved for once-daily treatment of diabetes as well as obesity. The aim of the present studies was to design a once weekly GLP-1 analogue by increasing albumin affinity and secure full stability against metabolic degradation. The fatty acid moiety and the linking chemistry to GLP-1 were the key features to secure high albumin affinity and GLP-1 receptor (GLP-1R) potency and in obtaining a prolonged exposure and action of the GLP-1 analogue. Semaglutide was selected as the optimal once weekly candidate. Semaglutide has two amino acid substitutions compared to human GLP-1 (Aib(8), Arg(34)) and is derivatized at lysine 26. The GLP-1R affinity of semaglutide (0.38 ± 0.06 nM) was three-fold decreased compared to liraglutide, whereas the albumin affinity was increased. The plasma half-life was 46.1 h in mini-pigs following i.v. administration, and semaglutide has an MRT of 63.6 h after s.c. dosing to mini-pigs. Semaglutide is currently in phase 3 clinical testing.

The discovery of glucagon-like peptide-1 (GLP-1), an incretin hormone with important effects on glycemic control and body weight regulation, led to efforts to extend its half-life and make it therapeutically effective in people with type 2 diabetes (T2D). The development of short- and then long-acting GLP-1 receptor agonists (GLP-1RAs) followed. Our article charts the discovery and development of the long-acting GLP-1 analogs liraglutide and, subsequently, semaglutide. We examine the chemistry employed in designing liraglutide and semaglutide, the human and non-human studies used to investigate their cellular targets and pharmacological effects, and ongoing investigations into new applications and formulations of these drugs. Reversible binding to albumin was used for the systemic protraction of liraglutide and semaglutide, with optimal fatty acid and linker combinations identified to maximize albumin binding while maintaining GLP-1 receptor (GLP-1R) potency. GLP-1RAs mediate their effects via this receptor, which is expressed in the pancreas, gastrointestinal tract, heart, lungs, kidneys, and brain. GLP-1Rs in the pancreas and brain have been shown to account for the respective improvements in glycemic control and body weight that are evident with liraglutide and semaglutide. Both liraglutide and semaglutide also positively affect cardiovascular (CV) outcomes in individuals with T2D, although the precise mechanism is still being explored. Significant weight loss, through an effect to reduce energy intake, led to the approval of liraglutide (3.0 mg) for the treatment of obesity, an indication currently under investigation with semaglutide. Other ongoing investigations with semaglutide include the treatment of non-alcoholic fatty liver disease (NASH) and its use in an oral formulation for the treatment of T2D. In summary, rational design has led to the development of two long-acting GLP-1 analogs, liraglutide and semaglutide, that have made a vast contribution to the management of T2D in terms of improvements in glycemic control, body weight, blood pressure, lipids, beta-cell function, and CV outcomes. Furthermore, the development of an oral formulation for semaglutide may provide individuals with additional benefits in relation to treatment adherence. In addition to T2D, liraglutide is used in the treatment of obesity, while semaglutide is currently under investigation for use in obesity and NASH.

The glucagon-like peptide-1 receptor (GLP-1R) belongs to Family B1 of the seven-transmembrane G protein-coupled receptors, and its natural agonist ligand is the peptide hormone glucagon-like peptide-1 (GLP-1). GLP-1 is involved in glucose homeostasis, and activation of GLP-1R in the plasma membrane of pancreatic β-cells potentiates glucose-dependent insulin secretion. The N-terminal extracellular domain (nGLP-1R) is an important ligand binding domain that binds GLP-1 and the homologous peptide Exendin-4 with differential affinity. Exendin-4 has a C-terminal extension of nine amino acid residues known as the “Trp cage”, which is absent in GLP-1. The Trp cage was believed to interact with nGLP-1R and thereby explain the superior affinity of Exendin-4. However, the molecular details that govern ligand binding and specificity of nGLP-1R remain undefined. Here we report the crystal structure of human nGLP-1R in complex with the antagonist Exendin-4(9–39) solved by the multiwavelength anomalous dispersion method to 2.2Å resolution. The structure reveals that Exendin-4(9–39) is an amphipathic α-helix forming both hydrophobic and hydrophilic interactions with nGLP-1R. The Trp cage of Exendin-4 is not involved in binding to nGLP-1R. The hydrophobic binding site of nGLP-1R is defined by discontinuous segments including primarily a well defined α-helix in the N terminus of nGLP-1R and a loop between two antiparallel β-strands. The structure provides for the first time detailed molecular insight into ligand binding of the human GLP-1 receptor, an established target for treatment of type 2 diabetes. The glucagon-like peptide-1 receptor (GLP-1R) belongs to Family B1 of the seven-transmembrane G protein-coupled receptors, and its natural agonist ligand is the peptide hormone glucagon-like peptide-1 (GLP-1). GLP-1 is involved in glucose homeostasis, and activation of GLP-1R in the plasma membrane of pancreatic β-cells potentiates glucose-dependent insulin secretion. The N-terminal extracellular domain (nGLP-1R) is an important ligand binding domain that binds GLP-1 and the homologous peptide Exendin-4 with differential affinity. Exendin-4 has a C-terminal extension of nine amino acid residues known as the “Trp cage”, which is absent in GLP-1. The Trp cage was believed to interact with nGLP-1R and thereby explain the superior affinity of Exendin-4. However, the molecular details that govern ligand binding and specificity of nGLP-1R remain undefined. Here we report the crystal structure of human nGLP-1R in complex with the antagonist Exendin-4(9–39) solved by the multiwavelength anomalous dispersion method to 2.2Å resolution. The structure reveals that Exendin-4(9–39) is an amphipathic α-helix forming both hydrophobic and hydrophilic interactions with nGLP-1R. The Trp cage of Exendin-4 is not involved in binding to nGLP-1R. The hydrophobic binding site of nGLP-1R is defined by discontinuous segments including primarily a well defined α-helix in the N terminus of nGLP-1R and a loop between two antiparallel β-strands. The structure provides for the first time detailed molecular insight into ligand binding of the human GLP-1 receptor, an established target for treatment of type 2 diabetes. G protein-coupled receptors represent the largest protein family encoded by the human genome, and they are defined by the presence of seven transmembrane helices, an extracellular N terminus, ligand binding via the extracellular face, an intracellular C terminus, G protein coupling, and signaling via the intracellular face. Receptors of the B1 subfamily are specifically characterized by three conserved disulfide bonds in the N-terminal extracellular domain (Nt-domain) 2The abbreviations used are: Nt-domain, N-terminal extracellular domain; GIP, glucose-dependent insulinotropic polypeptide; PACAP, pituitary adenylate cyclase-activating polypeptide; CRF, corticotropin-releasing factor; Ex4, Exendin-4; TFE, trifluoroethanol; SeMet, selenomethionine; Fmoc, N-(9-fluorenyl)methoxycarbonyl. (1Perrin M.H. Fischer W.H. Kunitake K.S. Craig A.G. Koerber S.C. Cervini L.A. Rivier J.E. Groppe J.C. Greenwald J. Moller N.S. Vale W.W. J. Biol. Chem. 2001; 276: 31528-31534Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 2Lisenbee C.S. Dong M. Miller L.J. J. Biol. Chem. 2005; 280: 12330-12338Abstract Full Text Full Text PDF PubMed Scopus (32) Google Scholar, 3Grauschopf U. Lilie H. Honold K. Wozny M. Reusch D. Esswein A. Schafer W. Rucknagel K.P. Rudolph R. 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The current binding model is a two-step mechanism where initially the C-terminal part of the peptide ligand interacts with the Nt-domain of the receptor (6Lopez de Maturana R. Willshaw A. Kuntzsch A. Rudolph R. Donnelly D. J. Biol. Chem. 2003; 278: 10195-10200Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar, 7Dong M. Li Z. Zang M. Pinon D.I. Lybrand T.P. Miller L.J. J. Biol. Chem. 2003; 278: 48300-48312Abstract Full Text Full Text PDF PubMed Scopus (38) Google Scholar, 8Holtmann M.H. Hadac E.M. Miller L.J. J. Biol. Chem. 1995; 270: 14394-14398Abstract Full Text Full Text PDF PubMed Scopus (166) Google Scholar). In the second step, the N-terminal part of the ligand interacts with the core domain of the receptor (transmembrane helices and connecting loops), which leads to activation and signal transduction (9Solano R.M. Langer I. Perret J. Vertongen P. Juarranz M.G. Robberecht P. Waelbroeck M. J. Biol. Chem. 2001; 276: 1084-1088Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar, 10Runge S. Gram C. Brauner-Osborne H. Madsen K. Knudsen L.B. Wulff B.S. J. Biol. Chem. 2003; 278: 28005-28010Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, 11Dong M. Li Z. Pinon D.I. Lybrand T.P. Miller L.J. J. Biol. Chem. 2004; 279: 2894-2903Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar, 12Wittelsberger A. Corich M. Thomas B.E. Lee B.K. Barazza A. Czodrowski P. Mierke D.F. Chorev M. Rosenblatt M. Biochemistry. 2006; 45: 2027-2034Crossref PubMed Scopus (48) Google Scholar, 13Al-Sabah S. Donnelly D. FEBS Lett. 2003; 553: 342-346Crossref PubMed Scopus (36) Google Scholar, 14Lopez de Maturana R. Treece-Birch J. Abidi F. Findlay J.B. Donnelly D. Protein Pept. Lett. 2004; 11: 15-22Crossref PubMed Scopus (35) Google Scholar). More recently, it was proposed that the Nt-domain of the secretin receptor was involved in the activation mechanism, but such an endogenous agonist mechanism has not been confirmed for GLP-1R (15Dong M. Pinon D.I. Asmann Y.W. Miller L.J. Mol. Pharmacol. 2006; 70: 206-213Crossref PubMed Scopus (37) Google Scholar). The isolated soluble Nt-domains are able to bind their cognate ligands, although the affinity is often reduced compared with the full-length receptors (1Perrin M.H. Fischer W.H. Kunitake K.S. Craig A.G. Koerber S.C. Cervini L.A. Rivier J.E. Groppe J.C. Greenwald J. Moller N.S. Vale W.W. J. Biol. Chem. 2001; 276: 31528-31534Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar, 3Grauschopf U. Lilie H. Honold K. Wozny M. Reusch D. Esswein A. Schafer W. Rucknagel K.P. Rudolph R. Biochemistry. 2000; 39: 8878-8887Crossref PubMed Scopus (106) Google Scholar, 4Bazarsuren A. Grauschopf U. Wozny M. Reusch D. Hoffmann E. Schaefer W. Panzner S. Rudolph R. Biophys. Chem. 2002; 96: 305-318Crossref PubMed Scopus (74) Google Scholar, 6Lopez de Maturana R. Willshaw A. Kuntzsch A. Rudolph R. Donnelly D. J. Biol. Chem. 2003; 278: 10195-10200Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). The GLP-1R Nt-domain is important for both ligand binding and specificity, and it determines almost exclusively the ability of the full-length GLP-1R to discriminate between glucagon and GLP-1 (16Runge S. Wulff B.S. Madsen K. Brauner-Osborne H. Knudsen L.B. Br. J. Pharmacol. 2003; 138: 787-794Crossref PubMed Scopus (105) Google Scholar). This is physiologically important, given the essentially opposite effects of glucagon and GLP-1 on blood glucose. Detailed structural information exists for ligand-bound forms of the Nt-domain of the mouse CRF receptor 2β (nCRF-R2β), the human PACAP receptor (nPAC1), and the human GIP receptor (nGIPR) (17Parthier, C., Kleinschmidt, M., Neumann, P., Rudolph, R., Manhart, S., Schlenzig, D., Fanghanel, J., Rahfeld, J. U., Demuth, H. U., and Stubbs, M. T. (2007) Proc. Natl. Acad. Sci. U. S. A. 0706404104Google Scholar, 18Grace C.R. Perrin M.H. Gulyas J. DiGruccio M.R. Cantle J.P. Rivier J.E. Vale W.W. Riek R. Proc. Natl. Acad. Sci. U. S. A. 2007; 104: 4858-4863Crossref PubMed Scopus (122) Google Scholar, 19Sun C. Song D. A. M.R. Proc. Natl. Acad. Sci. U. S. A. 2007; 104: PubMed Scopus Google Scholar). The confirmed both the of a structural and the with the C-terminal part of their cognate the binding site and of was the binding site and of and The soluble nGLP-1R binds GLP-1 with affinity the full-length GLP-1R in that affinity binding of GLP-1 with the core domain of GLP-1R of and (6Lopez de Maturana R. Willshaw A. Kuntzsch A. Rudolph R. Donnelly D. J. Biol. Chem. 2003; 278: 10195-10200Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). the N-terminal part of GLP-1 is to interact with the first extracellular loop and the extracellular of transmembrane 2 of GLP-1R S. Gram C. Brauner-Osborne H. Madsen K. Knudsen L.B. Wulff B.S. J. Biol. Chem. 2003; 278: 28005-28010Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar, 13Al-Sabah S. Donnelly D. FEBS Lett. 2003; 553: 342-346Crossref PubMed Scopus (36) Google Scholar, 14Lopez de Maturana R. Treece-Birch J. Abidi F. Findlay J.B. Donnelly D. Protein Pept. Lett. 2004; 11: 15-22Crossref PubMed Scopus (35) Google Scholar). Exendin-4 is homologous to and it binds and GLP-1R with affinity and as GLP-1 R. T. H. M. J. J. Biol. Chem. Full Text PDF PubMed Google Scholar). In to affinity for with that of the full-length GLP-1R and (6Lopez de Maturana R. Willshaw A. Kuntzsch A. Rudolph R. Donnelly D. J. Biol. Chem. 2003; 278: 10195-10200Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). has a C-terminal extension of nine amino acid residues known as the Trp which is absent in GLP-1. The structure of in that the Trp cage the part of Ex4, forming the known R.M. Biol. 2002; PubMed Scopus Google Scholar, R.M. K.S. Biochemistry. 2001; PubMed Scopus Google Scholar). The Trp cage was to interact with thereby the superior affinity of compared with GLP-1 S. Donnelly D. Br. J. Pharmacol. 2003; PubMed Scopus Google Scholar). However, that the Trp cage a in receptor binding S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). the superior affinity of was by its superior in and by superior to residues in the C-terminal part of GLP-1 and S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). the of the Trp cage in receptor binding is not crystal Exendin-4(9–39) is a antagonist of both GLP-1 and receptor binding to its affinity with nGLP-1R of (6Lopez de Maturana R. Willshaw A. Kuntzsch A. Rudolph R. Donnelly D. J. Biol. Chem. 2003; 278: 10195-10200Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar, A. P. C. PubMed Google Scholar). the ligand binding of GLP-1R and Family B1 receptors in we solved the crystal structure of the complex between nGLP-1R and to resolution. The structure provides for the first time molecular details of the ligand binding of and it a structural of the differential affinity of nGLP-1R GLP-1 and Protein and Peptide nGLP-1R was as S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). N-terminal nGLP-1R was in isolated as in and to the and and a of reduced and nGLP-1R was by hydrophobic and The was by was as (16Runge S. Wulff B.S. Madsen K. Brauner-Osborne H. Knudsen L.B. Br. J. Pharmacol. 2003; 138: 787-794Crossref PubMed Scopus (105) Google Scholar). was by of residues the on Peptide was by in with of and with The was and as with a of and of nGLP-1R was to and with of nGLP-1R was by a in The complex was characterized by and Trp not The complex was to and by The was initially the and and to and to a of and they in in the and a crystal three the The and W. J. Scopus Google the to with the a and The two of the and C. E. P. Mol. Biol. 2006; Scholar). The was of and of of the structural model by A. R. Biol. PubMed Scopus Google Scholar) the with complex in the The of the structural model was and and P. K. Biol. 2004; PubMed Scopus Google PubMed Scopus Google and the Biol. PubMed Scopus Google Scholar). The model has residues in and residues in of the a of and a of and are in and structure are in the Protein in and in are for the the of of of of in a and nGLP-1R was in E. and as S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). a of the where and by The structure of that and on the of the α-helix of R.M. K.S. Biochemistry. 2001; PubMed Scopus Google Scholar). In of GLP-1 that two not important for receptor binding K. Knudsen L.B. J. Biol. Chem. Full Text PDF PubMed Google Scholar). binding to the with the as not The affinity of nGLP-1R and by The Trp of the protein a complex not where the ligand the for the The complex was in and the structure was solved by the multiwavelength anomalous dispersion method to the of the two in we and solved the structure of the complex with to by molecular nGLP-1R the structure as the model The two essentially for and of and are in and the the structure with the The of core structure of nGLP-1R is to that of and the three conserved disulfide two of antiparallel and conserved residues and of nGLP-1R and C.R. Perrin M.H. Gulyas J. DiGruccio M.R. Cantle J.P. Rivier J.E. Vale W.W. Riek R. Proc. Natl. Acad. Sci. U. S. A. 2007; 104: 4858-4863Crossref PubMed Scopus (122) Google Scholar, 19Sun C. Song D. A. M.R. Proc. Natl. Acad. Sci. U. S. A. 2007; 104: PubMed Scopus Google Scholar). The N terminus of nGLP-1R an α-helix to that of and the structure is by the disulfide and by interactions between the structure The α-helix is defined by residues and which forms a disulfide with on 2 The α-helix is by three residues the of loop The residues and the first antiparallel although the is and and are by a and The of interacts with the of the α-helix bonds with the of and The of the is by a with the of and by an with of The residues and with the second of antiparallel and are by a well defined loop that is important for ligand binding The disulfide between and the of and the of is the of and forms a disulfide with in the C-terminal part of nGLP-1R. The a with an of a loop was for residues and The human nGLP-1R seven Trp and of and by in of binding of the full-length of on binding activation A. R. PubMed Scopus Google Scholar). The of and is is not involved in ligand binding but to a structural by forming a well defined hydrophobic with and in the Nt-domain of Family B1 conserved of nGLP-1R is forming as for and although the molecular details are in crystal the of interacts via a with the of and with the of and In the and of interact with and the between and has a structural the that the of the the disulfide and is between the of and in a to The of and for ligand binding was by receptor A. R. PubMed Scopus Google Scholar, T.P. J. Biol. Chem. Full Text PDF PubMed Google Scholar). the of loop 2 a structurally important for the of the ligand binding site of nGLP-1R The of a hydrophobic by of the of of of of the disulfide and two residues of loop 2 and The and with is a well defined α-helix to and the residues that interact with nGLP-1R and the ligand residues are with and is The residues interact with nGLP-1R. is conserved in GLP-1 and Ex4, and it interacts with the of the α-helix of nGLP-1R via a with the of the first in the α-helix of nGLP-1R. The amphipathic of the hydrophobic interactions with nGLP-1R via of the α-helix and hydrophilic interactions via the of the The hydrophilic is defined by and of which and interact with nGLP-1R The of binds to the of of and the is for an with two is by and in an that the of in In a the of to interact with both the of of nGLP-1R and the of In the of the of the α-helix forms a with the of of nGLP-1R. the the C terminus of the ligand and of a on binding to that the interactions and S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). the structure that the of a with of nGLP-1R. The C-terminal of on the α-helix in a to the Trp cage of in R.M. K.S. Biochemistry. 2001; PubMed Scopus Google Scholar). However, the was for the C terminus of and we to a structure of part of the in the C terminus of to the Trp cage in where it was R.M. Biol. 2002; PubMed Scopus Google Scholar). that the Trp cage is not in the of and that not interact specifically with nGLP-1R. The hydrophobic of is defined by residues and and are by the hydrophobic with nGLP-1R and they are the residues of the ligand with the of is conserved in the glucagon peptide subfamily and and it interacts with and on the α-helix of nGLP-1R. The of and was by of GLP-1 and by of GLP-1R K. Knudsen L.B. J. Biol. Chem. Full Text PDF PubMed Google Scholar, A. R. PubMed Scopus Google Scholar). The of GLP-1 by the in the on the binding to the full-length of and reduced the affinity of GLP-1 although the was that of and are on and they are on the of the hydrophobic with nGLP-1R. is not involved in binding to and the of GLP-1 a of binding affinity the full-length GLP-1R K. Knudsen L.B. J. Biol. Chem. Full Text PDF PubMed Google Scholar). used the Trp to ligand binding of nGLP-1R S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). The that Trp residues in a hydrophobic binding of to nGLP-1R. The hydrophobic binding of nGLP-1R is by residues of discontinuous receptor and of the of of loop and the disulfide and are the hydrophobic with and by ligand The hydrophobic between nGLP-1R and an of the structure where are a hydrophobic The hydrophobic was a to the between and C.R. Perrin M.H. Gulyas J. DiGruccio M.R. Cantle J.P. Rivier J.E. Vale W.W. Riek R. Proc. Natl. Acad. Sci. U. S. A. 2007; 104: 4858-4863Crossref PubMed Scopus (122) Google Scholar). loop 2 of was and a well defined ligand binding C.R. Perrin M.H. Gulyas J. DiGruccio M.R. Cantle J.P. Rivier J.E. Vale W.W. Riek R. Proc. Natl. Acad. Sci. U. S. A. 2007; 104: 4858-4863Crossref PubMed Scopus (122) Google Scholar). of the ligand-bound nGLP-1R and that loop 2 of nGLP-1R is in the hydrophobic by a The conserved of nGLP-1R is important for binding mechanism and for the of loop In the complex with the of a hydrophobic on the of the hydrophobic ligand binding of loop 2 is between of and of nGLP-1R. The conserved a in ligand-bound and The of loop 2 the of of although it is in the ligand-bound The to which of its receptor binding is to However, is on the of the hydrophobic with nGLP-1R and it is the Trp cage is C-terminal of the of ligand-bound nGLP-1R S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). that the Trp cage the of to the that the Trp cage is in the complex between and nGLP-1R. residues on the α-helix of nGLP-1R a in crystal forming interactions and bonds with a receptor In the N-terminal part of a receptor and solved the structure of nGLP-1R to by molecular to nGLP-1R the structure as the model not The residues the N terminus of the ligand the as a the complex in with two in the the structure and the interactions not by the crystal and of GLP-1 and of in and in a The of the hydrophobic residues and of in is well defined and almost with their R.M. K.S. Biochemistry. 2001; PubMed Scopus Google Scholar). The to the structure and that of the Trp cage in However, the of the Trp cage in crystal structure that the Trp cage not bind to and is by the ligand binding of nGLP-1R S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). The hydrophobic residues and are conserved in GLP-1 and Ex4, and the of their binding to nGLP-1R and GLP-1R that the two the hydrophobic binding site of nGLP-1R. a between the of peptide in and their affinity for nGLP-1R S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). the differential affinity of and GLP-1 for nGLP-1R is by residues in the part of the in and in GLP-1. and of a by binding to nGLP-1R and by the of via and In on the hydrophobic of forms a hydrophobic with and of nGLP-1R. The residues in GLP-1 and explain its in as by and R.M. K.S. Biochemistry. 2001; PubMed Scopus Google Scholar, K.S. Chem. 2002; PubMed Scopus Google Scholar) and its affinity for nGLP-1R. In the structural of GLP-1 and in and the crystal structure of that the superior affinity of nGLP-1R for is by superior hydrophilic and hydrophobic interactions and by a superior of in the of receptor compared with GLP-1. This for the ability of to affinity for GLP-1R in to GLP-1 is a antagonist and is not C. H. A. L.A. J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The and the glucagon receptor Family The crystal of ligand-bound nGLP-1R and are for of residues of the receptors and the hydrophobic conserved residues of both the and the receptors (17Parthier, C., Kleinschmidt, M., Neumann, P., Rudolph, R., Manhart, S., Schlenzig, D., Fanghanel, J., Rahfeld, J. U., Demuth, H. U., and Stubbs, M. T. (2007) Proc. Natl. Acad. Sci. U. S. A. 0706404104Google Scholar). and of GLP-1R are exclusively conserved in the glucagon receptor and to specificity for the of the glucagon peptide and are the hydrophobic with and of and are not involved in ligand and they the binding site of the Nt-domain by interactions in to specifically the glucagon peptide The of and for ligand binding and specificity of GLP-1R to characterized by receptor the glucagon receptor residues specificity for the The ligand specificity of GLP-1R was in of glucagon by of the residues with the residues of the glucagon receptor Receptors Google Scholar). The ability of the to ligand specificity of GLP-1R is by the crystal structure where specifically of nGLP-1R is involved in the hydrophobic with The Family B1 that the two-step model for ligand binding of Family B1 receptors is the conserved N terminus of GLP-1 and binds to the core domain of which leads to receptor of GLP-1 of is by residues in the extracellular of transmembrane 2 of GLP-1R S. Gram C. Brauner-Osborne H. Madsen K. Knudsen L.B. Wulff B.S. J. Biol. Chem. 2003; 278: 28005-28010Abstract Full Text Full Text PDF PubMed Scopus (69) Google Scholar). of of the between residues that interact with the core domain of GLP-1R and residues that interact with nGLP-1R as S. S. J. Knudsen S.M. Madsen K. J. H. Rudolph R. Biochemistry. 2007; PubMed Scopus Google Scholar). The of nGLP-1R and in the that both the the core domain of of the secretin N terminus to the secretin receptor to with a model in which the N terminus of both the ligand and the receptor are in with the core domain of the receptor M. Pinon D.I. Miller L.J. Mol. 2005; PubMed Scopus Google Scholar). the superior affinity of for nGLP-1R is not into a superior the full-length GLP-1R compared with GLP-1. ligand binding of GLP-1R is complex that of the isolated and the second binding of GLP-1R for the affinity of nGLP-1R for GLP-1 to of the human GLP-1R was as a of antagonist binding C. M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Google Scholar). The binding of GLP-1R and reduced the of a is in the N-terminal part of the α-helix of on the opposite site of but the hydrophobic binding of the antagonist to of nGLP-1R receptor activation by with the hydrophobic by the between the receptor core domain and the α-helix of the In both binding of the antagonist to of nGLP-1R the N terminus of GLP-1 and into a for receptor in the However, it is the antagonist binds to and the of nGLP-1R with to the core domain is not of the between the ligand-bound of Family B1 receptor Nt-domains is the binding site and of the ligand (17Parthier, C., Kleinschmidt, M., Neumann, P., Rudolph, R., Manhart, S., Schlenzig, D., Fanghanel, J., Rahfeld, J. U., Demuth, H. U., and Stubbs, M. T. (2007) Proc. Natl. Acad. Sci. U. S. A. 0706404104Google Scholar, 18Grace C.R. Perrin M.H. Gulyas J. DiGruccio M.R. Cantle J.P. Rivier J.E. Vale W.W. Riek R. Proc. Natl. Acad. Sci. U. S. A. 2007; 104: 4858-4863Crossref PubMed Scopus (122) Google Scholar, 19Sun C. Song D. A. M.R. Proc. Natl. Acad. Sci. U. S. A. 2007; 104: PubMed Scopus Google Scholar). The binding site of GIP, and is on the of the Nt-domain, and the ligand is the However, the of and GIP is to they interact with the α-helix of their binds to a site of and has its compared with the The N terminus of Ex4, GIP, CRF, and PACAP is important for receptor and it is to interact with the receptor core the of to the receptor core domain membrane the of and The crystal structure provides detailed molecular information the first of peptide ligand binding of the human GLP-1 the for treatment of type 2 the GLP-1 of the full-length receptor is to the of the Nt-domains and the of receptor and to the activation and for with and S. for and the the for with