title: Lactam constraints provide insights into the receptor-bound conformation of secretin and stabilize a receptor antagonist.
abstract: The natural ligands for family B G protein-coupled receptors are moderate-length linear peptides having diffuse pharmacophores. The amino-terminal regions of these ligands are critical for biological activity, with their amino-terminal truncation leading to production of orthosteric antagonists. The carboxyl-terminal regions of these peptides are thought to occupy a ligand-binding cleft within the disulfide-bonded amino-terminal domains of these receptors, with the peptides in amphipathic helical conformations. In this work, we have characterized the binding and activity of a series of 11 truncated and lactam-constrained secretin(5-27) analogues at the prototypic member of this family, the secretin receptor. One peptide in this series with lactam connecting residues 16 and 20 [c[E(16),K(20)][Y(10)]sec(5-27)] improved the binding affinity of its unconstrained parental peptide 22-fold while retaining the absence of endogenous biological activity and competitive antagonist characteristics. Homology modeling with molecular mechanics and molecular dynamics simulations established that this constrained peptide occupies the ligand-binding cleft in an orientation similar to that of natural full-length secretin and provided insights into why this peptide was more effective than other truncated conformationally constrained peptides in the series. This lactam bridge is believed to stabilize an extended α-helical conformation of this peptide while in solution and not to interfere with critical residue-residue approximations while docked to the receptor.
authors.affiliation: Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Scottsdale, Arizona 85259, USA.
authors.forename: Maoqing
authors.initials: M
authors.lastname: Dong
authors.forename: Jerez A
authors.initials: JA
authors.lastname: Te
authors.forename: Xiequn
authors.initials: X
authors.lastname: Xu
authors.forename: Jinhui
authors.initials: J
authors.lastname: Wang
authors.forename: Delia I
authors.initials: DI
authors.lastname: Pinon
authors.forename: Laura
authors.initials: L
authors.lastname: Storjohann
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Bordner
authors.forename: Laurence J
authors.initials: LJ
authors.lastname: Miller
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D066298:In Vitro Techniques; D007769:Lactams / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D011487:Protein Conformation; D055550:Protein Stability; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011964:Receptors, Gastrointestinal Hormone / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012633:Secretin / Q000031:analogs & derivatives / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D007769:Lactams; D008024:Ligands; D046912:Multiprotein Complexes; D010455:Peptides; D043562:Receptors, G-Protein-Coupled; D011964:Receptors, Gastrointestinal Hormone; D011994:Recombinant Proteins; C029937:secretin receptor; D012633:Secretin