title: Evolution of constrained gonadotropin-releasing hormone ligand conformation and receptor selectivity.
abstract: Gonadotropin-releasing hormone (GnRH) is the central regulator of reproduction in vertebrates. GnRHs have recently been identified in protochordates and retain the conserved N- and C-terminal domains involved in receptor binding and activation. GnRHs of the jawed vertebrates have a central achiral amino acid (glycine) that favors a type II' beta-turn such that the N- and C-terminal domains are closely apposed in binding the GnRH receptor. However, protochordate GnRHs have a chiral amino acid in this position, suggesting that they bind their receptors in a more extended form. We demonstrate here that a protochordate GnRH receptor does not distinguish GnRHs with achiral or chiral amino acids, whereas GnRH receptors of jawed vertebrates are highly selective for GnRHs with the central achiral glycine. The poor activity of the protochordate GnRH was increased >10-fold at vertebrate receptors by replacement of the chiral amino acid with glycine or a d-amino acid, which favor the type II' beta-turn. Structural analysis of the GnRHs using ion mobility-mass spectrometry and molecular modeling showed a greater propensity for a type II' beta-turn in GnRHs with glycine or a d-amino acid, which correlates with binding affinity at vertebrate receptors. These findings indicate that the substitution of glycine for a chiral amino acid in GnRH during evolution allows a more constrained conformation for receptor binding and that this subtle single amino acid substitution in a site remote from the ligand functional domains has marked effects on its structure and activity.
authors.affiliation: School of Chemistry, The University of Edinburgh, Edinburgh EH9 3JJ, United Kingdom.
authors.forename: Perdita E
authors.initials: PE
authors.lastname: Barran
authors.forename: Roger W
authors.initials: RW
authors.lastname: Roeske
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Pawson
authors.forename: Robin
authors.initials: R
authors.lastname: Sellar
authors.forename: Michael T
authors.initials: MT
authors.lastname: Bowers
authors.forename: Kevin
authors.initials: K
authors.lastname: Morgan
authors.forename: Zhi-Liang
authors.initials: ZL
authors.lastname: Lu
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Tsuda
authors.forename: Takehiro
authors.initials: T
authors.lastname: Kusakabe
authors.forename: Robert P
authors.initials: RP
authors.lastname: Millar
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002397:Catfishes; D002460:Cell Line; D002645:Chickens; D002522:Chlorocebus aethiops; D002938:Ciona intestinalis; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D005998:Glycine / Q000737:chemistry; D007987:Gonadotropin-Releasing Hormone / Q000737:chemistry*; D006801:Humans; D020128:Inhibitory Concentration 50; D007295:Inositol Phosphates / Q000737:chemistry; D008024:Ligands; D013058:Mass Spectrometry; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011966:Receptors, LHRH / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014162:Transfection
chemical_list: D007295:Inositol Phosphates; D008024:Ligands; D010455:Peptides; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D005998:Glycine