title: Structure of a receptor-binding fragment from human luteinizing hormone beta-subunit determined by [1H]- and [15N]nuclear magnetic resonance spectroscopy.
abstract: The structure of the glycoprotein hormones (LH, CG, FSH, and TSH) and their mechanism of receptor recognition are problems of long-standing interest and speculation. Here we describe the two-dimensional [1H]nuclear magnetic resonance ([1H]NMR) analysis of a linear peptide model for the intercysteine sequence (38-57) from the beta-subunit of human (h) LH. This sequence contains functional determinants for receptor binding and postreceptor activation and is predicted by computer-based modeling to fold as a compact minidomain containing a central amphipathic helix. To test this prediction, an Arg-extended disulfide-free (38-57) analog of enhanced solubility was prepared for complementary circular-dichroic and two-dimensional NMR studies. The linear peptide retains ovarian membrane receptor-binding activity. Although the peptide is not highly structured in aqueous solution, circular-dichroic analysis shows partial alpha-helix formation in a lipophilic medium (50% trifluoroethanol). Complete sequential assignment is obtained in 50% trifluoroethanol based on homonuclear and [15N]edited heteronuclear NMR methods. alpha-Helix-related (i,i + 3) connectivities are observed by nuclear-Overhauser effect spectroscopy that define an amphipathic alpha-helical segment (residues 41-48). Additional long range nuclear-Overhauser effects are observed in the C-terminal region that are consistent with beta-turns involving one or more proline residues; these may serve to reverse the direction of the peptide chain. A nuclear-Overhauser effect contact is identified between residues 38 and 55 at opposite ends of the linear sequence, suggesting that a loop configuration is significantly populated in this solvent system. These results, taken together, characterize elements of ordered structure in the 38-57 peptide, which appear to be distinguishing features of hLH (and the homologous region of hCG). We propose that the structure of this peptide provides a model for the structure of the corresponding region of native hLH in the hormone-receptor complex.
authors.affiliation: Department of Medicine, Massachusetts General Hospital, Boston 02114.
authors.forename: H T
authors.initials: HT
authors.lastname: Keutmann
authors.forename: Q X
authors.initials: QX
authors.lastname: Hua
authors.forename: M A
authors.initials: MA
authors.lastname: Weiss
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D006801:Humans; D006859:Hydrogen; D007986:Luteinizing Hormone / Q000737:chemistry* / Q000235:genetics; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009587:Nitrogen Isotopes; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry; D011487:Protein Conformation; D012045:Regulatory Sequences, Nucleic Acid
chemical_list: D009587:Nitrogen Isotopes; D010446:Peptide Fragments; D006859:Hydrogen; D007986:Luteinizing Hormone