title: Three-dimensional structure of a gamma-carboxyglutamic acid-containing conotoxin, conantokin G, from the marine snail Conus geographus: the metal-free conformer.
abstract: Conantokin G is a gamma-carboxyglutamic acid-containing conotoxin from the venom of the marine cone snail Conus geographus. The 17-residue peptide, which contains five gamma-carboxyglutamic acid (Gla) residues and an amidated C-terminal asparagine amide, was synthesized chemically in a form identical to the natural conantokin G. To gain insight into the role of gamma-carboxyglutamic acid in the structure of this peptide, we determined the three-dimensional structure of conantokin G by 1H NMR and compared its structure to other conotoxins and to the gamma-carboxyglutamic acid-containing regions of the vitamin K-dependent blood-clotting proteins. Complete resonance assignments were made by two-dimensional 1H NMR spectroscopy in the absence of metal ions. NOE cross-peaks d(alphaN), d(NN), and d(betaN) provided interproton distance information, and vicinal spin-spin coupling constants 3J(HN alpha) were used to calculate phi torsion angles. Distance geometry and simulated annealing methods were used to derive 20 convergent structures from a set of 227 interproton distance restraints and 13 torsion angle measurements. The backbone rmsd to the geometric average for 20 final structures is 0.8 +/- 0.1 A. Conantokin G consists of a structured region commencing at Gla 3 and extending through arginine 13. This structure includes a partial loop centered around Gla 3 and Gla 4, a distorted type I turn between glutamine 6 and glutamine 9, and two type I turns involving Gla 10, leucine 11, and isoleucine 12 and arginine 13. Together, these two turns define approximately 1.6 turns of a distorted 3(10) helix. The observed structure possesses structural elements similar to those seen in the disulfide-linked conotoxins.
authors.affiliation: New England Medical Center, and Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Rigby
authors.forename: J D
authors.initials: JD
authors.lastname: Baleja
authors.forename: B C
authors.initials: BC
authors.lastname: Furie
authors.forename: B
authors.initials: B
authors.lastname: Furie
mesh_terms: D015055:1-Carboxyglutamic Acid / Q000737:chemistry*; D000818:Animals; D020916:Conotoxins; D018691:Excitatory Amino Acid Antagonists / Q000737:chemistry* / Q000378:metabolism; D008670:Metals / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008978:Mollusk Venoms / Q000737:chemistry* / Q000378:metabolism; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000378:metabolism; D012908:Snails; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013329:Structure-Activity Relationship
chemical_list: D020916:Conotoxins; D018691:Excitatory Amino Acid Antagonists; D008670:Metals; D008978:Mollusk Venoms; D010456:Peptides, Cyclic; D011956:Receptors, Cell Surface; C106613:conantokin receptor, Mollusk; D015055:1-Carboxyglutamic Acid; C055407:conotoxin GV