title: Role of gamma-carboxyglutamic acid in the calcium-induced structural transition of conantokin G, a conotoxin from the marine snail Conus geographus.
abstract: Conantokin G is a gamma-carboxyglutamic acid- (Gla-) containing conotoxin isolated from the venom of the marine cone snail Conus geographus. This 17-residue polypeptide, which contains five gamma-carboxyglutamic acid residues, is a N-methyl-d-aspartate- (NMDA-) type glutamate receptor antagonist. To investigate the role of gamma-carboxyglutamic acid in the calcium-induced structural transition of conantokin G, we determined the three-dimensional structure of the conantokin G/Ca2+ complex by two-dimensional 1H NMR spectroscopy and compared it to the high-resolution structure of conantokin G in the absence of metal ions [Rigby et al. (1997) Biochemistry 36, 6906]. Complete resonance assignments were made by two dimensional 1H NMR spectroscopy at pH 5.6 in the presence of saturating amounts of Ca2+. Distance geometry and simulated annealing methods were used to derive 23 convergent structures from a set of 302 interproton distance restraints and two torsion angle measurements. A high-resolution structure, with the backbone root mean square deviation to the geometric average of the 23 structures of 0.6 +/- 0.1 A, contains a linear alpha-helix from Gla 3 to Lys 15. Gla residues 3, 7, 10, and 14 are aligned in a linear array on one face of the helix. A genetic algorithm was applied to determine the calcium positions in conantokin G, and the conantokin G/Ca2+ complex refined by molecular simulation. Upon binding of Ca2+ to gamma-carboxyglutamic acid, conantokin G undergoes a conformational transition from a distorted curvilinear 310 helix to a linear alpha-helix. Occupancy of the metal binding sites, defined by gamma-carboxyglutamic acids, results in formation of a calcium-carboxylate network that linearizes the helix and exposes the hydrophobic amino acids on the opposite face of the helix.
authors.affiliation: Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Rigby
authors.forename: J D
authors.initials: JD
authors.lastname: Baleja
authors.forename: L
authors.initials: L
authors.lastname: Li
authors.forename: L G
authors.initials: LG
authors.lastname: Pedersen
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 / Q000378:metabolism*; D000465:Algorithms; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D003198:Computer Simulation; D020916:Conotoxins; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008978:Mollusk Venoms / Q000737:chemistry* / Q000378:metabolism; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D012908:Snails / Q000737:chemistry
chemical_list: D020916:Conotoxins; D008978:Mollusk Venoms; D010456:Peptides, Cyclic; D016194:Receptors, N-Methyl-D-Aspartate; D015055:1-Carboxyglutamic Acid; C055407:conotoxin GV; D002118:Calcium