title: Determination of the solution structures of conantokin-G and conantokin-T by CD and NMR spectroscopy.
abstract: Conantokin-G and conantokin-T are two paralytic polypeptide toxins originally isolated from the venom of the fish-hunting cone snails of the genus Conus. Conantokin-G and conantokin-T are the only naturally occurring peptidic compounds which possess N-methyl-D-aspartate receptor antagonist activity, produced by a selective non-competitive antagonism of polyamine responses. They are also structurally unusual in that they contain a disproportionately large number of acid labile post-translational gamma-carboxyglutamic acid (Gla) residues. Although no precise structural information has previously been published for these peptides, early spectroscopic measurements have indicated that both conantokin-G and conantokin-T form alpha-helical structures, although there is some debate whether the presence of calcium ions is required for these peptides to adopt this fold. We now report a detailed structural study of synthetic conantokin-G and conantokin-T in a range of solution conditions using CD and 1H NMR spectroscopy. The three-dimensional structures of conantokin-T and conantokin-G were calculated from 1H NMR-derived distance and dihedral restraints. Both conantokins were found to contain a mixture of alpha- and 310 helix, that give rise to curved and straight helical conformers. Conantokin-G requires the presence of divalent cations (Zn2+, Ca2+, Cu2+, or Mg2+) to form a stable alpha-helix, while conantokin-T adopts a stable alpha-helical structure in aqueous conditions, in the presence or absence of divalent cations (Zn2+, Ca2+, Cu2+, or Mg2+).
authors.affiliation: The Centre for Drug Design and Development, The University of Queensland, Brisbane, Qld 4072, Australia.
authors.forename: N
authors.initials: N
authors.lastname: Skjaerbaek
authors.forename: K J
authors.initials: KJ
authors.lastname: Nielsen
authors.forename: R J
authors.initials: RJ
authors.lastname: Lewis
authors.forename: P
authors.initials: P
authors.lastname: Alewood
authors.forename: D J
authors.initials: DJ
authors.lastname: Craik
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D020916:Conotoxins; D018691:Excitatory Amino Acid Antagonists / Q000737:chemistry*; D036341:Intercellular Signaling Peptides and Proteins; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D008978:Mollusk Venoms / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D012908:Snails
chemical_list: D020916:Conotoxins; D018691:Excitatory Amino Acid Antagonists; D036341:Intercellular Signaling Peptides and Proteins; D008978:Mollusk Venoms; D010455:Peptides; D010456:Peptides, Cyclic; C063571:conantokin-T; C055407:conotoxin GV