Determination of the Solution Structures of Conantokin-G and Conantokin-T by CD and NMR Spectroscopy

• Published in: The Journal of biological chemistry 1997-01, Vol.272 (4), p.2291-2299
• Main Authors: Skjærbæk, Niels, Nielsen, Katherine J., Lewis, Richard J., Alewood, Paul, Craik, David J.
• Format: Article
• Language: English
• Subjects: Animals; Chromatography, High Pressure Liquid; Circular Dichroism; Conotoxins; Conus; Excitatory Amino Acid Antagonists - chemistry; Intercellular Signaling Peptides and Proteins; Magnetic Resonance Spectroscopy; Marine; Molecular Sequence Data; Mollusk Venoms - chemistry; Peptides - chemistry; Peptides, Cyclic - chemistry; Protein Conformation; Snails
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.4.2291

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 γ-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 α-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 α- 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 α-helix, while conantokin-T adopts a stable α-helical structure in aqueous conditions, in the presence or absence of divalent cations (Zn2+, Ca2+, Cu2+, or Mg2+).