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Volume 272, Number 4, Issue of January 24, 1997 pp. 2291-2299
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

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

(Received for publication, June 18, 1996, and in revised form, September 5, 1996)

From The Centre for Drug Design and Development, The University of Queensland, Brisbane, Qld 4072, Australia

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

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