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 ␥-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 1 H NMR spectroscopy. The three-dimensional structures of conantokin-T and conantokin-G were calculated from 1 H NMR-derived distance and dihedral restraints. Both conantokins were found to contain a mixture of ␣-and 3 10 helix, that give rise to curved and straight helical conformers.

Antagonistic action on NMDA/GluN2B mediated currents of two peptides that were conantokin-G structure-based designed

“…Figure 6 shows the predicted structure for EAR18 and EAR16 and the one reported for conantokin-G [47, 48]. While conantokin-G adopts a helical conformation in more than 70% of its sequence [47, 48], EAR18 and EAR16 adopt a helical conformation in 50% (EAR18) or less (EAR16) of their sequence. The high level of helical conformation in conantokin-G is due to the presence of Gla, which coordinates binding of 4 calcium ions [48–50].…”

“…While conantokin-G adopts a helical conformation in more than 70% of its sequence [47, 48], EAR18 and EAR16 adopt a helical conformation in 50% (EAR18) or less (EAR16) of their sequence. The high level of helical conformation in conantokin-G is due to the presence of Gla, which coordinates binding of 4 calcium ions [48–50]. The decrease in the proportion of helical conformation will increase the molecular flexibility of EAR18 and EAR16 and this may contribute to the observed high reversibility of EAR16 and EAR18 (present study).…”

“…6Schematic representation (backbone ribbons) of peptides. The predicted structures for EAR16 ( a , c ) and EAR18 ( b , d ), and the NMR reported structure for Con-G ( e ) (PDB: 1ONU [48]) are shown. The 3D predicted structure for EAR16 and EAR18 was performed using a hydrophilic environment, both peptides EAR16 and EAR18 shown a non-compact helical conformation compared with Con-G.…”

In the picture: disulfide-poor conopeptides, a class of pharmacologically interesting compounds

“…CGU = Gla: γ-carboxyglutamic acid. Conantokins adopt an α-helical solution structure in the presence of divalent cations in which charged carboxyl groups of the Gla residues are positioned along one face of the helix and hydrophobic residues are on the opposite face [83]. Figures were created with Pymol [82] (PDB 1ONT and 1ONU for Con-T and Con-G, respectively) …”

From Toxins Targeting Ligand Gated Ion Channels to Therapeutic Molecules

“…The conantokins (G, L, R and T) form a class of peptides that inhibit competitively NMDA receptors [79,80]. Interestingly conantokins possess a large number of γ-carboxyglutamic acid residues (Figure 7) [81]. One of the γ−carboxyglutamic acid residues is thought to participate in the selectivity of conantokin G [82].…”