Two distinct structures of α‐conotoxin GI in aqueous solution

Abstract

The detailed analysis of conformational space of A-conotoxin GI in aqueous solution has been performed on the basis of two-dimensional NMR spectroscopy data using multiconformational approach. As the result, two topologically distinct interconvertible sets of GI conformations (populations of 78% and 22%) have been found. A common feature of the two sets is the Asn4-Cys7 β-turn. The Gly8 to Tyr11 region has a structure of right-handed helical turn in the major set and two sequential bends in the minor one. N-terminus and C-terminus also have different orientations, anti-parallel in the major conformational set and parallel in the minor one. An average pairwise rmsd for backbone heavy atoms is 0.56 Å in the major set, 0.23 Å in the minor, and 1.85 Å between the structures of the two sets. The X-ray structure of GI [Guddat, L. W., Martin, J. A., Shan, L., Edmundson, A. B. & Gray, W. R. (1996) Biochemistry 35, 11 329Ϫ11 335] has the same folding pattern as the major NMR set, the average backbone rmsd between the two structures being 0.77 Å .Keywords : conotoxin ; nicotinic acetylcholine receptor; NMR; conformational analysis.The venom of marine snails of the Conus genus contains structure, dynamics, and their relationship with the biological function of peptides. However, in practice high-resolution X-ray oligopeptide neurotoxins which are sophisticated tools for studying a wide range of receptors and ion channels : A-conotoxins structures of small flexible peptides are often biased by crystal packing forces and may differ from a biologically active conforblock nicotinic acetylcholine receptors (nAChR), µ-conotoxins and ω-conotoxins act on voltage-gated sodium and calcium mation. In turn, NMR spectroscopy faces technical difficulties when dealing with flexible molecules. Quite often it is stated channels, respectively, while the targets of the contatokins are the N-methyl-D-aspartate receptors (see review [1]). The most that a number of different conformations in fast exchange are present in solution, among which one can expect a biologically numerous family is that of A-conotoxins consisting of over 10 members whose primary structure has been established and bio-active conformation. Several techniques were proposed for analysis of NMR data on flexible molecules [11Ϫ18], but the logical activity analysed. The efficiency of the interaction between nAChR and A-conotoxins depends on the species and sub-problem is still far from being solved. Here we introduce a new approach for the analysis of NMR data of flexible peptides and type of the nAChR. Most of A-conotoxins block the neuromuscular nAChR. However, several recently discovered A-conotox-show that A-conotoxin GI in aqueous solution is represented by two topologically distinct sets of interconvertible conformations. ins act on neuronal nAChR [2]. Besides the above-mentioned species-selectivities and subtype-selectivities, recent data describe the affinity and binding selectivity to the Torpedo membranes or to AChR in the mouse cell line for the naturally occur-MA...

Solution Conformation of α-Conotoxin EI, a Neuromuscular Toxin Specific for the α1/δ Subunit Interface of Torpedo Nicotinic Acetylcholine Receptor

“…Because of trans-cis isomerization of prolines, minor peaks originating from a cis-conformer were noted. Similar cis conformers have been observed in other ␣-/␣A-conotoxins as well (13,27,34,41). Detailed analyses of NMR data and structure calculation have been carried out for the trans-isomer.…”

Hydrophobic Pairwise Interactions Stabilize α-Conotoxin MI in the Muscle Acetylcholine Receptor Binding Site

“…3 is that of the major conformation, but the structure of the minor conformation has not been reported. However, for CTx GI, which has a similar pharmacological fingerprint to CTx MI, atomic coordinates of both major and minor conformations have been reported (31). Comparison of all reported structures of CTx GI indicates that the major conformers of CTx MI and GI are structurally similar (31)(32)(33)(34).…”

“…However, for CTx GI, which has a similar pharmacological fingerprint to CTx MI, atomic coordinates of both major and minor conformations have been reported (31). Comparison of all reported structures of CTx GI indicates that the major conformers of CTx MI and GI are structurally similar (31)(32)(33)(34). If the two conformers for CTx GI are comparable to those for CTx MI, we can ask whether any of the four bioactive residues change positions between major and minor conformations.…”

“…Side chains of Pro-6, Ala-7, and Gly-9 have similar coordinates in CTx MI and GI and change very little between major and minor conformations. However, to achieve the minor conformation of CTx GI, the peptide backbone between glycine 9 and serine 13 twists so the side chain of Tyr-12 moves out of the hydrophobic pocket to protrude on the opposite side of the toxin (31,32). If the minor conformer is the one bound to the AChR, the ␣ and ␦ subunits would be estimated to be farther apart than if the major conformer is bound.…”

Characterization of a novel α4/4-conotoxin, Qc1.2, from vermivorous <italic>Conus quercinus</italic>

“…Previous results suggested that some a3/5-conotoxins also exhibit asymmetric elution peaks on HPLC following oxidation, and have two conformations in aqueous condition [13,[21][22][23], which differ in the second Cys loop and peptide termini region [23]. It would be difficult to determine which conformer is more favorable for peptide activity on nAChRs.…”