PDBsum entry 2bc8

Toxin

PDB id: 2bc8

Contents

Protein chain

12 a.a.

PDB id:

2bc8

Name:

Toxin

Title:

[Sec2,3,8,12]-imi

Structure:

Alpha-conotoxin imi. Chain: a. Engineered: yes

Source:

Synthetic: yes. Other_details: solid phase peptide synthesis

NMR struc:

20 models

Authors:

C.J.Armishaw

Key ref:

C.J.Armishaw et al. (2006). Alpha-selenoconotoxins, a new class of potent alpha7 neuronal nicotinic receptor antagonists. J Biol Chem, 281, 14136-14143. PubMed id: 16500898 DOI: 10.1074/jbc.M512419200

Date:

18-Oct-05 Release date: 14-Mar-06

Protein chain

P50983  (CA1_CONIM) -  Alpha-conotoxin ImI (Fragment) from Conus imperialis

Seq: 17 a.a.

Struc: 12 a.a.*

* PDB and UniProt seqs differ at 4 residue positions (black crosses)

Enzyme reactions

• Enzyme class: E.C.?

DOI no: 10.1074/jbc.M512419200

J Biol Chem 281:14136-14143 (2006)

PubMed id: 16500898

Alpha-selenoconotoxins, a new class of potent alpha7 neuronal nicotinic receptor antagonists.

C.J.Armishaw, N.L.Daly, S.T.Nevin, D.J.Adams, D.J.Craik, P.F.Alewood.

ABSTRACT

Disulfide bonds are important structural motifs that play an essential role in maintaining the conformational stability of many bioactive peptides. Of particular importance are the conotoxins, which selectively target a wide range of ion channels that are implicated in numerous disease states. Despite the enormous potential of conotoxins as therapeutics, their multiple disulfide bond frameworks are inherently unstable under reducing conditions. Reduction or scrambling by thiol-containing molecules such as glutathione or serum albumin in intracellular or extracellular environments such as blood plasma can decrease their effectiveness as drugs. To address this issue, we describe a new class of selenoconotoxins where cysteine residues are replaced by selenocysteine to form isosteric and nonreducible diselenide bonds. Three isoforms of alpha-conotoxin ImI were synthesized by t-butoxycarbonyl chemistry with systematic replacement of one ([Sec(2,8)]ImI or [Sec(3,12)]ImI), or both ([Sec(2,3,8,12)]ImI) disulfide bonds with a diselenide bond. Each analogue demonstrated remarkable stability to reduction or scrambling under a range of chemical and biological reducing conditions. Three-dimensional structural characterization by NMR and CD spectroscopy indicates conformational preferences that are very similar to those of native ImI, suggesting fully isomorphic structures. Additionally, full bioactivity was retained at the alpha7 nicotinic acetylcholine receptor, with each selenoanalogue exhibiting a dose-response curve that overlaps with wild-type ImI, thus further supporting an isomorphic structure. These results demonstrate that selenoconotoxins can be used as highly stable scaffolds for the design of new drugs.

Selected figure(s)

Figure 1.
α-Selenoconotoxin analogues of ImI. Connectivity between cysteine/selenocysteine residues is indicated.

Figure 3.
Structural studies of α-selenoconotoxin ImI analogues. Circular dichroism spectra (A) and a comparison of the NH (B) and Hα (C) backbone chemical shifts are shown. WT ImI shifts from Gehrmann et al. (24) were used. Secondary chemical shifts were calculated by subtracting random coil values (54) from the observed chemical shifts. •, WT ImI; ○, [Sec^2,8]ImI; ▴, [Sec^3,12]ImI; ▵, [Sec^2,3,8,12]ImI. D, overlay of the backbones (N, Cα, and CO atoms) and of the disulfide and diselenide bonds of the 20 minimum energy conformers representing the [Sec^2,8]ImI and [Sec^2,3,8,12]ImI NMR-derived structures. Disulfide bonds are shown in red, and diselenide bonds are shown in yellow. E, ribbon representations of [Sec^2,8]ImI and [Sec^2,3,8,12]ImI. WT ImI is shown for comparison (25). F, overlays of the minimum energy structures of [Sec^2,8]ImI and [Sec^2,3,8,12]ImI with WT ImI (left and middle, respectively) and overlay of [Sec^2,8]ImI on [Sec^2,3,8,12]ImI (right).

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2006, 281, 14136-14143) copyright 2006.

Figures were selected by the author.