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PDBsum entry 2bc8
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References listed in PDB file
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Key reference
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Title
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Alpha-Selenoconotoxins, A new class of potent alpha7 neuronal nicotinic receptor antagonists.
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Authors
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C.J.Armishaw,
N.L.Daly,
S.T.Nevin,
D.J.Adams,
D.J.Craik,
P.F.Alewood.
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Ref.
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J Biol Chem, 2006,
281,
14136-14143.
[DOI no: ]
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PubMed id
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Abstract
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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.
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Figure 1.
α-Selenoconotoxin analogues of ImI. Connectivity between
cysteine/selenocysteine residues is indicated.
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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).
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2006,
281,
14136-14143)
copyright 2006.
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