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PDBsum entry 1bcg
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Excitatory neurotoxin
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PDB id
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1bcg
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References listed in PDB file
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Key reference
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Title
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An excitatory scorpion toxin with a distinctive feature: an additional alpha helix at the c terminus and its implications for interaction with insect sodium channels.
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Authors
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D.A.Oren,
O.Froy,
E.Amit,
N.Kleinberger-Doron,
M.Gurevitz,
B.Shaanan.
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Ref.
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Structure, 1998,
6,
1095-1103.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: Scorpion neurotoxins, which bind and modulate sodium channels, have
been divided into two groups, the alpha and beta toxins, according to their
activities. The beta-toxin class includes the groups of excitatory and
depressant toxins, which differ in their mode of action and are highly specific
against insects. The three-dimensional structures of several alpha and beta
toxins have been determined at high resolution, but no detailed 3D structure of
an excitatory toxin has been presented so far. RESULTS: The crystal structure of
an anti-insect excitatory toxin from the scorpion Buthotus judaicus, Bj-xtrIT,
has been determined at 2.1 A resolution and refined to an R factor of 0.209. The
first 59 residues form a closely packed module, structurally similar to the
conserved alpha and beta toxins ('long toxins') affecting sodium channels. The
last 17 residues form a C-terminal extension not previously seen in scorpion
toxins. It comprises a short alpha helix anchored to the N-terminal module by a
disulfide bridge and is followed by a highly mobile stretch of seven residues,
of which only four are seen in the electron-density map. This mobile peptide
covers part of a conserved hydrophobic surface that is thought to be essential
for interaction with the channel in several long toxins. CONCLUSIONS:
Replacement of the last seven residues by a single glycine abolishes the
activity of Bj-xtrIT, strongly suggesting that these residues are intimately
involved in the interaction with the channel. Taken together with the partial
shielding of the conserved hydrophobic surface and the proximity of the C
terminus to an adjacent surface rich in charged residues, it seems likely that
the bioactive surface of Bj-xtrIT is formed by residues surrounding the C
terminus. The 3D structure and a recently developed expression system for
Bj-xtrIT pave the way for identifying the structural determinants involved in
the bioactivity and anti-insect specificity of excitatory toxins.
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Figure 4.
Figure 4. Overall structures of (a) CsE-v3, (b) Bj-xtrIT
and (c) AaHII, viewed in the same orientation. Structural
elements of Bj-xtrIT are in the same color scheme as in Figure
2. On each panel, the disulfide bridges are numbered 1-3 for
conserved and, 4 for nonconserved (see text and Figure 2). The
figure was prepared using the program MOLSCRIPT [45].
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The above figure is
reprinted
by permission from Cell Press:
Structure
(1998,
6,
1095-1103)
copyright 1998.
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