1bcg
From Proteopedia
(New page: 200px<br /><applet load="1bcg" size="450" color="white" frame="true" align="right" spinBox="true" caption="1bcg, resolution 2.10Å" /> '''SCORPION TOXIN BJXTR...) |
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| - | [[Image:1bcg.gif|left|200px]]<br /><applet load="1bcg" size=" | + | [[Image:1bcg.gif|left|200px]]<br /><applet load="1bcg" size="350" color="white" frame="true" align="right" spinBox="true" |
caption="1bcg, resolution 2.10Å" /> | caption="1bcg, resolution 2.10Å" /> | ||
'''SCORPION TOXIN BJXTR-IT'''<br /> | '''SCORPION TOXIN BJXTR-IT'''<br /> | ||
==Overview== | ==Overview== | ||
| - | BACKGROUND: Scorpion neurotoxins, which bind and modulate sodium channels, have been divided into two groups, the alpha and beta toxins, according to | + | 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. |
==About this Structure== | ==About this Structure== | ||
| - | 1BCG is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Hottentotta_judaicus Hottentotta judaicus]. Full crystallographic information is available from [http:// | + | 1BCG is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Hottentotta_judaicus Hottentotta judaicus]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1BCG OCA]. |
==Reference== | ==Reference== | ||
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[[Category: excitatory neurotoxin]] | [[Category: excitatory neurotoxin]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 11:53:53 2008'' |
Revision as of 09:53, 21 February 2008
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SCORPION TOXIN BJXTR-IT
Overview
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.
About this Structure
1BCG is a Single protein structure of sequence from Hottentotta judaicus. Full crystallographic information is available from OCA.
Reference
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., Oren DA, Froy O, Amit E, Kleinberger-Doron N, Gurevitz M, Shaanan B, Structure. 1998 Sep 15;6(9):1095-103. PMID:9753689
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