1bcg
SCORPION TOXIN BJXTR-IT
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OverviewOverview
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 StructureAbout this Structure
1BCG is a Single protein structure of sequence from Hottentotta judaicus. Full crystallographic information is available from OCA.
ReferenceReference
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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