Scorpion depressant β-toxins show high preference for insect voltage-gated sodium channels (Navs) and modulate their activation. Although their pharmacological and physiological effects were described, their three-dimensional structure and bioactive surface have never been determined. We utilized an efficient system for expression of the depressant toxin LqhIT2 (from Leiurus quinquestriatus hebraeus), mutagenized its entire exterior, and determined its X-ray structure at 1.2 Å resolution. The toxin molecule is composed of a conserved cysteine-stabilized α/β-core (core-globule), and perpendicular to it an entity constituted from the N and C-terminal regions (NC-globule). The surface topology and overall hydrophobicity of the groove between the core and NC-globules (N-groove) is important for toxin activity and plays a role in selectivity to insect Navs. The N-groove is flanked by Glu24 and Tyr28, which belong to the "pharmacophore" of scorpion β-toxins, and by the side-chains of Trp53 and Asn58 that are important for receptor site recognition. Substitution of Ala13 by Trp in the N-groove uncoupled activity from binding, suggesting that this region of the molecule is also involved in "voltage-sensor trapping", the mode of action that typifies scorpion β-toxins. The involvement of the N-groove in recognition of the receptor site, which seems to require a defined topology, as well as in sensor trapping, which involves interaction with a moving channel region, is puzzling. On the basis of the mutagenesis studies we hypothesize that following binding to the receptor site, the toxin undergoes a conformational change at the N-groove region that facilitates the trapping of the voltage-sensor in its activated position.
|Number of pages||16|
|Journal||Journal of Molecular Biology|
|State||Published - 16 Feb 2007|
Bibliographical noteFunding Information:
We acknowledge the ESRF in Grenoble for synchrotron beam time and staff scientists of the ID14 station cluster for their assistance. This research was supported by the United States–Israel Binational Agricultural Research and Development grant IS-3480-03 (to M.G. and D.G.); by the Israeli Science Foundation, grants 733/01 (to M.G.) and 1008/05 (to D.G.); and by a grant from the G.I.F., the German-Israeli Foundation for Scientific Research and Development no. G-770-242.1/2002 (to D.G.).
- X-ray structure
- anti-insect selectivity
- bioactive surface
- scorpion depressant toxin
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology