-Scorpion Toxins Binding on Rat Brain and Insect Sodium Channels Reveal Divergent Allosteric Modulations by Brevetoxin and Veratridine

doi:10.1074/jbc.270.25.15153

-Scorpion Toxins Binding on Rat Brain and Insect Sodium Channels Reveal Divergent Allosteric Modulations by Brevetoxin and Veratridine (*)

From the (1) Faculty of Medicine Nord, Institut Féderatif de Recherche Jean Roche, Laboratory of Biochemistry, URA CNRS 1455, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France and the
(2)Laboratory of Neurophysiology, URA CNRS 611, University of Angers, 49045 Angers Cedex, France

^¶ To whom correspondence should be addressed. Tel.: 33-91-96-20-67; Fax: 33-91-65-75-95; E-mail: gordon{at}citi2.fr.

Abstract

At least six topologically separated neurotoxin receptor sites have been identified on sodium channels that reveal strong allosteric interactions among them. We have studied the allosteric modulation induced by veratridine, binding to receptor site 2, and brevetoxin PbTx-1, occupying receptor site 5, on the binding of α-scorpion toxins at receptor site 3, on three different neuronal sodium channels: rat brain, locust, and cockroach synaptosomes. We used I-AaH II, the most active α-scorpion toxin on vertebrates, and I-LqhαIT, shown to have high activity on insects, as specific probes for receptor site 3 in rat brain and insect sodium channels. Our results reveal that brevetoxin PbTx-1 generates three types of effects at receptor site 3: 1) negative allosteric modulation in rat brain sodium channels, 2) positive modulation in locust sodium channels, and 3) no effect on cockroach sodium channel. However, PbTx-1 activates sodium channels in cockroach axon similarly to its activity in other preparation. Veratridine positively modulates both rat brain and locust sodium channels but had no effect on α-toxin binding in cockroach. The dramatic differences in allosteric modulations in each sodium channel subtype suggest structural differences in receptor sites for PbTx-1 and/or at the coupling regions with α-scorpion toxin receptor sites in the different sodium channels, which can be detected by combined application of specific channel modifiers and may elucidate the dynamic gating activity and the mechanism of allosteric interactions among various neurotoxin receptors.

Footnotes

↵^§ A recipient of a fellowship from the “Ministere de la recherche et de la technologie.”
↵* This work was supported by a research grant from the Franco-Israeli Association for Scientific and Technologic Research (AFIRST) (to H. R.) and from U.S.A.-Israel Binational Science Foundation Grant 93-00294 (to D. G.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

BTX

batrachotoxin

AaH II

α-toxin II from the venom of the scorpion A. australis Hector

[³H]BTX-B

[³H]batrachotoxin A 20-α-benzoate

CNS

central nervous system

LqhαIT

α-toxin specific to insects, from the venom of the scorpion Leiurus quinquestriatus hebreus

LqhIT²

depressant insect-selective toxin from the scorpion L. quinquestriatus hebreus

Lqq V

α-toxin V from the venom of the scorpion Leiurus quinquestriatus quinquestriatus, also called LqTx or ScTx

PbTx

brevetoxin from the marine dinoflagellate Ptychodiscus brevis.
↵²D. Gordon and S. Cestèle, unpublished results.
↵³Y. Pichon, personal communication.