The differential preference of scorpion α-toxins for insect or mammalian sodium channels: Implications for improved insect control (original) (raw)
Related papers
Biochemistry, 1992
Site-directed antibodies corresponding to conserved putative extracellular segments of sodium channels, coupled with binding studies of radiolabeled insect-selective scorpion neurotoxins, were employed to clarify the relationship between the toxins' receptor sites and the insect sodium channel. (1) The depressant insect toxin LqhIT2 was shown to possess two noninteracting binding sites in locust neuronal membranes: a high-affinity (KD, = 0.9 f 0.6 nM) and low-capacity (Bmax, = 0.1 f 0.07 pmol/mg) binding site as well as a low-affinity (KD, = 185 f 13 nM) and high-capacity (Bmaxz = 10.0 f 0.6 pmol/mg) binding site. The high-affinity site serves as a target for binding competition by the excitatory insect toxin AaIT. The binding of LqhIT2 was significantly inhibited in a dose-dependent manner by each of four site-directed antibodies. The binding inhibition resulted from reduction in the number of binding sites. (4) The antibodymediated inhibition of [1251]AaIT binding differs from that of LqhIT2: three out of the four antibodies which inhibited LqhIT2 binding only partially affected AaIT binding. Two antibodies, one corresponding to extracellular and one to intracellular segments of the channel, did not affect the binding of either toxin. These data suggest that the receptors to the depressant and excitatory insect toxins (a) comprise an integral part of the insect sodium channel, (b) are formed by segments of external loops in domains I, 111, and IV of the sodium channel, and (c) are localized in close proximity but are not identical in spite of the competitive interaction between these toxins.
FEBS Letters, 2003
Intensive pyrethroid use in insect control has led to resistance buildup among various pests. One alternative to battle this problem envisions the combined use of synergistically acting insecticidal compounds. Pyrethroids, scorpion K K-and L L-toxins, and brevetoxins bind to distinct receptor sites on voltage-gated sodium channels (NaChs) and modify their function. The binding a⁄nity of scorpion K K-toxins to locust, but not ratbrain NaChs, is allosterically increased by pyrethroids and by brevetoxin-1. Brevetoxin-1 also increases the binding of an excitatory L L-toxin to insect NaChs. These results reveal di¡erences between insect and mammalian NaChs and may be exploited in new strategies of insect control. ß
Biochemistry, 2005
δ-Palutoxins from the spider Paracoelotes luctuosus (Araneae: Amaurobiidae) are 36-37 residue long peptides that show preference for insect sodium channels (NaChs) and modulate their function. Although they slow NaCh inactivation in a fashion similar to that of receptor site 3 modifiers, such as scorpion R-toxins, they actually bind with high affinity to the topologically distinct receptor site 4 of scorpion -toxins. To resolve this riddle, we scanned by Ala mutagenesis the surface of δ-PaluIT2, a δ-palutoxin variant with the highest affinity for insect NaChs, and compared it to the bioactive surface of a scorpion -toxin. We found three regions on the surface of δ-PaluIT2 important for activity: the first consists of Tyr-22 and Tyr-30 (aromatic), Ser-24 and Met-28 (polar), and Arg-8, Arg-26, Arg-32, and Arg-34 (basic) residues; the second is made of Trp-12; and the third is made of Asp-19, whose substitution by Ala uncoupled the binding from toxicity to lepidopteran larvae. Although spider δ-palutoxins and scorpion -toxins have developed from different ancestors, they show some commonality in their bioactive surfaces, which may explain their ability to compete for an identical receptor (site 4) on voltage-gated NaChs. Yet, their different mode of channel modulation provides a novel perspective about the structural relatedness of receptor sites 3 and 4, which until now have been considered topologically distinct.
European Journal of Neuroscience, 1999
α-Like toxins, a unique group designated among the scorpion α-toxin class that inhibit sodium channel inactivation, are highly toxic to mice but do not compete for α-toxin binding to receptor site 3 on rat brain sodium channels. We analysed the sequence of a new α-like toxin, which was also highly active on insects, and studied its action and binding on both mammalian and insect sodium channels. Action of the α-like toxin on isolated cockroach axon is similar to that of an α-toxin, and the radioactive toxin binds with a high affinity to insect sodium channels. Other sodium channel neurotoxins interact competitively or allosterically with the insect α-like toxin receptor site, similarly to α-toxins, suggesting that the α-like toxin receptor site is closely related to receptor site 3.
Variability among insect sodium channels revealed by selective neurotoxins
Insect Biochemistry and Molecular Biology, 1994
Binding assays with the radioiodinated depressant (LqhlTz) and excitatory (AalT) insect selective neurotoxins derived from scorpion venoms to neuronal membrane preparations derived from cockroach, fly and lepidopterous larvae coupled with the employment of sodium channel site-directed antibodies resulted in the following information. (1) The two toxins were shown to bind with high affinity to the insect neuronal preparations and revealed similar binding constants in each of the various preparations.
Invertebrate Neuroscience, 1997
Voltage-sensitive sodium channels are responsible for the generation of electrical signals in most excitable tissues and serve as specific targets for many neurotoxins. At least seven distinct classes of neurotoxins have been designated on the basis of physiological activity and competitive binding studies. Although the characterization of the neurotoxin receptor sites was predominantly performed using vertebrate excitable preparations, insect neuronal membranes were shown to possess similar receptor sites. We have demonstrated that the two mutually competing antiinsect excitatory and depressant scorpion toxins, previously suggested to occupy the same receptor site, bind to two distinct receptors on insect sodium channels. The latter provides a new approach to their combined use in insect control strategy. Although the sodium channel receptor sites are topologically separated, there are strong allosteric interactions among them. We have shown that the lipid-soluble sodium channel activators, veratridine and brevetoxin, reveal divergent allosteric modulation on scorpion a-toxins binding at homologous receptor sites on mammalian and insect sodium channels. The differences suggest a functionally important structural distinction between these channel subtypes. The differential allosteric modulation may provide a new approach to increase selective activity of pesticides on target organisms by simultaneous application of allosterically interacting drugs, designed on the basis of the selective toxins. Thus, a comparative study of neurotoxin receptor sites on mammalian and invertebrate sodium channels may elucidate the structural features involved in the binding and activity of the various neurotoxins, and may offer new targets and approaches to the development of highly selective pesticides.
Journal of Biological Chemistry, 1996
Sodium channels posses receptor sites for many neurotoxins, of which several groups were shown to inhibit sodium current inactivation. Receptor sites that bind ␣and ␣-like scorpion toxins are of particular interest since neurotoxin binding at these extracellular regions can affect the inactivation process at intramembranal segments of the channel. We examined, for the first time, the interaction of different scorpion neurotoxins, all affecting sodium current inactivation and toxic to mammals, with ␣-scorpion toxin receptor sites on both mammalian and insect sodium channels. As specific probes for rat and insect sodium channels, we used the radiolabeled ␣-scorpion toxins AaH II and Lqh␣IT, the most active ␣-toxins on mammals and insect, respectively. We demonstrate that the different scorpion toxins may be classified to several groups, according to their in vivo and in vitro activity on mammalian and insect sodium channels. Analysis of competitive binding interaction reveal that each group may occupy a distinct receptor site on sodium channels. The ␣-mammal scorpion toxins and the anti-insect Lqh␣IT bind to homologous but not identical receptor sites on both rat brain and insect sodium channels. Sea anemone toxin ATX II, previously considered to share receptor site 3 with ␣-scorpion toxins, is suggested to bind to a partially overlapping receptor site with both AaH II and Lqh␣IT. Competitive binding interactions with other scorpion toxins suggest the presence of a putative additional receptor site on sodium channels, which may bind a unique group of these scorpion toxins (Bom III and IV), active on both mammals and insects. We suggest the presence of a cluster of receptor sites for scorpion toxins that inhibit sodium current inactivation, which is very similar on insect and rat brain sodium channels, in spite of the structural and pharmacological differences between them. The sea anemone toxin ATX II is also suggested to bind within this cluster.
Binding of an α scorpion toxin to insect sodium channels is not dependent on membrane potential
FEBS Letters, 1993
The insect-specific LqhaIT toxin resembles a scorpion toxins affecting mammals by its amino acid sequence and effects on sodium conductance. The present study reveals that LqhaIT does not bind to rat brain membranes and possesses in locust neuronal membranes a single class of high affinity (& = 1.06 f 0.15 nM) and low capacity (B,,,, = 0.7 f 0.19 pmol/mg protein) binding sites. The latter are: (1) distinct from binding sites of other sodium channel neurotoxins; (2) inhibited by sea anemone toxin II; (3) cooperatively interacting with veratridine; (4) not dependent on membrane potential, in contrast to the binding sites of a toxins in vertebrate systems. These data suggest the occurrence of (a) conformationalstructural differences between insect and mammal sodium channels and (b) the animal group specificity and pharmacological importance of the u scorpion toxins.