Positions under Positive Selection--Key for Selectivity and Potency of Scorpion  -Toxins

Abstract

Alpha-neurotoxins target voltage-gated sodium channels (Na(v)s) and constitute an important component in the venom of Buthidae scorpions. These toxins are short polypeptides highly conserved in sequence and three-dimensional structure, and yet they differ greatly in activity and preference for insect and various mammalian Na(v)s. Despite extensive studies of the structure-function relationship of these toxins, only little is known about their evolution and phylogeny. Using a broad data set based on published sequences and rigorous cloning, we reconstructed a reliable phylogenetic tree of scorpion alpha-toxins and estimated the evolutionary forces involved in the diversification of their genes using maximum likelihood-based methods. Although the toxins are largely conserved, four positions were found to evolve under positive selection, of which two (10 and 18; numbered according to LqhalphaIT and Lqh2 from the Israeli yellow scorpion Leiurus quinquestriatus hebraeus) have been previously shown to affect toxin activity. The putative role of the other two positions (39 and 41) was analyzed by mutagenesis of Lqh2 and LqhalphaIT. Whereas substitution P41K in Lqh2 did not alter its activity, substitution K41P in LqhalphaIT significantly decreased the activity at insect and mammalian Na(v)s. Surprisingly, not only that substitution A39L in both toxins increased their activity by 10-fold but also LqhalphaIT(A39L) was active at the mammalian brain channel rNa(v)1.2a, which otherwise is hardly affected by LqhalphaIT, and Lqh2(A39L) was active at the insect channel, DmNa(v)1, which is almost insensitive to Lqh2. Thus, position 39 is involved not only in activity but also in toxin selectivity. Overall, this study describes evolutionary forces involved in the diversification of scorpion alpha-toxins, highlights the key role of positions under positive selection for selectivity and potency, and raises new questions as to the toxin-channel face of interaction.

Modular Organization of α-Toxins from Scorpion Venom Mirrors Domain Structure of Their Targets, Sodium Channels

“…4A). The SM seems to evolve more quickly to adjust the toxin specificity to target different Na v s. Note that many of the amino acid residues that have been proposed to evolve under positive selection (66,67) (see red arrows in Fig. 1) are located inside the SM.…”

“…4A). Residues that have been hypothesized to evolve under positive selection are marked with red arrows above (66,67). Fig.…”

Unique diversity of the venom peptides from the scorpion Androctonus bicolor revealed by transcriptomic and proteomic analysis

“…The LD 50 value of the A. bicolor venom in mice was 0.31 mg/kg as tested using intravenous injection [41]. Until now, only two toxic peptides have been identified from the scorpion [42]. To better understand the diversity of the venom peptides from the scorpion, and lay foundation for their applications in both basic research and clinic therapeutics, we employed transcriptomic approaches combined with mass spectrometry to dissect the venom compositions of A. bicolor.…”

“…Using LC-MS/MS, we identified 16 venom peptides from the venom of A. bicolor, of which 15 matched with the peptides deduced from transcripts and 1 matched with a known Na + -channel toxin, Ab8 [42] ( Table 1, Fig. S1 and Fig.…”

“…Scorpionism caused by the scorpion venom is known to lead to human death. However, little has been known about the venom components from A. bicolor so far [15,41,42]. Here, we employed transcriptomic and proteomic approaches to fully explore the diversity of the venom peptides from the scorpion.…”