Molecular requirements for recognition of brain voltage-gated sodium channels by scorpion α-toxins

The scorpion α-toxin Lqh2 (firqm Leiurus quinquestriatus hebraeus) is active at various mammalian voltage-gated sodium channels (Na_vs) and is inactive it insect Na_vs. To resolve the molecular basis of this preference we used the following strategy: 1) Lqh2 was expressed in recombinant form and key residues important for activity at the rat brain channel rNa_v1.2a were identified by mutagenesis. These residues form a bipartite functional surface made of a conserved "core domain" (residues of the loops connecting the secondary structure elements of the molecule core), and a variable "NC domain" (five-residue turn and the C-tail) as was reported for other scorpion α-toxins. 2) The functional role of the two domains was validated by their stepwise construction on the similar scaffold of the anti-insect toxin LqhαIT. Analysis of the activity of the intermediate constructs highlighted the critical role of Phe¹⁵ of the core domain in toxin potency at rNa_v1.2a, and has suggested that the shape of the NC-domain is important for toxin efficacy. 3) Based on these findings and by comparison with other scorpion α-toxins we were able to eliminate the activity of Lqh2 at rNa_v1.4 (skeletal muscle), hNa_v1.5 (cardiac), and rNa_v1.6 channels, with no hindrance of its activity at Na_v.1.1-1.3. These results suggest that by employing a similar approach the design of further target-selective sodium channel modifiers is imminent.