Molecular Requirements for Recognition of Brain Voltage-gated Sodium Channels by Scorpion α-Toxins

Abstract

The scorpion ␣-toxin Lqh2 (from Leiurus quinquestriatus hebraeus) is active at various mammalian voltage-gated sodium channels (Na v s) and is inactive at insect Na v s. 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 v 1.2a 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 ␣-toxins.2) The functional role of the two domains was validated by their stepwise construction on the similar scaffold of the anti-insect toxin Lqh␣IT. Analysis of the activity of the intermediate constructs highlighted the critical role of Phe 15 of the core domain in toxin potency at rNa v 1.2a, 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 ␣-toxins we were able to eliminate the activity of Lqh2 at rNa v 1.4 (skeletal muscle), hNa v 1.5 (cardiac), and rNa v 1.6 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.

Common Molecular Determinants of Tarantula Huwentoxin-IV Inhibition of Na+ Channel Voltage Sensors in Domains II and IV

“…Scorpion ␤-toxins bind to the DII voltage sensor to enhance voltage-dependent activation by trapping DIIS4 in the activated state (10 -12). Scorpion ␣-toxins bind to the DIV voltage sensor and inhibit fast inactivation by trapping DIVS4 in the closed state (13,14). These findings seem to suggest that there are substantial differences between the toxin-binding sites on the voltage sensors of DII and DIV.…”

Mapping the receptor site for α-scorpion toxins on a Na + channel voltage sensor

“…LqhII was produced as described (24,40). Structural modeling was carried out as described (30,31,(41)(42)(43).…”

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

“…4A). Although previous studies suggested the division of ␣-toxin molecules into two parts (37,39,41,62), never before was this clearly illustrated from the MD and surface hydrophobicity. 3) Functionally, the core module seems to determine the overall ability of ␣-toxins to target Na v s, whereas the SM determines toxin specificity and eventually its classification as mammal, insect, or ␣-like.…”