IDENTIFICATION OF STRUCTURAL ELEMENTS OF A SCORPION ALPHA-NEUROTOXIN IMPORTANT FOR RECEPTOR-SITE RECOGNITION

alpha-Neurotoxins from scorpion venoms constitute the most studied gro up of modifiers of the voltage-sensitive sodium channels, and yet, the ir toxic site has not been characterized. We used an efficient bacteri al expression system for modifying specific amino acid residues of the highly insecticidal alpha-neurotoxin Lqh alpha IT from the scorpion L eiurus quinquestriatus hebraeus. Toxin variants modified at tight turn s, the C-terminal region, and other structurally related regions were subjected to neuropharmacological and structural analyses. This approa ch highlighted both aromatic (Tyr(10) and Phe(17)) and positively char ged (Lys(8), Arg(18), Lys(62), and Arg(64)) residues that (i) may inte ract directly with putative recognition points at the receptor site on the sodium channel; (ii) are important for the spatial arrangement of the toxin polypeptide; and (iii) contribute to the formation of an el ectrostatic potential that may be involved in biorecognition of the re ceptor site. The latter was supported by a suppressor mutation (E15A) that restored a detrimental effect caused by a K8D substitution. The f easibility of producing anti-insect scorpion neurotoxins with augmente d toxicity was demonstrated by the substitution of the C-terminal argi nine with histidine. Altogether, the present study provides for the fi rst time an insight into the putative toxic surface of a scorpion neur otoxin affecting sodium channel gating.