Volume 272, Number 23, Issue of June 6, 1997 pp. 14810-14816
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

Identification of Structural Elements of a Scorpion -Neurotoxin Important for Receptor Site Recognition

(Received for publication, October 22, 1996, and in revised form, February 26, 1997)

Noam Zilberberg , Oren Froy , Erwann Loret ^§ , Sandrine Cestele ^¶ , Dorit Arad , Dalia Gordon and Michael Gurevitz

From the  Department of Plant Sciences and the  Department of Molecular Microbiology and Biotechnology, Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv 69978, Tel-Aviv, Israel, ^§ IBSM-LIDSM-CNRS-UPR 9027, 31 Chemin Joseph Aiguier, BP 71, 13402, Marseille Cedex 20, France, and the ^¶ Laboratoire de Biochimie, CNRS URA 1455, Faculte de Medicine, Secteur Nord, 13916 Marseille Cedex 20, France

-Neurotoxins from scorpion venoms constitute the most studied group of modifiers of the voltage-sensitive sodium channels, and yet, their toxic site has not been characterized. We used an efficient bacterial expression system for modifying specific amino acid residues of the highly insecticidal -neurotoxin LqhIT from the scorpion Leiurus quinquestriatus hebraeus. Toxin variants modified at tight turns, the C-terminal region, and other structurally related regions were subjected to neuropharmacological and structural analyses. This approach highlighted both aromatic (Tyr¹⁰ and Phe¹⁷) and positively charged (Lys⁸, Arg¹⁸, Lys⁶², and Arg⁶⁴) residues that (i) may interact 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 electrostatic potential that may be involved in biorecognition of the receptor site. The latter was supported by a suppressor mutation (E15A) that restored a detrimental effect caused by a K8D substitution. The feasibility of producing anti-insect scorpion neurotoxins with augmented toxicity was demonstrated by the substitution of the C-terminal arginine with histidine. Altogether, the present study provides for the first time an insight into the putative toxic surface of a scorpion neurotoxin affecting sodium channel gating.

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