A. Jolodar - Department of Basic Sciences, Biochemistry and Molecular Biology Section, Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Ahvaz, Iran

Scorpion venom is the richest source of peptide toxins with high levels of specific interactions with different ion-channel membrane proteins. The present study involved the amplification and sequencing of a ۳۱۰-bp cDNA fragment encoding a beta-like neurotoxin active on sodium ion-channel from the venom glands of scorpion Androctonus crassicauda belonging to the Buthidae family using reverse transcription polymerase chain reaction (RT-PCR) technique. The amplified complementary DNA (cDNA) fragment had a coding sequence of ۲۴۰ bp. The deduced precursor open-reading frame was composed of ۸۰ amino acid residues contain a signal peptide of ۲۲ amino acid residues, followed by a mature toxin of ۵۸ amino acids. It had a molecular mass of ۶.۸۴ kDa and isoelectric point of ۴.۵۸. The sequence similarity search revealed several matches with the scorpion toxin-like domain of toxin-۳ superfamily with a homology range of ۳۵- ۷۵%. Multiple alignments and secondary structure prediction demonstrated that the toxin peptide deduced from the amplified cDNA was related to the long-chain neurotoxins in size but stabilized by three disulfide bridges instead of four. The level of difference implies that the corresponding genes have originated from a common ancestor. This level of difference may also confirm an evolutionary link between the ‘short-chain’ and ‘long-chain’ toxins. The analysis showed one major segment within this neurotoxin with maximal hydrophilicity which was predicted to be antigenic by inducing an antibody response.

Androctonus crassicauda, Beta-neurotoxin, Disulfide bridges