Molecular Characterization of a Three-disulfide Bridges Beta-like Neurotoxin from Androctonus crassicauda Scorpion Venom

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.

Keywords:

Androctonus crassicauda , Beta-neurotoxin , Disulfide bridges