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 310-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 240 bp. the deduced precursor open-reading frame was composed of 80 amino acid residues contain a signal peptide of 22 amino acid residues, followed by a mature toxin of 58 amino acids. it had a molecular mass of 6.84 kda and isoelectric point of 4.58. the sequence similarity search revealed several matches with the scorpion toxin-like domain of toxin-3 superfamily with a homology range of 35- 75%. 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.