Molecular Characterization of a Threedisulfide Bridges Betalike Neurotoxin from Androctonus crassicauda Scorpion Venom

Scorpion venom is the richest source of peptide toxins with high levels of specific interactions with different ionchannel membrane proteins. The present study involved the amplification and sequencing of a 310bp cDNA fragment encoding a betalike neurotoxin active on sodium ionchannel from the venom glands of scorpion Androctonus crassicauda belonging to the Buthidae family using reverse transcription polymerase chain reaction (RTPCR) technique. The amplified complementary DNA (cDNA) fragment had a coding sequence of 240 bp. The deduced precursor openreading 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 toxinlike domain of toxin3 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 longchain 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 ‘shortchain’ and ‘longchain’ toxins. The analysis showed one major segment within this neurotoxin with maximal hydrophilicity which was predicted to be antigenic by inducing an antibody response.