Characterization of cDNA sequence encoding for a novel sodium channel -toxin from the Iranian scorpion Mesobuthus eupeus venom glands

The venoms of Buthidae scorpions are known to contain basic, single-chain protein -toxins consisting of 60-70 amino acid residues that are tightly cross-linked by four disulfide bridges. Total RNA was extracted from the venom glands of scorpion Mesobuthus eupeus collected from the Khuzestan province of Iran and then cDNA was synthesized with the modified oligo (dT) primer and extracted total RNA as template. By applying the Semi-nested RT-PCR using homologous primers, the fragments of 273 bp was amplified and sequenced. The coding region encodes a polypeptide of 85 amino acid residues with a calculated molecular weight of 9.337 kDa and theoretical isoelectric point of 6.52. It was designated as MeNaTx-4. This peptide with homology to the "Scorpion long chain toxin-like domain" is belongs to the Toxin-3 superfamily. Multiple alignment of the putative amino acid sequence of MeNaTx-4 exhibited 95% sequence identity with lesser Asian scorpion M. eupeus venom sodium channel -toxin-3 but interestingly displayed only 63% identity with other -toxins from this species. The sequence was also identical to the counterpart sequences from M. martensii (92%) and Buthus occitanus israelis (80%). This high sequence similarity together with completely conserved in the positions of all 8 Cys indicated that MeNaTx-4 is a new member of -toxin from the Iranian M. eupeus which may originate from a common ancestor.