Cloning and characterization of cDNA sequences encoding two novel alpha-like-toxin precursors from the Chinese scorpion Buthus martensii Karsch.

According to a relative conserved fragment of alpha-scorpion toxins, a degenerate primer was designed and synthesized. Two full-length cDNAs encoding the precursors of two novel putative alpha-like-toxins were then amplified from the total cDNAs of venomous glands of the Chinese scorpion Buthusmartensi Karsch using 3' and 5' RACE (rapid amplification of cDNA ends). The precursors were both composed of 85 amino acid residues, including a putative signal peptide of 19 residues and a mature toxin of 66 residues, respectively. The predicted amino acid sequences of these two toxins show a homology of 82% with each other, and of 55-70% with other BmK-originated alpha-like-toxins. Interestingly, it is rarely seen in other alpha or alpha-like-toxins that: (1) Met residue but not a basic amino acid residue (Arg or Lys) is located on position 58 for BmKalpha2; (2) both toxins are ended with double Gly in the C-terminus.