MeuTXKβ1, a scorpion venom-derived two-domain potassium channel toxin-like peptide with cytolytic activity

Recent studies have demonstrated that scorpion venom contains unique two-domain peptides with the peculiarity of possessing different functions, i.e. neurotoxic and cytolytic activities. Here we report systematic characterization of a new two-domain peptide (named MeuTXKβ1) belonging to the TsTXKβ molecular subfamily from the scorpion Mesobuthus eupeus by molecular cloning, biochemical purification, recombinant expression, functional assays, CD and NMR studies. Its full-length bioactive form as well as 1–21 and 22–72 fragments (named N(1–21) and C(22–72), respectively) was produced in Escherichia coli by an on-column refolding approach. Recombinant peptide (rMeuTXKβ1) exhibited a low affinity for K+ channels and cytolytic effects against bacteria and several eukaryotic cells. N(1–21) was found to preserve anti-Plasmodium activity in contrast to haemolytic activity, whereas C(22–72) retains these two activities. Circular dichroism analysis demonstrates that rMeuTXKβ1 presents a typical scorpion toxin scaffold in water and its α-helical content largely increases in a membrane-mimicking environment, consistent with the NMR structure of N(1–21) and an ab initio structure model of MeuTXKβ1 predicted using I-TASSER algorithm. Our structural and functional data clearly indicate an evolutionary link between TsTXKβ-related peptides and antiparasitic scorpines which both comprise the βSPN (β-KTxs and scorpines) family.