Isolation and characterization of Ts19 Fragment II, a new long-chainpotassium channel toxin from Tityus serrulatus venom

Ts19 Fragment II (Ts19 Frag-II) was first isolated from the venom of the scorpion Tityus serrulatus (Ts). It is aprotein presenting 49 amino acid residues, three disulfide bridges, Mr5534 Da and was classified as a newmember of class (subfamily) 2 of the -KTxs, the second one described for Ts scorpion. The -KTx familyis composed by two-domain peptides: N-terminal helical domain (NHD), with cytolytic activity, and aC-terminal CS domain (CCD), with Kv blocking activity. The extensive electrophysiological screening(16 Kv channels and 5 Nav channels) showed that Ts19 Frag-II presents a specific and significant blockingeffect on Kv1.2 (IC50value of 544 ± 32 nM). However, no cytolytic activity was observed with this toxin.We conclude that the absence of 9 amino acid residues from the N-terminal sequence (compared to Ts19Frag-I) is responsible for the absence of cytolytic activity. In order to prove this hypothesis, we synthesizedthe peptide with these 9 amino acid residues, called Ts19 Frag-III. As expected, Ts19 Frag-III showed tobe cytolytic and did not block the Kv1.2 channel. The post-translational modifications of Ts19 and itsfragments (I–III) are also discussed here. A mechanism of post-translational processing (post-splitting) issuggested to explain Ts19 fragments production. In addition to the discovery of this new toxin, this reportprovides further evidence for the existence of several compounds in the scorpion venom contributing tothe diversity of the venom arsenal.