The First K+-Channel Blocker Described from Tityus fasciolatus Venom: The Purification, Molecular Cloning, and Functional Characterization of α-KTx4.9 (Tf5)

Hundreds of toxins, particularly from scorpions of lesser medical significance, remain unknown, especially those from species endemic to specific ecosystems, such as <i>Tityus fasciolatus</i>. Their discovery could contribute to the development of new drugs for channelopathies and other diseases. Tf5 is a new peptide that has been identified from the venom of <i>Tityus fasciolatus</i>, a scorpion species endemic to the Brazilian Cerrado ecosystem. A full-length cDNA sequence of the Tf5 gene was obtained through a previously constructed transcriptomic library, where an ORF (Open Reading Frame) sequence with a length of 180 was found, including the 37 aa mature KTx domain, which has six Cys residues. Tf5 was purified from the crude venom, resulting in a peptide with a molecular mass of 3983.95 Da. Its K⁺ channel blocker activity was evaluated on Kv1.1, Kv1.2, Kv1.3, and Kv1.4 subtypes. Of these Kv channels, the peptide demonstrated an ability to block Kv1.2 and Kv1.3 with an IC₅₀ of 15.53 nM and 116.41 nM, respectively. Additionally, Tf5 shares a high degree of sequence identity with toxins from the α-KTx4 subfamily, which led to it being classified as α-KTx4.9. This is the first Kv channel blocker described from the <i>T. fasciolatus</i> scorpion.